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.
Xeric (dry) habitats
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.
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.