Q: I’ve become interested in air plants and would like advice on how to grow them. I hear conflicting feedback on how easy they are to keep.
A: I’ve been growing these for years and find them easy, but keys to their success indoors are bright light, good air circulation, and recognizing when they need water. (Ok, yes, that last tip is applicable to every plant, but it’s extra-critical here.)
A member of the bromeliad family, air plants (tillandsia) are named for their ability to subsist on moisture and nutrients aloft in the air, as opposed to root absorption. Often clinging to trees or rocks in the wild, their roots just keep them attached — they don’t parasitize a host tree and can grow perfectly well without roots if needed. (Picture the curtains of Spanish moss in oaks of our southeastern states — those are also air plants.) Keep in mind that this ability helps them survive in nature; our home interiors are a very different environment where they can’t be as self-sufficient.
Structures called trichomes on the leaf surface are specialized in air plants to absorb moisture, somewhat like a wick. A pronounced trichome layer is what gives most species their felted coating which makes them look silvery or fuzzy. When dry, the trichomes act like shields to reflect some of the intense light common to air plant habitats. Kept too wet, these trichomes get matted onto the leaf surface for so long that it deprives the leaf pores of gas exchange — in essence, they suffocate.
Indoor air is fairly dry and doesn’t allow air plants to absorb enough airborne moisture; over time, they lose more than they can replenish. Other bromeliads use their leaf bases as water reservoirs, but tillandsia are not adapted to do this and can disintegrate if kept damp. Misting the foliage may delay the inevitable, but it doesn’t fully quench their thirst. Instead, now and then they need a good drenching.
I don’t have a rainy summer’s day handy, so I soak mine in a tub for several hours once or twice a month and then shake the excess water off. Watering frequency varies from person to person because your growing conditions will be unique.
Of vital importance after soaking is that the crown – where the leaves attach to the body of the plant – dries off quickly enough, ideally within a few hours. Avoid displaying your plants in glass globes or terrariums as they reduce airflow. A small fan can help to circulate air around.
Given the rot risk and the misconception that they’re self-sustaining indoors, it’s understandable that under-watering is the other common cause of air plant loss. How can you tell when to drench? Look at the leaf shape. For many species, the long edges of the leaf will curve upward when the plant is getting dry, much like your tongue’s shape if you roll the sides up. After a soak, see how the leaf shape has flattened and use this as your baseline to compare to in the future. Different species have different degrees of natural curl to the leaf, but a well-hydrated plant will show you what’s normal for its type. For species that naturally have more of a noodle-like, cylindrical leaf, you’ll get used to how their leaves might twist and twirl more when drier, and a drying plant will feel lighter.
Lacking a sunroom, I grow my air plants under bright artificial light, and have had several species bloom and produce offsets (pups) regularly. Remember that those silvery trichomes are acting like a sunscreen, so you need to compensate by giving plants bright light so enough energy makes it through to the chlorophyll. Tillandsia species with greener leaves will be fine in moderate light because their trichomes are sparser or smaller. None can subsist on low light long-term.
I admit I often forget to fertilize, but periodic nourishment added to your watering regimen will help boost growth. That said, air plants are generally slow growers because they evolved to make do with limited resources in harsh conditions. Their nutrient needs are therefore quite modest, so if in doubt, give them a more dilute fertilizer solution than the label advises. Orchid- or tillandsia-specific formulations are best because they don’t include urea, a form of nitrogen that plants not growing in soil can’t utilize by itself.
The good news is that, even with a moderate level of care, air plants can be very long-lived: as with other bromeliads, many reproduce eagerly and will develop into an impressive clump over time. Or, you can separate them when they’re large enough and trade them with friends.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.