vertical garden Archives - In Situ Plants Toronto | Green Walls | Live Walls

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.

Figures 1 and 2 from the bedding plant study linked above, showing increased flower production and less wilting in plants grown with less available phosphorus.

Remember, the job of the fertilizer company is, first and foremost, to sell fertilizer. Properly managing plant nutrition is the responsibility of the grower.

I can’t dispute that phosphorus is an essential element in plant growth: it is present in every cell, and is directly involved in many processes in the plant, including, energy generation, respiration, nitrogen fixation, and most importantly photosynthesis. A plant can’t do much without it. There are a lot of old ideas, though, that are repeated in the horticultural industry, despite the fact that they have been obviously disproven. In the interest of attempting to dispel the dogma and disseminate some valuable insight about how plants actually make use of the phosphorus that we provide them (or, more importantly, how they often don’t), what follows are a few points that hopefully will help professionals and amateurs alike choose the best fertilizer for the needs of their plants.

Note that I put the word ‘interior’ in the title, hoping to imply that the plants I’m discussing are growing in a soilless growing mix indoors, and not in the ground: that’s a whole other can of worms, and the concepts here will be greatly simplified without having to worry about it. We’re working with basically a blank slate here, nutrient-wise. It’s also easier for us here in Toronto because the water is fairly low in minerals save the bloody bicarbonates, which I’ll likely talk about at a later time.

The phosphorus used in fertilizers for the most part is derived from rock phosphate, which is becoming more scarce with time (here’s an article that discusses a few aspects of that whole thing as it pertains to global agriculture: Phosphate: A Critical Resource Misused and Now Running Low). There are other sources, notably from organic sources such as bonemeal and bat or bird guano, which can be combined with a growing media and which makes itself available to plants gradually and thus acts as a kind of organic slow-release fertilizer for plants.

As mentioned above, phosphorus is one of the macronutrients that are required for healthy plant growth (as opposed to the micronutrients, which, while also essential, are required by the plant in much smaller quantities). In most fertilizers, the three primary macronutrients are listed on the packaging as a ratio in the order of nitrogen, phosphorus and potassium, such 20-10-20 and 15-30-15. These may or many not have the additional macronutrients calcium, magnesium, and sulphur, as well as the fairly long list of micronutrients. In most fertilizers that you can buy ‘over the counter’, so to speak, the amount of phosporous will typically be equal to or greater than nitrogen or potassium. There are several reasons why this is ridiculous.

Plants do not use most of the phosphorus that is contained in these typical fertilizers. These high-phosphorus recipes have their origins in field crop production, where phosphorus behaves quite differently than in our soilless media, and where yields can be significantly affected by the availability of this nutrient. Producers of fertilizers for domestic use typically market high-phosphorus fertilizers as producers of better root growth and better blooming, when in fact the extra fertilizer is of no use whatsoever. They make quite a killing at it, too, I’m sure. It’s pretty wasteful, though, as it happens, and it seems that, at least in some cases (see below), lower phosphorus can produce better flowering and better quality crops in general.

Additionally, the fact that the extra phosphorus doesn’t leach away and remains present in the soil can have some negative effects: too much can inhibit the uptake of other negatively-charged elements such as iron and manganese. It also readily precipitates with other elements, forming insoluble compounds which are unavailable to plants, such as calcium and magnesium phosphates, particularly at higher pH levels.

But so how much phosphorus do plants actually use? Not very much! This paper provides a good look at the use of phosphorus by azalea plants, and indicates that the addition of phosphorus above a certain (low) threshold made no significant difference to the growth of the plants in the study: Nitrogen and Phosphorus Uptake Efficiency and Partitioning of Container-grown Azalea During Spring Growth. And here’s another paper that shows that lower phosphorus levels can actually produce better quality crops, with more flowers that held for longer time, as well as increased drought tolerance: Improving Bedding Plant Quality and Stress Resistance with Low Phosphorus.

So from these and other studies, we can determine that phosphorus seems not to promote better blooming, yet somehow these fertilizers can seem to be effective, hence their continued use. What is it about them that makes them work? The answer is in the number to the left: nitrogen. Many of the ‘bloom booster’-type fertilizers have either reduced nitrogen or increased phosphorus/potassium levels, and a reduced nitrogen to potassium ratio is one of the ways to shift plants more into reproductive mode, wherein they obviously produce more flowers at the expense of foliar growth. Balancing plants between vegetative and reproductive growth is the art of the commercial grower, and it is a fine art indeed, and worth examining to the amateur grower.

Recommendations for commercial crop production of most tropical plant species (which, to be fair, are mostly grown for their foliage) is for the use of a fertilizer with a 3-1-2 ratio, though even this seems a bit high: compare it, for example, to the MSU orchid fertilizer, which is 13-3-15, and which is a fantastic recipe, in our opinion. This article from the American Orchid Society discusses some of the reasoning behind the ratio they use, and how it works to create beautifully balanced plants that grow and bloom at an optimum: Without High Phosphorus A New Fertilizer Proves Itself with Orchids. It’s important to note that this fertilizer was not developed specifically for orchids, but is rather a well-suited mix for plants of any type, being built on sound principle and good science. For those in the business, or those who really go through the stuff, it would be fairly easy to reverse-engineer it from the guaranteed analysis on the label if you have access to the raw materials. (A hint if you don’t want 200 lbs of elemental fertilizer sitting around- hydroponics stores often sell smaller bags of potassium nitrate, etc., though for an inflated cost.) If anyone is interested in doing this and doesn’t know how, say so in the comments and we’ll see if I can’t help you sort through it.

I find it a little funny that even though the recommendations for production are to use a 3-1-2 ratio, I see professionals further down the line such as interior landscapers or garden centres using something like 20-20-20 (or even 10-52-10 for new transplants). Phosphorus is about four times more expensive than it was ten years ago, and I don’t presume the cost will be going down any time soon. Given the plants aren’t using it, why throw your money into the dirt, so to speak? Even local orchid societies are applying high-phosphorus fertilizers to their collections, despite vendors at their meetings carrying the MSU feed! Old habits die hard, I suppose.

I’m not recommending that anyone rush out, buy a reverse osmosis filter and start mixing up batches of MSU feed to start doing their houseplants (well, I sort of am, though it is expensive and maybe almost as wasteful as the extra phosphorus I’m bitching about here, due to the waste water that RO filters produce- your plants would love you for it, though, particularly those that struggle with the ever-present nasties like flouride [like, say, every Dracaena], and with high total dissolved solids in general [like some orchids and most carnivorous plants]). But it is worth considering when choosing or mixing your own fertilizers. There are a lot of ones that you can find on the market that are in and around the 3-1-2 ratio (particularly if you’re not looking at the major brands, which have got a good thing going with their ‘root-‘ and ‘bloom-boosters’), and you can give yourself a pat on the back for having used less of an increasingly scarce fertilizer. You may also save yourself some nutritional problems down the road. And if your plants aren’t blooming as well as you’d like, there are other avenues to experiment with besides lowering your nitrogen (though it will probably help), like lowering your night temperature a little (tricky out of season, unfortunately), giving the plant more light, or reducing somewhat the amount of water you give it, all of which are known to promote reproductive growth. Some plants won’t even set buds until some triggers are hit, like shortened day length or extended drought. Another reason to know what you’re growing, I guess.

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.

Utricularia australis, which prefers to grow on the wetter side of wet. Image © Josef Hlasek; retrieved from his website

How Much Water?

Once a schedule (see the last post) is in place that allows you to maintain better constancy in your soil moisture, you can now tailor the amount of water you apply to different plant species. There is no plant I know of that does not appreciate water, unless it is in dormancy. The issue is with the amount of water, and thus the amount of air, that is in the soil at any given time. Most cacti, for example, are evolved for long periods of drought, but this doesn’t mean that this is their preference. So often certain plants are described as ‘needing to dry out between watering’, but the truth is that this is not the case: rather, the plant needs to be prevented from ever becoming too moist for too long. Maintaining a very light but consistent level of soil moisture will allow xerophytic plants like cacti to maximize their growth without causing damage to the roots. This requires something of a steady hand in order to not give your plants too much water, and adapting your soil for different species can help a lot to get things perfect (in the case of cacti and other succulent species, I recommend adding something with a large particle size that improves the aeration porosity of the soil). It is worth noting, though, that with careful watering alone, you should be able to keep widely different species in a standard peat/perlite mix.

Knowing which species you are caring for is the first part of knowing how much water a given plant will need. There are countless resources online and elsewhere that recommend care for the majority of species in circulation. If you’re more inclined to nerdiness like me, you’ll also probably look into where the plant originates in order to learn more about its natural habitat, and take cues from this towards the plant’s care. (I will write more on this at some point; I promise.) All this, though, needs to be tempered with your own experience of the plant and how it grows in your environment, and this requires that you pay attention to what your plants are doing, and how their environment changes throughout the year. Some species are known to rest a little through the winter, for instance, and typically these do not require much moisture at that time. Conversely, the air generally becomes much drier indoors during the winter, when we run our furnaces, which may contribute to the plants’ increased respiration and thus need for additional water. Your growing situation is unique, and it is up to you to find what works best.

Some plants prefer a moist soil, and yet do not take up too much of the water, so after obtaining the correct level of moisture, one can apply small amounts to compensate for the plant’s uptake and any loss through evaporation. One the other hand, some plants which prefer moist soil use a tremendous amount of the available water, and so will need to be watered heavily on the regular. Plants receiving more light will use more water than those in shadier spots (and will require more feeding, but this is best left for another time). Larger plants will obviously use more water than smaller ones, though larger plants are often more drought-tolerant than smaller ones.

A quick note on watering until water flows from the bottom of the pot: unless your water is of very poor quality or you are feeding large amounts of fertilizer, this practice is not really necessary. It is a good way to ensure that your soil becomes evenly moist (read saturated), and it is definitely helpful to have drainage in the event that you do overwater, but it is also a waste of water. In our industry we keep plants for many, many years in containers which do not drain, and they fare quite well. Another aspect to this is that if soil is completely dry, often the applied water will travel straight through it and out the bottom of the pot without wetting anything along the way, which can give a false sense of accomplishment if all we`re looking for is water pouring out from the bottom. If your soil is already a tiny bit moist, simply water carefully (read slowly) until you bring the soil to where you want it, moisture-wise, and you won’t need to waste any water.

Quantifying (sort of) Soil Moisture

So I just spent a whole bunch of paragraphs explaining that different plants prefer different levels of soil moisture, often at different times. But what does barely moist or nearly wet actually look and feel like?

Enter the squeeze test. In most quality peat-based media (not the off-the-shelf stuff), the soil will dry to a conspicuous pale tan colour. If the soil is completely dry, take a handful and squeeze it and it will not hold together. A slightly moist soil will be slightly darker and will mostly hold its shape if you squeeze it as above. Moderately moist will be darker still, and should hold together and even release a tiny bit of moisture if squeezed. Moist and saturated soil will be as dark as the soil can get, with some and quite a bit of water, respectively, released upon squeezing.

This squeeze test is a good way to familiarize yourself with how much water is in the soil in relation to its appearance. Once you get a feel for it (ha ha) you will be better able to eyeball the moisture level of the soil more accurately, though relying on appearance alone can sometimes be deceiving (more on this in the third part).

If a plant wants to stay moist but not wet (and many do, but please don`t accept the care instructions that come with purchased plants as gospel, for there are quite a few variables I’ve already mentioned [and more that I haven`t] that can affect how much water a plant uses), keeping it between moderately moist and moist will likely keep it happy. Keeping a soil barely moist, as I mentioned above, is a great way to optimize the soil environment for succulents or similar plants. And then there’s all of the in-between.

You will need to make your best judgement as you work with soil moisture levels based on your growing environment and the species you’re working with. Don’t be afraid to experiment, but make your changes incremental as you pay close attention to the plant in order to draw useful conclusions and avoid issues.

One more thing I think I should note before I leave off: you’ll notice that I keep (almost exhaustingly, probably) using the word soil, and I should clarify that when I say this I am referring to whatever you’ve got your plants growing in (which I hope is a high-quality peat-based growing medium), and not that heavy mineral stuff from the back yard. These high-quality growing media are referred to as soilless mixes for the fact that they do not actually contain proper soil, but for our purposes here the term soil will be used (in part because it’s shorter and I seem to be typing it an awful lot).

I’m going to follow this post with one on Ways to Tell if a Plant Needs Water next week.

A photo of a sopping wet rainforest which I've put here instead of a boring stock image of someone watering a houseplant. Bosque Protector Los Cedros, Ecuador. Image © In Situ Plants.

The Moisture Release Curve, showing how water is available (or not) to plants. Image © Dr. Heiner Lieth; Retrieved from his page on the University of Caifornia website.

Watering is perhaps the greatest challenge people face when keeping plants indoors: getting it wrong can prove disastrous for many species, and it can be frustrating to lose a plant. As professionals, we are often asked how much water a plant needs, how often it needs it, and how to tell if it’s too much or too little.

I can’t give you all the answers: every plant is different, as is every interior environment, and both plants and their environment can change quite often. I can, however, outline (in a long-winded, but hopefully informative way) a few principles and techniques to help you answer these questions for yourself so that you can have greater success keeping plants indoors. This is Watering 102 because there are some more complex ideas here than are covered by other watering articles online for those that really want to nerd out about it.

After having finished this first bit, I’ve decided to release this guide in three parts, as it’s become almost absurdly long and you’ll probably want a break in between. I apologize in advance for not having kept it all more concise; please let me know in the comments if anything needs clarification. Today’s tome of a post covers irrigation frequencies and the moisture release curve of growing media. Don’t be scared.

How Often Should I Water?

Irrigation frequency is a something of a complicated subject, as there are many factors at play. Some plants need more or less water than others, and these needs can change throughout the year. What follows are a few considerations to keep in mind as you decide for yourself how often to water your plants.

From an industry standpoint, many professional companies, in the interest of reducing labour spent on maintenance, visit their plants every two or even three weeks. (There are some that go even longer, but they either do a horrible job or else make use of sub-irrigation technologies to ensure plants have access to water in the interim.) At In Situ, we typically visit our plants once a week. (Just sayin’).

The reasons for doing this are many, but an important one is to ensure that our plants make the best use of the water that is applied. We are typically maintaining larger plants than those often found in homes, but unless your plants are very small (4” pots or smaller, say), your space is especially warm or dry or the plants are in direct sun, weekly is probably a safe bet, or at least a good place to start when creating a schedule. Pick a day where you know you’ll have the time, and stick with it.

Note that when I said above that we water once a week (typically) in order to aid the plants in making the best use of the water we apply, I did not say that we necessarily apply more water than if we were to water every two weeks. In fact, the chances are that we apply less water over a two week period in two doses than we would do in a single dose. This is because soil that is still slightly moist can reabsorb water better than one that is bone dry. Peat moss (the main ingredient in most growing media), when dry, is hydrophobic, and actually repels water: we’ve probably all tried to water a plant and had the water glance off the soil and fly out of the pot and onto the floor, right? Never allowing the soil to completely dry allows one to apply only a minimum of water in order to bring the soil to the desired level of moisture, without having to rewet all the peat every time, which usually leaves it saturated, which can be dangerous.

Other sources may tell you that watering on a schedule can be bad for plants, and that the best thing is to ‘water when the plant needs it’. Watering exactly when the plant needs it is great if we have little else to do but hover over our plants with a watering can all day. Watering on a schedule can be bad if you are just blindly applying the same amount of water every week, say.

Watering at regular intervals, though, can allow one to monitor the plants and to see what the effect of the last watering has been. For instance, if a week has passed and you check your soil to find that it is still very moist, chances are that you probably applied a bit too much water the last week, and you can ease up a little going forward. Likewise, if you discover a very dry soil (and hopefully not a wilted plant!), you can probably begin applying a little more water every week. Plants’ needs can change from week to week as well, due to the weather, whether the plant is flowering, etc., and so we need to take this into account when we do water.

Most potted plants (as opposed to those in hydroponics or the like), cannot take up water from saturated soils, because the extra water has displaced all the gases in the soil, primarily oxygen. This interferes with the normal growth of the plant (part of which involves taking up the water from the soil) and also causes roots to die, having been, in effect, suffocated.

Plants that are watered infrequently typically need a large amount of water applied to ensure that they do not go too dry before they are watered again. The consequence of this is that there is a period immediately after the plant is watered where not only is it not using the water (because it is unable), but it is also not receiving any oxygen to its roots, which can damage the root system.

When a plant is allowed to go too dry (again, another risk inherent in long irrigation frequencies), roots can also be damaged: the obvious way is through desiccation, when root tissues dry out, collapse and die. But there is another danger: when a plant`s soil is dry, roots, in effect, suck harder at the soil to try and take up as much water as they are able (this isn’t technically exactly how it works, of course, but I’m not getting into capillary pressure, vapor pressure deficit, etc. here) to compensate for the water loss from the leaves through transpiration. If a plant is watered heavily at this point (and we`re all guilty of really soaking a plant that has gone too dry, mostly out of guilt), the plant takes up too much water too quickly, and the cells of the roots can rupture and, you guessed it, die. Proper restoration of a plant that has gone too dry involves gradually bringing soil moisture back up to a level where the plant can take it up without damage, which can take several hours’ worth of applying tiny increments of water to be successful. (Best, perhaps, to never let it get to that point, although as an aside I have heard that some plants can respond to drought stress by flowering, Spathiphyllum and Nematanthus among them.) It is perhaps a lot to ask someone to spend half their day watering one plant every half hour, and there are, to be fair, at least a few species which seem not to mind going from bone dry to wet, in my experience. Just be aware that this can be a concern.

The diagram to the right shows an example of a moisture release curve, which illustrates the availability (and unavailability) of soil moisture to plants. In this, case, anything above about 75% and under 20% is pretty much unavailable to plants, and furthermore those extremes can be dangerous to plant root health. So in order to optimize water uptake and keep our root zone healthy, we need to keep the water between (again, just in this hypothetical instance) 20-75%. How do we do this? Water more often!

This is where the weekly watering, as opposed to bi- or tri-weekly, can be a very useful tool. If we apply smaller amounts of water more frequently, we can maintain a more balanced soil moisture level, without the wild swings of ‘feast and famine’ watering. In this way we can keep the plant as close to its preferred level of moisture as possible for as often as possible, allowing the plant to grow its best without periods of inactivity or even stress.

Stay tuned for the next installment; How Much Water, wherein I don’t tell you how much water to give your plants.

The Carboniferous garden: Afrocarpus gracilior, Zamia furfuracea, Asplenium
nidus, Microsorum pustulatum and Psilotum nudum. Image © In Situ Plants. — The Carboniferous garden: Afrocarpus gracilior, Zamia furfuracea, Asplenium nidus, Microsorum pustulatum and Psilotum nudum. Image © In Situ Plants.

Cyclosephala colasi on a Philodendron inflorescence. Photo © Marc Gibernau/Denis Barabé; retrieved from the International Aroid Sciety website.

“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

One of In Situ’s primary goals as a company is to increase interest in plants in order to reconnect people to the natural world. We believe strongly in the hypothesis of biophilia, first conceived by the venerable E.O Wilson; the human need to commune with other living things. We feel as though this is why people have always kept plants indoors, and that now more than ever it is important to continue the relationship.

We use several strategies in order to further this goal of increasing interest in plants: making use of the wide variety of less-often used species is a good example, as the visual impact is immediate and apparent. Beyond plants’ appearances, however, lies the really fascinating stuff, and this is what we like to bring to light in our designs.

Even the most commonplace species can hold fascinating features when they are brought into context. For instance, the humble Philodendron, long a staple of interior landscapers, has a unique aspect to its physiology. The inflorescences (flowers) of many species are thermogenetic: they produce heat. And quite a lot of it, as well: some species’ inflorescences can rise 10°C above ambient temperature! This interesting adaptation serves to volatize aromatic compounds that attract pollinators, of which beetles are usually the primary ones. See here to read more about thermogenesis in plants.

The above is just one example of the countless facets through which one can look at plants. There are many themes which we have explored; below are but a few.

Biotopes

Plants’ natural habitats are, particularly in the case of the tropics, richly populated communities of species, with many growing closely around (or on, or in) each other. These ecological landscapes are referred to as biotopes, and these are interesting themes to explore, as they offer us a (somewhat stylized and selective) glimpse into where these species are from. To actually see these habitats in person is incredible, and we want to share this with our clients. Using solely plants from a particular region can highlight, for example, an area under grave threat of deforestation, highlighting the need for conservation.

Natural Variation within Species

The world of plants is one of incredible diversity, and even within species, an incredible amount of variation can be seen (see this post for more thoughts on this). Another perspective on this variation is convergent evolution, in which completely unrelated species evolve similar forms to solve the same problem. For example, many of the Euphorbia species from Africa and Madagascar often look for all the world like cacti (which are only present in the Americas), but are from a completely different family. These disparate species have come upon similar means of water storage (water-holding stems) and self defense (spines) that allow them to exist in some of the harshest habitats on earth.

Epiphytes

The epiphytes include many of our favourite plants, and many species which people are used to seeing in pots actually spend their entire lives without ever sinking their roots in soil. Orchids and Tillandsia bromeliads (the now very popular ‘air plants’) are some of the more commonly recognized ones, but the vast majority of tropical plant species are in fact epiphytic. Some of the more common epiphytes available are lipstick vines and goldfish plants (Aeschynanthus spp. and Columnea spp., respectively), begonias, many aroids such as Anthurium and Philodendron, and many ferns. Using exclusively epiphytes together allows us to see the richness of these plant communities living far from the forest floor.

The planting pictured here is a good example of how we are able to execute the types of themes we explore, and also of how we, too, learn something new about plants nearly every day. We really wanted to make use of a particular tree, Afrocarpus gracilior, (also known as the Weeping Podocarpus), as the texture of the foliage and its dense, shaggy habit makes a really dramatic statement. It is also unique in that it is a tropical conifer, distantly related to our familiar spruce and pine. This group of plants, the gymnosperms, does not produce flowers, though it does produce seed, and arose during the Carboniferous period of Earth`s history, some 300 million years ago. It is this latter fact that we decided to explore for this planting.

The Carboniferous is so named due to the fact that this is when the great forests that were destined to eventually be swallowed by the ocean and preserved in the familiar form of coal were at their peak. It would have been a different landscape than the one we are used to today, for flowering plants had not yet evolved, and more simple plants dominated the prehistoric flora. Among these were the simple vascular plants which reproduce via spore such as ferns, tree ferns, and allied families, and the first seed-producing plants, of which A. gracilior is one.

Another primitive plant which produces seed but no flowers is Zamia furfuracea, also known as the cardboard palm. This is a cycad, related to the more commonly seen Cycas revoluta or sago palm. This plant was definitely a candidate for this installation, and its coarse texture and olive colour contrasted perfectly with our Podocarpus.

We had to represent the family of ferns in this planting (being one of the dominant flora of the Carboniferous), and chose two that highlighted the extraordinary diversity of form seen in these plants. Asplenium nidus, the birdsnest fern, with its rosette form of bright green, undivided fronds, is an epiphytic fern that grows on trees in Australasia. Microsorum pustulatum, the kangaroo fern, takes another approach to its growth: it creeps along on a hairy rhizome, from which emerge deep green, incised fronds which are more classically ‘fern-like’ than A. nidus.

One final plant was used in this installation: Psilotum nudum, the whisk fern. This species was chosen more for its story than for its form, which is nevertheless an attractive bunch of semi-erect stems, from which are produced spherical synangia, which contain the spore the plant uses to reproduce. The species has no leaves, no roots, and only half a vascular system, and is very primitive indeed in its physiology, and was a must-have for this planting. What we discovered in our research, however, was that there is some evidence that suggests that P. nudum may actually be descended from more complex fern species, and that it may have reverted for some reason to this very simple form. Perhaps we will never know for sure, but P. nudum is definitely a great representative for other similar species which were prevalent during the Carboniferous.

These themes tend not to be immediately apparent to the casual observer, of course, unless the plants are unified by a physical characteristic, and so the obvious question is why bother? We are able (and would be more than happy) to produce educational signage for anyone who wishes to show off the subtleties of their interior landscape, but we feel that with this much intent in our work, there will be a mood created which is tangible, and which adds depth and value to our landscapes. We hope to draw the viewer into our world and experience plants on a new level, and to connect them with a world most urban residents would never encounter otherwise.

Selaginella uncinata. Image © 天問小窩; retrieved from Wikipedia

Elaphoglossum metallicum, another iridescent plant. Image © In Situ Plants

Iridescent plants are a welcome addition to the interior landscape: who wouldn’t want a shimmering blue plant in their presence? There are several species (most only marginally available in cultivation) that exhibit this exciting type of colouration; Selaginella uncinata is perhaps the most available, under the name peacock spike moss. It can sometimes be found at garden centres and the like, and is produced by Exotic Angel Plants, amongst others.

I recently read an interesting article in The Scientist magazine on natural iridescence which explained something fascinating: iridescence is not caused by a pigment or a dye, but a structural property of the leaf (or wing, or feather, or whatever). Textures of the tissue surface are covered in ridges, bumps and dimples that refract the light in a way that appears to us as a metallic sheen. This adaptation is thought to have arisen during the Cambrian Explosion, as creatures were developing the first primitive eyes able to sense light, dark and contrast.

In cultivation, plants known for iridescence such as S. uncinata can show more or less of this colouration under different cultural conditions: I find that the best conditions for S. uncinata are moist, shady and humid (my default conditions for the genus). In bright light, this plant will blush pinkish-red, which can create a spectacular effect coupled with the iridescent blue, though it is a fine line to achieve both and maintain both colours. Apparently the ratio of red to far-red light makes a large difference in the production of iridescence, at least in the related species Selaginella willdenowii., though that`s somewhat outside the realm of the casual grower to play around with.

But perhaps the most intriguing aspect of this whole thing is the why: what evolutionary benefit do plants gain from this colouration? A paper published in the Journal of the Royal Society suggests two possible advantages: the iridescence may act as a deterrent to herbivores, as the (seemingly) constantly changing shape would not allow herbivorous insects, for example, to develop a search image (a familiar shape which the insect recognizes as a food source: search images abound, in our own minds as well as those of insects). The other possible advantage is that the iridescence (which is primarily seen in shade-dwelling plants, as I mentioned earlier) can prevent damage from exposure to too much light, say from a newly created hole in the canopy overhead that permits direct sunlight to reach the forest floor.

Whatever the reason, these plants hold a special fascination, and they are beautiful to behold. With a little care, these can make incredible additions to anyone’s indoor garden (and outdoor garden, if you are fortunate to live in a place with mild enough winters to get away with it).

Unknown Phalaenopsis hybrid. Photo © Arad; retrieved from Wikipedia

Did your eye even register the photo to the left? You can be forgiven if so: a beautiful sight it might be, but the now ubiquitous Phalaenopsis has become such a commonplace sight in homes and commercial settings that it’s nearly impossible now to regard them as the spectacular plants they are.

Tissue culture, offshore production and improved shipping techniques seem to have contributed most to the availability of these plants at nearly any place that sells plants (and quite a few that don’t): the US imported an estimated 400 40-foot containers of Phalaenopsis in 2010, and that number has surely risen since then. The plants are then forced into flower in greenhouses and then make their way to the mass market a few short weeks later. (This hasty method of production, though certainly bringing production [and thus retail] costs down, can also produce plants which may not perform as well after they leave the greenhouse, but that is a whole other post for another day.)

But why has Phalaenopsis become the poster child for the entire orchid family? After all, there are more than 26,000 species of orchid worldwide (many of them, admittedly, not suitable for culture, such as this exceptional species). Phalaenopsis was already being grown as a cut flower, which made it a good candidate for the early research into commercial production, and it is a very easy plant to grow commercially, growing rapidly and flowering reliably under the right conditions.

I don’t really have anything against Phalaenopsis in particular: there are over 60 species in the genus (check out the photos here), to say nothing of the countless hybrids therefrom. I’m definitely glad that more people are trying these plants out and having success with them. But it just seems a shame that the full diversity of orchids isn’t well represented in the mass market. The whole charm of orchids, after all, is their exoticness, and it certainly gets a lot more exotic than Phalaenopsis. Even other commercially produced genera offer a little more curiosity, and these are often easier of care for the novice than Phalaenopsis, and can also have more unique foliage so that they hold visual interest when not in flower.

It doesn’t seem as though the humble Phalaenopsis is going anywhere any time soon. Perhaps the best we can hope for is that other species become equally well-represented in commercial production. And my personal hope is that many species become so well-represented: the Orchidaceae really are incredible, and everyone should have the opportunity to try growing something a little different.

The world of plants is one of staggering variety: to date there are around 400,000 species known to science, with many more waiting to be discovered. An interesting facet to this variety is the fact that there can be incredible diversity within species themselves, such that different individuals of the same species growing side by side might not be immediately recognizable as being at all related.

Oftentimes, a variety will supercede the parent species in popularity, perhaps because it performs better in cultivation or has a more interesting appearance, and becomes used more often than the ‘original’ species. (Note that I am not discussing man-made hybrids or cultivars here- that is a subject for another time.) A perfect example is Dracaena fragrans ‘Massangeana’, which sports a pale green stripe down the center of its leaves not present in the typical D. fragrans. One doesn’t even really see the boring old D. fragrans anymore, so popular has its variegated variety become.

But would the effect of ‘Massangeana’ not be greater if it were a single specimen amongst several of the regular D. fragrans? After all, that’s how one would find such a variety in nature: they would stand out like a sore thumb, and perhaps even give taxonomists a run around thinking it might be a different species. I think it would, and so that’s what I do with these types of plants.

I believe that, rather than leaving these varieties to stand alone as representatives of their species, they should be incorporated and used (sparingly) with their parent species to highlight and exemplify the fact of their origins, and to allow people a glimpse at the near endless variety of the plant kingdom.

Tag: vertical garden

Why You Can’t Live Without Plants

The Myths of Phosphorus and its Overuse in Indoor Horticulture

Ferns from Scratch, Part Two

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

Watering 102: A Guide to Watering Interior Plants, Part Two

Watering 102: A Guide to Watering Interior Plants, Part One

Thematism in the Interior Landscape

Plants that Shine: Iridescence in the Indoor Garden

Why I Hate Orchids

On Natural Variation and its Place in Interior Landscaping