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Calathea rufibarba, a beautiful yet rarely grown species with fuzzy, scalloped leaves which are a deep green above and purple below. Certainly a little more interesting than a Spathiphyllum or other similarly-sized plant, this species garners a good amount of attention. Image © In Situ Plants.

Anthurium superbum, a species with beautiful bullate leaves that thrives in bright indirect light. Image © In Situ Plants.

There are an estimated 400,000 species of plants on earth. While this includes species such as giant marine kelp, leafless parasitic plants, and a slough of other ones not ultimately suitable for indoor cultivation, there are a significant number which will do quite well in an interior setting provided a few basic conditions are met, and certainly more species than are typically seen indoors.

It seems then a disservice to our clients, our own industry and plants in general that most companies seem to prefer to play it safe with the tried-and-true varieties that we’ve all become so accustomed to seeing. They’re about as common as dirt, as the saying goes, and, besides the fact that they (hopefully) have been grown as premium interior specimens and not hastened out the greenhouse door in the fashion of so many of the houseplants sold to the consumer market (the subject of another forthcoming post, I’m sure), there’s not really much to differentiate them from the plants that people are growing on their own at home, or at least that they’re so used to seeing everywhere that they don’t even notice them anymore.

It’s a disservice to clients because, while presumably done with good intentions in order to spare clients the sight of an ailing plant should anything go awry (most of these are very tough to kill [or at least they die slowly and relatively gracefully], and perform fairly predictably), it doesn’t really deliver a tremendous amount of value to the client: certainly they will get the physical benefits of having plants indoors (these benefits were touched on in this post), but the aesthetic and biophilic benefits of plants seem to me somewhat dependent on the plants being engaging and actually noticed, instead of looking like furniture as they so often do. And why have something commonplace when something extraordinary is just as much cost (on their part) and effort (on our part)?

It’s a disservice to our industry for several reasons. As I noted above, to the untrained eye these species, even if they’ve been better grown, look nearly indistinguishable from the ones that can be bought for a pittance at a big box store or wherever; it is challenging to justify the price point for them when someone thinks that they’re the same as the ones they saw for a quarter of the price up the road, even if they get the whole spiel about quality, etc. The other side to this is that many people grow these plants in their home themselves; why, then, would they pay us to do it? Yes, we can do a much better job (hopefully!), but it’s just another aspect we need to justify to the customer. Granted, there are some situations (extreme low light, for example) where only the bulletproof plants will do, but in most situations there is likely something more unique that could be used.

Lastly, it’s a disservice to plants (not that they care): what better way to share a passion for all things green than to try and show the public as much of that world as we can? There’s just so much out there that it seems strange to restrict ourselves to the commonplace when we’re in the business of bringing life into our clients’ spaces; certainly showcasing the extraordinary biodiversity that the plant kingdom has to offer is an effective way of doing just this.

Plants are able to do so much for us, and technology now makes it easier to keep species with particular requirements happy without any additional work (the Calathea above would certainly be trickier without the sub-irrigated planters it’s in; it’s relatively easy to grow so long as it doesn’t go dry). Vertical gardens allow the perfect growing environment for plants so uncommon in cultivation that they don’t even have a common name; the combination of ample water and high humidity makes a huge variety of plants available to the vertical gardener. What a shame then to see so many large, high-profile projects populated by pothos and other common plants when the whole of the tropics could have been the designer’s oyster.

In Situ challenges all in our industry (growers, local wholesalers and interior landscaping firms) to venture off the well-trodden path of Dracaena and Schefflera and step into a world rich in plant species which can grow our industry and the public’s love and appreciation for plants indoors.

Feeding damage caused by thrips to a pothos leaf before it has fully developed, resulting in distortion and necrotic patches. Regrettably out of focus image © Plantscape Designs, Inc.; image retrieved from their blog.

Amblyseius cucumeris, a mite predator of thrips, in a moment of glory. Image © Rosemarije Buitenhuis; image retrieved from an article on thrips on the Greenhouse Canada website.

Feeding damage and feces left behind by thrips, the rude little buggers. Image © the respective photographer (there are several credited on the page); retrieved from the University of California, Riverside

When one reads about pests in the interior landscape, spider mites, scale and mealybug are the most often mentioned, and with good reason: these creatures can, if conditions are right, completely overwhelm a plant, literally sucking the life from it. Even if they don’t, they can cause plants to be unsightly, and, in the case of the latter two insects, can cover the plant and the immediate area with sticky honeydew which is a bitch to clean. The signs of their presence are usually fairly obvious: spider mites create webs which can cover leaf surfaces and their feeding damage gives foliage a speckled appearance; scale will populate the foliage and stems with their dark, bumpy selves, and mealybug will crowd leaf axils and stems with their cottony badness.

And then there are thrips; they are small enough that most of the time you won’t know they’re there, and the damage they inflict on plants is often confusing and can lead one to believe that something else is responsible. And often when I’m assessing a problematic plant and mention them, people will frown and ask, ‘What are thrips?’ Hence this post.

Thrips is a large family of insects, many species of which are serious agricultural pests. (And yes, the singular and plural pronunciation and spelling is the same.) Because they have the ability to reproduce so rapidly, they can quickly develop resistance to chemical insecticides, making them a serious nuisance.

Because they feed primarily on new growth (including leaves, flowers and fruit), the damage they do is often caused before this new growth develops fully: flowers and leaves then open with distorted shapes, necrotic patches and streaks that can resemble disease, mechanical damage or nutrient deficiency. They can also feed on matured foliage, leaving behind silverish patches which in some species can become bronze-coloured or corky with time. They are, as I mentioned above, quite tiny, and when hidden deep in a flower bud or the like can be practically invisible. Knocking the plant part while holding it above a white sheet of paper will often dislodge a few and reveal their presence, and they do leave dark little globs of feces near feeding damage as well.

t is not merely enough for them to be sneaky, tiny, and voracious; they are also incredibly mobile. I have visited sites where every single plant on an entire office floor was afflicted (granted, it was stocked mostly with thrips’ favourite food, but still). They are capable of flight and also of being carried by the breeze due to their tiny size (not that this is as much a problem indoors). They also breed at a pace that would make a rabbit blush; they can complete the cycle from egg to breeding adult in as little as two weeks if temperatures are high enough to permit it.

This latter fact is one of the main challenges with their management by chemical means; as they reproduce so quickly, they are able to just as quickly develop resistance to insecticides, and thus these only offer a measure of control for a short time before they are useless. Irresponsible use of these chemicals by producers (failing to rotate chemicals, calendar spraying, and incorrect technique) have not helped the situation, and in fact, probably the most widespread of these beasts in Canadian ornamental horticulture, the western flower thrips, is now resistant to most chemical insecticides.

But before your despair causes you to throw your scarred old pothos into the compost, wait: there is hope in the form of biological control. There are many predators of thrips in nature, and several are able to be commercially raised for use in controlling them. Natural Insect Control, Inc. of Stevensville, Ontario is our most local option here in Toronto, and offers several of these in varying increments, the most common and economical being Amblyseius cucumeris, a predatory mite with a healthy appetite for thrips. This is a great solution if you’re not anti-bug in general (you’ll be intentionally releasing thousands of mites into your plants, after all), though to their further credit they are also very small and innocuous. I won’t get into the importance of knowing a little bit about the life cycle and natural history of both thrips and these mites in order to have optimal success with this technique; that’s a whole other blog post, at least. Suffice to say that it’s definitely a good option, particularly if you have many afflicted plants or what you’re trying to save is of high value (A. cucumeris are reasonably priced, by biological control standards, but certainly cost more than the average plant that one might buy at a garden centre or the like). There are several other thrips predators available to consumers such as Orius insidiosus and several other mite species, but as mentioned above, A. cucumeris is the most economical.

Another option is using products containing spinosad; these have only recently become available to consumers in Canada, so far as I know. They contain spinosyns, which are compounds which were discovered by fermenting a bacteria found at a rum distillery in the Virgin Islands(!); you can read the dry version of that here. Spinosad is wonderfully effective at controlling thrips, as it happens; I first read about it perhaps six years ago as a good tool against thrips in people’s orchid collections, and it has certainly knocked down populations that I’ve treated. There have been reports of thrips developing resistance to spinosyns, so applying sparingly and rotating with another product and/or in conjunction with a thrips predator so that the spray is used less often would help to minimize this effect.

Some products containing spinosad are approved for organic agriculture, which is enticing, though it should be noted that it is very noxious to bees, and so care should be taken with the product in that regard. The LD50 for this stuff is absurdly high compared to pyrethrin, a derivative of chrysanthemum flowers which is used in over-the-counter insecticides, which effectively means that it’s safer (the LD50 actually means that it takes whatever the number is worth of milligrams of compound per kilogram of an animal’s body weight to kill 50% of a population of said animal; a bit strange, but that’s the standard): according to the LD50, presuming you’re as sensitive to this compound as mice or rats and near median human weight, you would need to ingest 310 grams of it in order for it to be fatal; a feat, to be sure.

There are other non-chemical options available to commercial producers which are effective, and which seem to be trickling down and becoming available to the rest of us: the entomopathogenic fungus Beauvaria bassiana has been used as an ingredient in commercially available products for at least several years, and consumer-packaged products are available for order online from out of the country. There is not yet such a product being sold on shelves in Canada, so far as I know.

If you have these pests, you’ll likely be wanting to do something, as they can overwhelm a plant if they like it enough. The pothos pictured above is a common example of a member of the family Araceae, which all the way across the board has been a magnet for thrips, in my experience: Monstera, Philodendron, Anthurium, Spathiphyllum; all of these have fallen prey to the tiny rasping mouthparts of these miniature beasts, while other plants have grown in close contact without sustaining so much as a nibble. There are other susceptible species amongst common and rare indoor plants, and they love many species grown for cut flowers such as chryanthemums and gerbera daisies, to which they cause huge economic damage every year in production greenhouses; tap your bouquets over a sheet of white paper before you set a vase full near your houseplants!

Because their life cycle is so rapid, treatment will need to be fairly frequent in order to ensure they do get knocked down. Biological controls should be released at regular intervals, as many predators such as A. cucumeris feed only on younger thrips and can’t manage the adults (O. insidiosus certainly can, and it’s a joy to watch under magnification, but these guys don’t come cheap).

So that’s the story about thrips; controlling them can be a challenge, so have a close look at any plant you’re thinking of taking home, because you know what they say about an ounce of prevention…

Anoectochilus formosanus, a beautifully-patterned small species of orchid which grows terrestrially in leaf litter in its native habitat, and which loves the moist humid surroundings of a terrarium. Image © In Situ Plants.

The tropical understory; a wealth of interesting species often better suited to the confines of the humid terrarium than the oft-toted succulents. Image © In Situ Plants.

Mosses, to me, are some of the most lush and beautiful plants one can grow, and they do best in a humid terrarium. Image © In Situ Plants.

Peperomia prostrata, a long-standing terrarium favourite which is also quite cute and succulent-looking. Image © In Situ Plants.

You’ve likely read me hint before about my disdain for the current craze in succulent plants, and succulent terrariums in particular. Don’t get me wrong: I’m glad to see an interest in plants in general, and I have nothing against the plants themselves, really; there are a lot of interesting plants that are classified as succulents, displaying a huge variety of shape, colour, and texture, which I suppose is the appeal.They have a reputation of being hard to kill, which I’ll admit is partially true; they grow easily enough when conditions are favourable, and if they are not, most of them are at least slow to decline if pretty much left alone, though improper care can hasten their end, especially via overwatering. They are inxepensive, though (particularly the cute young plants that florists and the like get in), and so are easy to replace when one knocks off.

But are people satisfied with this? Isn’t the whole thing about keeping plants to try and keep them alive and doing well? I’ll readily admit to having killed a plant or two in my time (not usually for lack of trying), but one of the first things I think about when I find a plant I like the look of is whether it’s suited to my growing conditions, and, for me at least, most succulents are patently not. They require (for the most part) very bright light, which is an immediate turn off for me personally, and should be for most people I meet who profess to be ‘really into succulents right now’, most of whom don’t have a window with decent exposure, let alone the solarium or greenhouse that would really allow these plants to do their thing.

These plants end up being stuck in a seashell, a shot glass, or some other kitschy place, or worse yet, a terrarium, where conditions are not exactly optimal; these plants are adapted to arid regions, and most require very bright light, free-draining soil and good air movement to do well, and without special considerations these can be very difficult to achieve in a terrarium environment, which are by design retentive of moisture and humidity.

Seeing as how one might have a glass vessel around after succulent disasters of one kind or another (if not, they’re readily available from many stores now in various shapes and sizes, though of course any glass or otherwise transparent container will do, really), why not give one a go again with plants that are perfectly at home therein? The really nice ones (such as the orchid to the right) can take a little digging to rustle up, but there are many fine species which can be found without too much trouble and with which one can have some rewarding success with terrarium gardening. Because the terrarium should really be a less intensive and more problem-free way to keep plants indoors; soil moisture is held much longer, so issues with forgetting a watering will not be as severe, and most plants will benefit from the extra humidity and reward the grower with larger, vibrant-looking foliage while at the same time avoiding the many foliar maladies that come with dry indoor air.

This was the original purpose of the terrarium, after all; Wardian cases have been around since the Victorian age as a way of keeping exotic tropical plants alive indoors, which was the style at the time. Ferns and the like were and are appreciative of the shelter provided by these glass enclosures, and we now have better technology which allows us to have seamless (and leadless!) glass enclosures for these plants, which makes them all the more attractive while still being quite functional.

What are the prerequisites for a good terrarium plant? First and foremost the plant needs to be adapted to the conditions approximated by a terrarium, which typically consist of lower light, consistently moist soil, higher humidity, lower air movement and limited space, though all of these variables can be controlled to some degree. Fortunately there are many plants who are right at home in such an environment; think of the tropical forest understory, where the light is dim and the air and soil are often very damp indeed. Many species can be found either growing directly on the ground or else epiphytically on the lower portions of trees, and these are often the best suited for terrarium life.

There are plenty of blogs and articles out there that list suitable species, so I won’t bother with one here. Be wary, though, as some of these lists are not entirely well thought out and some of the listed species may eventually grow quite large (relatively speaking); when starting out, working with a larger container will help keep things manageable without needing too much maintenance to keep things from being cramped. Do a little research and find out the maximum size of any prospective species and it will save you trouble in the long run. There are a great many true miniature plants which will stay small for their entire lives, but they are often not available through most retailers, who instead often sell juvenile plants in small pots because they’re cute and inexpensive. An alternative might be creeping or stoloniferous plants, for example, like Pellionia, Pilea, Episcia and others, which are pretty easy to find; their size is very easily managed, for they stay low to the ground and need only be trimmed when they start climbing the walls of the terrarium. There are many upright plants which will stay reasonably short in stature that pass through the garden centres and florists’ often enough, too, so familiarize yourself with a few of the plants from the terrarium-friendly plant lists beforehand and keep your eyes peeled.

There are in fact whole enterprises geared towards selling terrarium-friendly plants (though not so much in Canada, unfortunately); in the USA, Black Jungle, Josh’s Frogs and Glass Box Tropicals are three that are very popular amongst dart frog hobbyists, who build elaborate natural planted enclosures for the species they keep in captivity. Not all of us have access to these places, of course, but their stock lists do serve as a handy reference for plants amenable to the terrarium environment.

A couple tips on setting up and maintaining a terrarium: first, use good quality soil for your terrarium and I guarantee better success than using the dirt from the garden centre (I’d written a little bit about terrarium soil near the bottom of this post): one that allows better aeration and increased longevity will make plants much happier over the long term. And keep up on your watering, but notice that a little water will go a long way; one of the benefits of a clear container is that you can watch the water you apply migrate and spread out into the soil. Do this once or twice while paying attention and you’ll get a sense of how much water it will take to keep things just right. And if you’re a heavy-handed waterer by nature, do not despair; there are plenty of plants that don’t mind wet feet. Plants sold for aquariums, for example, are often riparian species that will do marvelously planted in consistently moist to wet soil and kept humid, and the selection in the trade now is better than ever.

Second, keep that thing out of direct sunlight, especially if it’s without any ventilation holes; if you’ve ever been in a greenhouse on a sunny day you’ve experienced the greenhouse effect, where heat is trapped and accumulates within. This effect works within the terrarium, too, and plants inside can easily be cooked if temperatures are allowed to become extreme. If you’ve picked the right plants, bright indirect light should be the most you’ll need, and many will tolerate deep shade fairly well.

Third, do your homework! If you learn a thing or two about a particular plant’s origins and habitat you’ll be able to make an educated decision on whether it’s a good candidate for the terrarium or not; a simple search online with the species name appended with the word ‘habitat’ will bring up a fair amount of information in most cases. Even cultural tips such as ‘enjoys high humidity’, ‘keep out of direct sunlight’, and ‘keep moist but not wet’ are all valuable clues to the suitability of the prospective species. Knowing your plants a little better also increases the richness of keeping them as a hobby, I feel, so don’t be afraid to nerd out a little.

If you are hellbent on succulents and not having much luck with them inside glass containers, perhaps a dish garden may be a better direction to go for your diminutive landscapes; this will allow for better air movement and the option for higher light in order to achieve greater success with these plants. And of course all of this is not to say that a succulent terrarium is impossible; I’m sure there are people out there who can pull it off (long-term, I mean; anyone can stuff some plants in a jar and put a photo of it on the internet). But the terrarium environment is really best suited to tropical species which will respond positively to those conditions, and if it’s the particular form of succulents that appeals to you, there are many other plants which are succulent-looking in nature but which do hail from tropical forests. Many Peperomia are quite succulent, and most are very well-suited indeed; P. prostrata above has to be one of my all-time favourites. There are some caudex-forming epiphytes such as Mymecodia and Hydnophytum (which are profoundly interesting in their own right due to their mutualistic relationship with ants in nature; read more about that here) which are delightfully rotund at the base and often a little spiny, Cryptanthus and other bromeliads certainly conjure the rosette forms of Echeveria or Haworthia, and the list goes on and on, so give something new a try and have another look at the terrarium; there’s so much out there waiting for you.

Epiphyllum oxypetalum, grown here epiphytically on a date palm, and showing a huge flush of flowers that can reach nearly a foot wide. Image © Kiwoncello; image retrieved from Compagna del Giardinaggio.

A small colony of young Sinningia pusilla, growing comfortably in a 2" nursery pot, with blooms nearly the size of the plants. Image © In Situ Plants

Columnea microphylla being shown at a Toronto Gesneriad Society meeting. Image © The Toronto Gesneriad Society; image retrieved from their website.

Stapelia gigantea, shown here with a ridiculous amount of huge stinky flowers. Image © gardenmaniac; image retrieved from the Dave's Garden website.

Lepanthes telipogoniflora, a tiny species with a huge name and a huge flower. Image © Thomas; image retrieved from the Species Specific forum.

What follows below is a short list of several species that have a wonderful aspect to their morphology; they just happen to have ridiculously large flowers, either in fact or in proportion to themselves (perhaps it’s the same as in ants and other smaller creatures, which are able to lift many times their own body weight, that only smaller plants can grow a flower that is larger than the rest of the plant). These are all species that can be grown indoors, though some are more challenging than others.

Epiphyllum oxypetalum and related species

One of the many plants with the common name ‘queen of the night’ (and also known as ‘orchid cactus’ ‘Dutchman’s pipe cactus’ or ‘night-blooming Cereus’), E. oxypetalum is an epiphytic cactus native to Mexico and a good part of Central America. It produces dinner-plate sized white flowers that open for a single night and are heavily scented. This plant grows easily enough in a pot or hanging basket, and will bloom well enough indoors if care is up to snuff. It is pretty rambly by nature, and can get awfully large if you give it room, though it is easily pruned to shape, and at least the stems are spineless, which makes brushing past one in a tight space not as uncomfortable as it might be with some of its close relatives.

Sinningia pusilla

I know that terrarium gardening has been a fad of late, but I fear that the concurrent popularity of succulent plants may cause people to be frustrated by limited success with terrariums (this being for the simple fact that succulents by their very nature are not good candidates for terrarium culture); more on that whole thing later, but in the interest in promoting terrariums as an actually quite easy way to grow plants and have them do well (read grow well and flower), I would like to make Sinningia pusilla the poster child of terrarium gardening.

This species has everything to recommend it; they are adorably tiny (leaves are around 3/8″ long), have fuzzy, somewhat iridescent foliage, and, best, throw huge (relative to the plant, at least) pale tubular flowers. They self-pollinate and are quite prolific, able to quickly start colonies of seedlings that form an attractive ground cover. They also are quite easy to grow if provided with one thing above all: humidity. Enter the terrarium; given the added humidity, these plants will flourish when the soil is kept reasonably moist; if allowed to dry too far or too long, they will go dormant, reducing themselves to a tiny tuber to await the return of more favourable times. They are also fairly undemanding of light, which sets them worlds apart from succulents and other plants commonly toted for terrariums.

Columnea microphylla

This species and S. pusilla above both belong to the family Gesneriaceae, which contains a great many species well suited for growing indoors, of which the ubiquitous African violet is a familiar one. Columnea is a large genus with much variety, but Columnea microphylla has to be one of the most impressive. Again, it is not the largest plant (the one to the left looks like it’s in a 3″ pot), but the red flowers absolutely dwarf the leaves.

This species makes a great hanging basket plant, and the pendant stems will trail downward and show off their freakishly large flowers. This one will need a fair bit more light than the Sinningia above to bloom well, but won’t take up much space in a sunny window.

Stapelia gigantea

A first glance of the foliage and you might want to call this one a cactus, but not only is it not one of those, in fact its more familiar relatives are Hoyas, the tropical vines native to Asia commonly grown as houseplants, as well as the common milkweeds here in Ontario which are the chief food supply for monarch butterfly larvae. Stapelia is a genus restricted mostly to southern Africa, and so need a cooler rest period over the winter. making them a good candidate for a bright but poorly insulated bay window in a century home, say. The flowers can be up to a foot across, but have the unfortunate characteristic of reeking of rotting meat in order to attract flies, which are their natural pollinator. A beautiful plant to be sure, but I suppose not for the faint of heart; perhaps I should recommend that this one be brought outside in summer.

Lepanthes telipogoniflora

I’ve saved the best for last, and this little one is, to me, one of the most incredible orchid species out there, despite being only a couple inches across.

Lepanthes telipogoniflora is a diminutive orchid endemic to Colombia, where it grows in some of the wettest rainforest on earth (one spot once reported 43 FEET of rain in a year), which gives us a pretty fair hint as to how it should be kept in cultivation. Alas. I have personally killed this plant (twice); it understandably does not take to drying out in the slightest, and small plants are completely unforgiving. Enter again the terrarium; many people grow this plant successfully in those little round glass hanging terrariums that are quite easy to find these days, and as long as they’re kept happy (you’ll know it is so because the plant won’t be dead) they will bloom pretty consistently, with the flowers being relatively massive and at least the size of the plant in younger specimens. Another important cultural note is that they, as are many of the Pleurothallidinae orchids, are intolerant of hard water, and require rain or otherwise filtered water to do well. This species is, so far as I know, not produced by any Canadian orchid nurseries (presumably because of the aforementioned cultural challenges), but is brought in by Ecuagenera when they attend regional orchid shows here, and presumably by others as well.

This list of huge bloomers is by no means exhaustive; in fact, I’m sure I’ve only scratched the surface. If any other plants fit the bill, list them in the comments below!

If you’re unfamiliar with the chemical reaction above, then you may also be unfamiliar with the fact that life as we typically tend to think of it would not be possible without plants.

Photosynthesis is responsible for the capture of solar energy that in turn powers nearly all life on earth: everything we eat is either plants, or other animals that formerly ate plants (or that ate other animals that ate plants). Plants absorb sunlight and convert it into chemical energy which is stored within the plant for its own uses; we eagerly exploit this by consuming them and thus the sum of the solar energy they’ve stored. Good deal for us, bad deal for the plants (not that they seem to care).

There are not many other ways to capture and metabolize energy in this way, save chemosynthesis (which is why I need to keep referring to ‘almost all life’ above, which, while definitely less dramatic, is more accurate, as there are organisms which are able to capture energy from chemical reactions, most notably in deep-sea communities colonizing hydrothermal vents, and so have no need of sunlight). So plants really are the foundation of nearly all life on the earth.

And not just regarding energy, either. Though a bit more oft-toted, the fact that plants maintain the planet’s oxygen levels is equally prevalent. This does bring up the subject of conservation, but I can save that for another time. I will add in a shameless plug, though, that plants indoors will raise local oxygen levels and just generally improve the air quality indoors. You can read this post for more information if you like: Plants at Work: The Science Behind how Plants Improve Life Indoors.

For anyone interested in the equation who doesn’t understand the chemistry, basically the plant takes 6 molecules of carbon dioxide and 6 of water, and splits these to create free oxygen (which is released by the plant), and a few other goodies which combine with the solar energy captured by the chlorophyll in the plant to create carbohydrates (the C6H1206 in the equation above) which contain that solar energy. Pretty simple, but critical to life on earth.

It’s a little humorous to me that our industry (speaking very broadly here, of course) provides, in a manner of speaking, a product that no one can live without. Maybe that’s why everyone tends to like plants so much: I’ve met many people indifferent to them (and have changed a few minds there), and many more people who love them but can’t seem to stop killing them (and I can only hope I’ve helped a bit there), but have never really met anyone who’s said that they actively dislike plants (except maybe recent victims of poison ivy or the like). Maybe it’s a stretch to assume that we as a species are that aware of the inexorable connection we have with the rest of life, but for whatever reason the biophilic instinct is certainly alive and well.

High-quality peat moss: note the large, fibrous-looking pieces. This is Lambert`s AFM soilless mix. Image © Lambert; retrieved from their website.

Low-quality peat moss: a photo of the dark, small-particled stuff that is sold at the consumer level. Image © unknown; retrieved (strangely) from LA Readers blog.

It's pretty tough to dispute the effect of a perched water table when it's captured in photos like this. Image © unknown, retried from The Garden Professors Blog

I had promised back in one of the parts of Watering 102 (see parts one, two and three of that massive tome here) to write a little about growing media, and how to select or make one yourself in order to grow great plants. There are several aspects to consider that will help you make the best choice as far as what to use, and a lot depends on the type of plants you grow, how heavily/frequently you water, and environmental factors such as heat and humidity.

We’ll get this out of the way first, though: don’t ever call it dirt. Dirt is the stuff that ends up under our fingernails, and what we sweep off the floor. It’s something of a derogatory term, I feel. This is actually one of the first things that got drilled into us at horticulture school, and it stuck. We are all better off calling it soil, though even this is a bit of a misnomer, as what we typically use for indoor applications is a soilless growing media containing mostly organic material and no true mineral soil, such as you’d find in your backyard. ‘Soilless growing medium’ is a bit of a mouthful, though, so soil will suit our needs here.

First and foremost is peat moss. This material is partially decomposed sphagnum moss which comes in varying grades and qualities, and is the major component of most mixes, from the dusty garbage they sell you at the garden centre to the tried-and-true stuff used to produce countless acres worth of ornamentals of all sorts. When of an appreciable quality, it is best described as ‘fluffy’, and if you compare qualities side by side, the difference is striking. Quality peat is light in colour and feel and has varying larger particle sizes, which allows for good aeration. It also has a good water-holding capacity without becoming mud when very moist. It is relatively long-lived, though it does degrade over time. The other stuff is dense, with mostly small particle sizes, and is basically a more decomposed version of the nice stuff (being dredged from deeper in the peat bogs from which the material is drawn [the sustainability of which practice may come up in a future post]). It does become mud when you try and water it. It’s basically garbage, because it becomes a real challenge to ensure that a plant’s roots are able to absorb enough oxygen to keep from dying.

It’s important to make sure if you’re going to be purchasing straight peat moss for use in your own recipes that it is buffered: peat moss on its own is highly acidic (and is used as an amendment for acid-loving plants such as plants in the Ericaceae family such as blueberries), and bufffering will raise the pH from 4 or so up to about neutral (7), which is where most species will be best suited.

There is an alternate material to peat moss made from the husks of coconuts, called coir. It also comes in differing types, from roughly chopped husks to finely ground fibres. It is longer-lasting than peat, and also is less hydrophobic, meaning it will more readily absorb water when it is dry, which is handy. One serious issue is with the source of this material: as coir is processed it is often washed in seawater, and unless it is thoroughly cleaned can impart some serious saltiness to one’s plants, with the obvious devastating effect that you might expect. It is important to only buy this stuff from a reputable source (hydroponics stores usually stock it), or to process it yourself in order to ensure it is fit for use.

Perlite is usually the other component in soilless mixes. This is an expanded volcanic mineral which imparts greater aeration and water-holding capacity to the mix. It is not fertilizer, nor is it styrofoam, or anything else I’ve heard it being referred to as. It comes in varying sizes, with larger pieces being used for things like bark-based orchid media. It is admittedly ugly and unnatural looking, and has the bad habit of floating to the top of the container when watered heavily.

On that note, bark and sand are two more materials which can be found in some mixes, also in order to create more room for air in the growing medium. Sand is a bit outdated, but it’s cheap, and can be found in the dirt that’s marketed for cacti and succulents. Bark is more useful, but does break down eventually. Vermiculite is another mineral that is sometimes also used for enhanced water retention and aeration porosity. Other materials in specialty mixes are long-figer sphagnum moss, which is the undecomposed version of peat moss (you’ve probably seen orchids grown in this), and which greatly increases the water-holding capacity of a mix, tree fern fibre (a durable material derived from tropical tree ferns which creates a really nice open mix for things like epiphytes) and charcoal, which has little value past increaasing aeration porosity and its longevity.

So with that out of the way, basically what we’re looking for is a medium that provides the right mix of water-holding capacity to air-holding capacity for the type of plants we wish to grow, and for the amount of water we are applying. A decent basic soilless mix such as Berger’s BM6 contains about 75% peat to 25% perlite, and I’ve grown an extensive array of plants in this without any amendment. It can hold a lot of water if you let it, but it’s also a very good mix for keeping lightly moist, as it does drain quite freely. Again, if you let it go bone dry it will be difficult to rewet due to the hydrophobic nature of the peat, so bear that in mind. A lot of growers of gesneriads advise amending a mix like this to more of a 1:1 peat to perlite ratio, and while there’s definitely no harm to it, I’ve been able to grow most gesneriads I’ve worked with in just the basic mix by simply avoiding overwatering.

If you are heavy-handed with the watering can you may benefit from amending your mix, but there is such a thing as too light a mix as well. With increased aeration comes reduced water-holding capacity, and less than adequate watering can quickly lead to dessication. High temperatures and low humidity can also contribute to a more rapid drying of the media, and in some cases it may even be beneficial to have less aeration porosity in your mix: there are some unforgiving plants which are goners after they dry out even once (you’ll notice that the growing media of most ferns you see available, for example, do not even contain perlite).

How you use the mix will play a large role in how it performs. One of the most important things that needs your attention is that the media loses its functionality when it is crammed and forced firmly into the pot. While it does seem to hold a plant in place very well, this basically reduces all of those nice large spaces between soil particles that would ordinarily hold air, reducing them to a size that is then only capable of holding water. That’s bad news for plant roots, and maybe a bit of a slight to the hardworking folks who spend all that time developing and optimizing their professional growing media for the perfect aeration porosity. Slightly overfilling the container with soil and them watering the plant in gently but thoroughly will do wonders for securing the plant as the soil settles into itself, and the integrity of the mix will be preserved, allowing you (and of course, your plants) to take full advantage of its properties.

When watering these mixes, particularly when the container has been freshly planted, it is best to use a watering can or hose with a breaker in order to keep from disturbing the soil surface: in time, the soil’s microbiology will colonize the media and produce exudates which hold everything together nicely and make it easier to throw water on without having to worry too much about taking the extra time (good news for professionals).

Remember, too, that if you’re using any organic material at all, it will eventually decompose, and the soil will need to be changed. I won’t go into repotting here, but if you seem to have problems that could be explained by overwatering even though you’ve been doing everything the same way for a long while, decomposition of the media may be the issue.

A note on terrariums, particularly ones which actually have half a chance of success and aren’t just a few succulents thrown into a glass bubble because someone saw it on Pinterest (yes, I have a serious hate on for the current terrarium craze; so much so that I’ll likely rant aout it in another post): I want to draw your attention to the fabled ‘ABG mix’, one of a few substrate recipes whipped up by Atlanta Botanical Gardens for plants in their collection. This stuff has really caught on in the vivarium hobby (basically a planted terrarium that houses creatures like lizards or frogs), as it has perfect drainage and very long life, which are two things that can plague a planted glass enclosure. The mix commonly used is as follows:

1 part peat moss (or coir)

1 part milled sphagnum moss (ground or chopped long fiber sphagnum moss)

1 part fine horticultural charcoal

2 parts tree fern fibre

2 parts fine bark

You can have many years of enjoyment with this mix in the warm, humid conditions of a terrarium without it breaking down, and another bonus is that it looks way more natural than a peat/perlite container medium. If you play around with the ratios you can also create a great mix for houseplants that also resists decay and can allow you to go for quite some time without needing to repot due to substrate decomposition.

OK, one last thing about container media that has to do with drainage. There is an adage that many of you have no doubt heard about putting pot shards, gravel, or other material in the bottom of the container before filling with soil to allow for better drainage. This is a useless and counter-productive practice, and here’s why: because of the way water interacts with itself and with soil particles (cohesion and adhesion, respectively), it will not move readily from an area with small spaces between particles to one with large space between particles. The top of a layer of gravel or whatever is pretty much the same to water in soil as the bottom of the pot, so basically all you’re doing is eliminating valuable real estate for plant roots, and potentially creating conditions in which too much water is held in the soil because it’s not draining properly. Use the same medium throughout the container and you will generally have better results.

The photos to the left illustrate perfectly the effect of having a larger-particled substrate over a finer-particled one: the water distributes itself throughout the top layer and does not move into the layer below until fully saturated. The myth of drainage is one of those many things in horticulture that has just been repeated so often everyone thinks it must be true (and have a look at the comments on the page I grabbed the image from to see the type of stubbornness to change that is basically rampant in the scene, professional and amateur alike. This was another of the first things that we learned at school, and we did a whole whack of labs that really drove the point home for us.

So there it is, long-winded as ever. The takeaway points, I guess, are: don’t buy shitty quality soil, don’t cram it into the container, don’t bother trying to improve drainage with other materials, and don’t put succulent plants in terrariums.

A photo of the Atlantic Forest of Brazil, a view of which prompted Darwin's words to the right. Image source unknown; retrieved from Projeto Entre Serras.

The cradle of humankind: the plains of Africa. Image © Gossipguy; retrieved from Wikimedia

`…that the naturalist`s journey will go on forever. That it is possible to spend a lifetime in a magellanic voyage around the trunk of a single tree. That as the exploration is pressed, it will engage more of the things close to the human heart and spirit. And if this much is true, it seems possible that the naturalist`s vision is only a specialized product of a biophilic instinct shared by all, that it can be elaborated to benefit more and more people. Humanity is exalted not because we are so far above other living creatures, but because knowing them well elevates the very concept of life.’

E.O. Wilson, from Biophilia

You may have noticed that we reference and tag a word fairly often here at In Situ: biophilia. Biophilia as a concept was developed by the great Edward O. Wilson, biologist, ecologist and prize-winning author, who used it to describe humans’ innate need for affiliation with other living things. From the plants we have kept in our homes since at least the beginning of recorded history, to the out of work domestic animals we still keep around (there aren’t many professional mousers or herders among them these days, at least from an urban perspective- I’m sure there’s still work in the country), to the way we design our cities and parks, human beings have always surrounded ourselves with other organisms. Here’s another (admittedly long) quote by Wilson, who can put it all much more elegantly than I ever could:

‘I have suggested that the urge to affiliate with other forms of life is to some degree innate, hence deserves to be called biophilia. The evidence for the proposition is not strong in a formal scientific sense: the subject has not been studied enough in the scientific manner of hypothesis, deduction, and experimentation to let us be certain about it one way or the other. The biophilic tendency is nevertheless so clearly evinced in daily life and widely distributed as to deserve serious attention. It unfolds in the predictable fantasies and responses of individuals from early childhood onward. It cascades into repetitive patterns of culture across most or all societies, a consistency often noted in the literature of anthropology. These processes appear to be part of the programs of the brain. They are marked by the quickness and decisiveness with which we learn particular things about certain kinds of plants and animals. They are too consistent to be dismissed as the result of purely historical events working on a mental blank slate.’

E.O. Wilson, from Biophilia

So while at the time the book Biophilia was published (1984), there had been no empirical study on the presence of an innate biophilic instinct shared by all of humanity. Since Wilson’s introduction of the hypothesis, many studies have been done that highlight the importance of proximity to nature and other living things to our mental health (see this literature review for a good discussion on some of the studies that have been done: Biophilia: Does Visual Contact with Nature Impact on Health and Well-Being?). Beyond all this, and at the risk of relying on intuition when so many of our human eccentricities are indeed counterintuitive, it just feels correct. At least to me (biased as I might be). Any client I’ve ever spoken with has always pleased with having plants around, and they often comment on how much better a place feels, which seems like mission accomplished and hypothesis confirmed to me.

But how did all this come about? Rooted in our history the habits may be, but the fact that humanity is itself rooted in the natural world is what has caused our deep-seated need to be surrounded by nature. We are the product of a particular habitat, and to this day we still find space in our urban centres for an approximation of it. Think of practically any city park you can imagine. Open grassy areas, with scattered copses of trees; sometimes a pond, fountain or the like. Maybe something somewhat reminiscent of this?

Our species came to be in just such a habitat, and we still seek these same landscapes for comfort, relaxation and meditation. We select our homes in similar ways: perched atop a hill, overlooking water, with a few trees (not too many) here and there describes some of the most sought-after property available (and indeed will often fetch a hefty price).

Turn now to the indoors, where people have been keeping plants for at least as long as we’ve been recording history. All ancient civilizations have depictions of potted plants indoors in the images they created, and sometimes went through great lengths to cultivate plants difficult to grow outside of their native environment (the Romans were building greenhouses even before glass was invented). It is safe to assume that many of these were functional from a medicinal or culinary standpoint, though the Chinese have cultivated ornamental plants indoors for at least three thousand years. Plant mania swept homes and offices in the 1970s, to an extent that has not yet been rivaled (though what those early pioneers of the interior landscape industry would have made of vertical gardening technology!). The interior landscaping industry was born in this era, and has persisted since.

Said industry has often toted the benefits of keeping plants indoors, primarily from a health and employee productivity standpoint (I went through some of the science that these claims are based on here), and some companies have begun to reference the biophilia concept as another selling feature. They are certainly right to do so, but I doubt that many who belong to these organizations have actually read and understood the ideas behind the concept, and are genuinely interested in fostering the sense of interest and wonder in the natural elements we surround ourselves with.

What In Situ is trying to do (and what we would like to encourage the rest of the industry to try to do) is to create more of those moments when nature really takes us in, where time falls away and we are free to explore with our senses the structure of a leaf, say, or the contrasting textures or colours of different plants growing together, to go on Wilson’s ‘magellanic voyage around the trunk of a single tree’. We wish to recreate the forest edge, viewed from our comfortable place amongst the figurative grasslands of our urban interiors, which draws us nearer, showing us glimmers of the mysteries held deeper within. We want to replicate indoors the richness and splendour that has captivated us as a species forever, has inspired countless works of art, and that still, in the lives we live primarily apart from it, holds a special place in our imagination.

‘Among the scenes which are deeply impressed on my mind, none exceed in sublimity the primeval forests undefaced by the hand of man; whether those of Brazil, where the powers of Life are predominant, or those of Tierra del Fuego, where Death and decay prevail. Both are temples filled with the varied productions of the God of Nature: — no one can stand in these solitudes unmoved, and not feel that there is more in man than the mere breath of his body.’

Charles Darwin, from Voyage of the Beagle

By using new and interesting species, and using familiar species in interesting ways, we hope to satisfy the biophilic instinct by completing indoor environments with the engaging natural elements that have been a part of our species’ evolution since time immemorial. When used this way, plants can create a kind of biotic warmth that tempers the sterility of many modern interiors. I don’t advocate turning every indoor space into a jungle (…): rather, the contrast between our manmade constructions and these natural elements are what highlights their presence and what really makes them come to life. The studies I referred to above seem to indicate that having these elements in sight from any area of an indoor space is the optimal placement, and this is the model that many in the industry use when designing their interior landscapes. It`s sound to me, but I feel it’s only effective if the elements are actually visually captivating: this is why we try whenever possible to use plants that people are not usually familiar with, and that have very unique textures or colours, or some other interesting facet to their biology that creates real interest. We seek to foster a true biophilia, through which we can draw inspiration, comfort and knowledge, secure in the surrounds of our earthly cohabitants.

Tillandsia landbeckii, growing where little else will. Image © Eduardo Vergara; image retrieved from Flickr.

Closeup of a Tillandsia sp., showing trichomes. Image © Josef Špaček; retrieved from Botany.cz

Tillandsia biflora in habitat. Image © Jean-Francois Brousseau; retrieved from Flickr

While I don’t wish to discourage anyone from keeping Tillandsia at home, I think that it is important for people to develop a greater understanding of these fascinating plants in order for them to have greater success in their cultivation; they are not as easy of care as most retailers would have you believe, and some species, despite being common in cultivation, are unsuitable (or at best, very challenging) to grow indoors.

The genus Tillandsia is made up of more than 600 species, which is about a fifth of all species in the Bromeliaceae, which includes other favourites such as pineapple. They are distributed, as are nearly all bromeliads, across North, Central and South America (there is one species of Pitcairnea which made it Africa somehow). There is a large variety of form across the genus, as different species have adapted to widely different habitats, from montane rainforests that are some of the wettest places on earth, to arid coastal deserts that receive a scant 3mm of rain annually, at best, and knowledge of where a species originates is of great use when determining how to care for it.

Cultivators of Tillandsia often lump species into two general categories: grey- and green-leaved varieties. This is a pretty good place to start, in terms of their care; the grey-leaved species are typically from more exposed, sunny habitats, and are evolved to make use of the sometimes very little water they receive in these environments, while green-leaved varieties are typically from more shaded, moister habitats. There are exceptions, of course, and so I reiterate that knowing where a species is from will be give you the best chance at success.

The grey colour is due to the leaves’ trichomes, which can perform quite a few functions in plants, but which in this case are designed to capture airborne moisture such as fog, as well as reflect sunlight (up to 45%, apparently). Species will have more or less of these depending on how water-deprived or exposed its habitat is.

The ones more often in cultivation are typically the grey-leaved varieties (though Tillandsia cyanea is definitely another big player, even if it’s typically sold potted along with all the force-flowered Guzmania and Vriesea bromeliads), and I’ll mention a few things about their different habitats below.

Dry Tropical Forest

Many species inhabit dry tropical forest which sees precipitation for only part of the year. Examples of species include T. brachycaulos, T. caput-medusae, and T. xerographica. As epiphytes, these plants are found at different heights on host trees, where there is good air movement (which allows the plants to dry after rainfall) and varying amounts of sunlight depending on where in the tree a particular species is found (and indeed, different species seem to have different preferences for what part of the tree they occupy). These species, because of their requirement for good air movement, are not particularly suitable for most terrariums (despite what you’ve heard), though they do much better in higher humidity than is typically found indoors. A larger terrarium with air movement via a computer fan or the like (see here for some ideas on how to do this, with the understanding that your own endeavors with electricity in moist environments are obviously your own problem) would probably be best, and indeed that’s where I’m having the most success with plants from this type of habitat. Being hung outside under a tree through the summer months (at least here in Toronto) would probably treat them just fine as well.

A note on the seasonality of these habitats: these forests are marked by distinct dry seasons with little to no rain, during which time host trees may drop all their leaves, presumably exposing any harboured epiphytes to more direct sunlight. There doesn’t seem to be much written on coercing these plants to bloom, but in my experience an increase in light can often do the trick, and may well be the trigger for flowering that the plants use in nature.

There are also many Tillandsia species in cultivation which are from disturbingly arid habitats. These are the stiff, very grey-leaved species that are adapted to take what they can get, water-wise: T. tectorum, T. albida and T. edithae are a few examples of species. I say disturbingly arid because these can be some of the driest habitats on earth: the Atacama coastal desert of western South America, for example, has a few weather stations that have NEVER RECEIVED RAIN. Tillandsia species from the Atacama have evolved to take advantage of the coastal fog that rolls in from the ocean, allowing the plants to capture airborne moisture. Some xeric species inhabit high elevations in the Andes, and take advantage of the clouds that float through their habitats.

These species are much more tolerant of dry air, direct sunlight and restricted moisture, but the converse to this is that they need a lot of sun and also cannot be kept too moist. South-facing windows (or, optimally, a solarium or greenhouse) are probably best in the case of these plants, and they are definitely not suited for most terrariums.

A note here on watering Tillandsia: these plants use CAM (Crassulacean acid metabolism) photosynthesis, which is really neat and interesting and worth talking about at length, but which for our purposes here means that they open their stomata to absorb carbon dioxide at night rather than during the day as do most other plants. Wetting the plants before nightfall can inhibit this gas exchange and in effect suffocate the plants. The xeric plants, at least, receive moisture in their native habitat before dawn, allowing them to absorb carbon dioxide and then liquid water before the demands of the desert day begin. I don’t advocate waking up at 4:00 a.m. for any reason (though maniacal plant care is, in my opinion, a better reason than most), but watering your Tillandsia in the morning is probably best practice. And water them well: aside from the really effective water-catchers like T. tectorum, the oft-recommended misting with a spray bottle isn’t going to do much for the plant: give it a good soaking with a watering can or a quick dunk in a bucket.

Moist Habitats

Though not as common as the ones you find piled haphazardly in a basket at your local florist or garden centre (can you tell that gets on my nerves?), these are my personal favourites. Even T. cyanea, which is pretty boring as far as these go, foliage-wise, is an easy to grow species that does well in a pot. These species are, as far as I know, strictly epiphytic, and inhabit some of the wettest habitats on earth. The aforementioned T. cyanea, T. flabellata and T. biflora are three that can be found with a little digging (some more than others).

Conditions should be moist and humid, but with very good air movement, and lighting can be lower than for species from the previous two habitats I mentioned, so if you’ve been losing plants due to a combination of low light and excessive moisture, you might want to try one of these. T. cyanea is a tough plant, but T. biflora, in my experience, is not, and best results will be had in a greenhouse or large terrarium with good air circulation.

There are obviously gradients to these habitats I’ve mentioned here, and research into what species you have will give you the best idea of how to care for it. A little experimentation never hurts either (OK, sometimes it does), and you may find that some species are quite forgiving in cultivation. The lesson here is that, at least nine times out of ten, your local purveyor of Tillandsia hasn’t the slightest idea of how to keep them alive over the long term (you can even buy them in furniture stores now, apparently: I saw a bunch of mounted ones piled crudely on top of each other in a West Elm store here in town), so you should do your homework if you’d like to have success with this interesting group of plants.

Sporophyte fronds of what I`m presuming is Adiantum peruvianum, doing their thing in one of In Situ's vertical gardens. Image © In Situ Plants.

Just a short one here, but I’m pleased to report that the little gametophytes I wrote about back in June have started to produce their first fronds, AKA sporophytes (being the part of the plant that eventually produces the spore which gifted us with the gametophytes in the first place). Again, I can only presume that these are Adiantum peruvianum, as this is the only fern species in this garden, but there are a lot of other ferns here at the lab (to say nothing of the effectiveness of travel by spore; these ferns really could be from anywhere), and so I’m still not 100%. (And there’s actually a terrarium in another room of the building that appears to be growing something similar, so the plot could still thicken here.)

They’re pretty cute, though, either way. As soon as we start to see more mature foliage on these plants I’ll update again with a more conclusive ID. The plants pictured here are way up at the top of the wall, and should produce a nice (albeit unplanned) cascading effect once they get going (again, presuming they’re even A. peruvianum).

We, as an industry, nearly always tote the benefits of interior plants, and I’m here to tell you that it’s not just bullshit: there are measurable effects in the way people think, behave and feel when they are in an environment that contains plants versus one that does not, and plants actually are able to clean the air we breathe.

Instead of doing what everyone else does, which is usually just to concisely (we all know that’s my strong suit, ha ha) list the same key points, I’ve done the legwork and actually rustled up a few of the papers from which said points were drawn from, and will point you to them so that you can read for yourself the results of some of the various studies that have been conducted over time.

By all means be skeptical, and don’t take our word for it: we’re very few of us scientists in this industry, but there has been real scientific work done which really confirms what we’ve been saying all along: that plants indoors have a direct effect on things like employee productivity, reduction of airborne pollutants, and combating stress and fatigue.

Cleaning the Air

So for starters, do plants actually clean the air? It would be a boring blog post indeed if I said no, and here are a few papers which highlight some of the work that different plants (and their associated colonies of soil-dwelling microorganisms) do to remove harmful chemicals from the interior atmosphere. What I’m not going to do is tote the old NASA study that gets thrown around so often: you can look that up for yourself, but Dr. Wolverton (and others) have continued to do good research into this phenomenon since the first study was published in the 80’s.

Plants and Soil Microorganisms: Removal of Formaldehyde, Xylene, and Ammonia from the Indoor Environment

This study found that quite a few plant species, notably Boston ferns, chrysanthemums, and dwarf date palms, were able to remove appreciable amounts of these chemicals from the air inside sealed chambers. Based on prior research into indoor air pollutants by the EPA, the authors calculated that an average-sized office constructed of typical building materials would contain 3916 µg (micrograms) of formaldehyde (to use the most sinister example in the paper). A single Boston ferns was shown to remove 1863 µg of this formaldehyde- per hour! The mums and palms were not far behind, and there was a decent list of other plants which were also quite effective at removing formaldehyde from the air.

Figure 1 from the study linked above, showing formaldehyde
concentrations being removed by a Boston fern. — Figure 1 from the study linked above, showing formaldehyde concentrations being removed by a Boston fern.

The other part of the study looked at the microorganisms which colonize the rhizosphere (the area immediately surrounding plants’ roots), and the role they play in the removal of these chemicals. They found that unsterilized soil was able to remove formaldehyde from the air while sterilized soil was not, and that soil containing a plant was more effective still. They found that different types of bacteria had an effect on how much formaldehyde was removed, and the data indicated that different plants harbour different types of soil bacteria. Check out the paper for yourself: I’ve linked to it above.

Purification Ability of Interior Plant for Removing of Indoor-Air Polluting Chemicals Using a Tin Oxide Gas Sensor (sic)

This study performed similar experiments to the one above (you can read it yourself for the full details), with a slightly different method. Their results were similar: plants and their associated bacterial communities removed airborne pollutants quite effectively from the atmosphere. One point of note is that temperature and light had a large effect on the experimental results, suggesting that plants are more effectively cleaning the air when they are actively growing (see the portion in the discussion on uptake of gases through stomata if you like), which really bolsters the case for optimizing plant health in the interior landscaping in order to maximize this beneficial effect.

Improving Employee Productivity

This is a claim that is often used because it seems to infer a real economic benefit to the client. I’m inclined to agree with the science, and I can see that this certainly makes interior landscaping more marketable, but it almost feels like a bribe: surely plants can be desirable of their own merit, and surely the effect they have on people should not be measured in terms of productivity but of general mental and physical health? Do clients actually purchase plants to get more out of their staff? At any rate, the effect has been measured in the following papers (and I’m sure there are more); let’s call it here just an added bonus to the addition of plants to the workplace.

Interior Plants May Improve Worker Productivity and Reduce Stress in a Windowless Environment

This is one of the commonly cited ones, in which the authors noted a 12% increase in productivity (measured as reaction time to a computer task). I’m not sure that this is really a rock-solid study, and I wish I could have found another paper which replicated the experiment, but it’s here, for what it’s worth. One more interesting point in the study is the result on the blood pressure of the participants, which measured significantly lower during and after completing a computer-based productivity task in participants in a room with plants versus that of those in a room without.

Effect of Ornamental Foliage Plants on Visual Fatigue Caused by Visual Display Terminal Operation

I’m hoping that someone’s Japanese is better than mine and they might comment on this paper, but based on the English abstract and the figures in the results, these researchers found that viewing plants while performing tasks on a visual display terminal (presumably a computer screen of some sort) resulted in reduced visual fatigue when measured as critical flicker fusion frequency (a somewhat complicated phenomenon that you can look up on your own). I can’t comment much on this one, as I can’t even read it, but the numbers are there.

Plants Enhance Productivity in Case of Creative Work

This is more of a press release than an actual paper, I think, but it highlights the results of an experiment carried out by researchers in The Netherlands, which found that, while no improvements to productivity tasks were noted, there was a marked improvement in performance of creative tasks. These improvements were even more dramatic with test subjects with self-reported stress or exhaustion (the study used students as their guinea pigs)

In Situ Plants interior landscapes, vertical gardens, and other plant installations in Toronto — Figure 2 from the productivity paper above, showing the number of correct associations by students who reported a high level of physical exhaustion.

General Health and Wellbeing

This is probably the most important one for me, because it has much to do with the concept of biophilia, which I will be addressing soon (likely at great length), and which is tied very closely to In Situ’s raison d’être. We believe that humans have an innate subconscious need for proximity to natural elements, and keeping plants indoors proves to be a noteworthy way of satisfying this in our modern urban settings.

General mental health seems a difficult thing to quantify, but the works below are able to convey a few measured benefits to having plants around us while spending, as we typically do, the majority of our time indoors.

Stress Recovery during Exposure to Natural and Urban Environments

This almost creepy lab study measured several parameters (heart rate, muscle tension, etc.) during and after showing the poor participants videos of people getting into violent industrial accidents, followed by a video of either a fast-moving stream, a wooded area, or varying degrees of busy vehicle or foot traffic. The results clearly showed that the wooded scene was very effective in recovery from the stress indicated in the physical tests.

The self-report from the participants also indicates that the nature scene was the most positively affective by far, and best able to reduce anger, aggression and sadness.

Greening the Great Indoors for Human Health and Wellbeing

This extensive study looked at various aspects of how keeping plants indoors relates to human well-being, from mental and physical standpoints. In section 5, the authors had their subjects complete Profile of Mood States questionnaires (apparently a widely accepted method for measuring different psychological states) before and after the placement of varying numbers of plants in their workspaces for a period of three months. The questionnaires covered such feelings as tension/anxiety, fatigue, and confusion.

The data shows that plants did in fact affect these parameters, and that the control group with no plants scored even worse on the questionnaire than it initially had done, while the subjects with plants saw their scores improve markedly.

The Role of Nature in the Context of the Workplace

This is also mostly a literature review, and includes quite a few statistics from other authors’ papers (which is why I’ve included it here), but the author points to two of her own studies, and I’d like to summarize here the gist of the second one: in a survey rating employee satisfaction, the availability of a view out of doors was considered far more valuable and restorative if it contained natural elements, and became even more so the more natural elements could be seen. Further to this, respondents with clear outside views to natural elements reported feeling more positive about their work in general. From the above:

“These results point to the range of impacts that a view of nature can affect. Those with a view of nature felt less frustrated and more patient, found their job more challenging, expressed greater enthusiasm for it, and reported higher life satisfaction as well as overall health.”

Pretty interesting stuff, I think. It will be interesting to stay on top of the science and see what further studies come from this quarter. If anyone has any further information on this they want to share (for or against, of course, though I bet you’d be hard pressed to find a study against plants in buildings), be sure to include it in the comments.

Tag: garden

More Thoughts on Variety in the Interior Landscape

Thrips: A Tiny but Noteworthy Pest of the Interior Garden

Beyond Succulents: Strategies for Successful Terrarium Gardening

Freaks of Nature: A Few Plants with Disproportionately Large Flowers

Why You Can’t Live Without Plants

Bags of Dirt: How to Choose a Growing Medium for Interior Plants

On Biophilia and the Value of Interior Landscaping

Some Notes on the Natural Habitat of Tillandsia spp., and Inferences Therefrom on their Care in the Interior Environment

Ferns from Scratch, Part Two

Plants at Work- The Science Behind How Plants Improve Life Indoors