Soil...dirt...compost...humus...potting medium--any way you say it, the stuff plants grow in doesn't really sound exciting (well, to most folks, at least!) The truth is, soil may be the most underrated and overlooked thing we see every day.
Unless you're a farmer, I'll wager that not many of your conversations center around soil, yet, it's so essential that life as we know it would cease to exist without it! Plants, yes, but also every fungus, every animal, every bacterium or virus on earth is fundamentally dependent on the health of soil.
And when it comes to growing tropical plants (or any plants, really), soil is the first and most important consideration. To get an idea of what our plants need, it's helpful to consider their origins. Most tropicals, which includes the majority of houseplants, are, well...tropical!
That is, they stem from the regions of the world nearest the equator, where there are two primary seasons: wet and dry. Or we might better say, "wet and wetter!" Abundant rainfall is one of the hallmarks the tropics and subtropics. And in a very moist, humid environment, plant life tends to fall into three broad categories:
Canopy Plants
These are the trees and other tall plants (for example, Bananas, which are technically not trees because they don't have woody stems and produce bark, but are simply very large herbaceous plants) that provide the "roof" for the tropical forest. Their roots are in soil that is shaded by their own leaves, and their reproductive strategy is to stand tall, raising their limbs far above most other plants, and bearing fruit that attracts aerial and arboreal feeders like birds, bats, monkeys, and other talented climbers. Sadly, few of these are good candidates for home growing, unless you have a verrrrry large windowsill! Brazil Nut trees, for instance, can reach a soaring height of 160 feet (the height of a 16-story apartment building), with trunks two grown humans could barely reach around!
Understory Plants
Understory plants are the "workhorses" of the tropical forest's botanical community, busily filling-in every patch of dappled sunlight afforded by breaks in the canopy and working with insects and fungi to break down dead organic matter into fertile soil. Their roots also anchor this same soil, preventing runoff when torrential rains come. When we think Understory Plants, we think of the denizens of the forest floor, growing in the shade of Canopy Plants and benefitting from the compost formed by their falling leaves, as well as the host of creatures that climb there and occasional drop their "calling cards" on the forest floor. These plants enjoy a rich, organic soil that stays evenly moist. As houseplants, they resent drying out for any significant period, and they want a rich medium full of things like peat and compost that offer a wide spectrum of nutrients for their roots to absorb. At the same time, the forest floor is often fairly porous, and plants that grow there like to have moisture drain away quickly, so that their roots aren't "swimming." Remember, plants have to breathe, too, and though it's carbon dioxide they chiefly need, if their roots are waterlogged, they can literally suffocate. In terms of lighting, many Understory Plants are fine with what we at Specialty Tropicals always call "bright shade." Though it may sound at first like an oxymoron, what we mean is, not inky darkness, but never direct sun. Of course, in each of these regions of the forest, there are a numerous microclimates, each with its own flora suited to grow there, so some species may tolerate appreciably more sunlight or water than others.
Epiphytes
Many novice horticulturists are surprised to discover that a huge chunk of the tropical plants we love are naturally epipyhytic--that is, they don't grow in soil at all, but attached to the trunks of trees and other plants, on rocks, or simply hanging among the branches overhead (think Spanish Moss!) It's helpful to understand that the vast majority of Orchids, all Nepenthes (tropical Pitcher Plants), many Aroids (Philodendrons, Anthuriums, and their kin), Bromeliads, Hoyas, many Ferns, and even some Cacti naturally grow as epiphytes. Knowing this helps greatly inform our choices of growing media for those plants. It would be a misnomer to say that these plants can't tolerate any organic soil, because in truth, most of them accumulate some humus or composting leaves, etc. around their roots, even hanging on a rock cliff or bound to a tree trunk. The major exception would be the tropical Carnivorous Plants, like Nepenthes, which are very intolerant of fertilizer or other soil enrichments. If Understory Plants need good drainage, it's obvious that Ephiphytes really do, so we craft planting media for them that are full of things like fir bark, perlite (a lightweight volcanic mineral that's literally "popped" like popcorn), clay pebbles (leca), and Sphagnum moss. All of these ingredients allow for significant airflow around the plants' roots, while also providing a stable substrate. Sphagnum holds moisture well but becomes waterlogged (the stuff is really like a sponge, absorbing hundreds of times its own weight in water), so we temper its moisture-holding properties with lots of perlite or other stable, non-absorbent materials that provide air pockets around the plants' roots. And because epiphytes range from the understory to the canopy and everywhere in-between, there are many species-specific considerations for their potting and care. Many orchids, for instance, like to live in slotted wooden baskets. In the case of Vandas, they need little or nothing inside the basket--just a container to suppor them, with their roots bathed completely in air. The same is true of many bromeliads like Tillandsias, while other Broms prefer a well-draining soil mixture to cling to. Nepenthes are particularly fond of air circulation in the root zone and intolerant of soggy soil, so we pot them in a 50/50 mix of Sphagnum and perlite, which nicely marries water retention with aeration. So, what overall conclusions can we draw about potting tropicals? Well, for one thing, there's an important balance to maintain, between consistent moisture availability and the need for air circulation in the root zone. Whether the medium is soil, moss, bark, or air, almost all tropicals will benefit from good drainage and an open, loose substrate. Except in the case of the carnivorous Nepenthes, which traps insects and small animals to provide its nutritional needs, most tropicals appreciate generous feeding year-round and a fertile soil full of organic components.
Have questions about how to pot and grow your tropicals? Please refer to our "CARE" section on the website or contact us for a personal consultation. We're always happy to help, and we love talking with fellow plant-nerds!
Happy Growing from the crew at Specialty Tropicals!
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