What’s at the root of happy houseplants?
Consider the carrot. Whether you like vegetables or not, I’m willing to bet that when you think ‘carrot,’ you imagine the edible, orange part and not the leafy, above-ground part. Which is another way of saying that, in this particular instance, the root is cool and the plant is boring. And what a sweet, colourful, crunchy root it is.
Now consider the houseplant. Yes, you guessed it: now the plant is suddenly cool and the roots are boring.
For houseplant lovers, roots are like the internal organs of a romantic partner: vital but nothing to dwell on. No matter how huge of a plant collector we might be, most of us are perfectly happy never to see the roots. Like a black pot instead of a black box. Sure, when propagating or repotting, we might be momentarily curious about them, but for the most part it’s out of sight, out of mind.
So what comes first, the chicken or the egg? Which is to say, putting your biases aside for the moment, does the carrot exist for the foliage or does the foliage exist to make the carrot? Do the roots make the plant or does the plant make the roots? If you say it has to be both — above ground for photosynthesis, and underground for nutrients and water — then we’re getting somewhere; your focus has already widened.
Roots are as much of what we’re growing when we grow houseplants as is the ‘plant’ itself — whether we like it or not. Anyone who loves foliage is forever root bound.
The first step in getting more interested in roots is to acknowledge their existence inside the pot. The mention of pot here is important because, as you know, plants didn’t evolve to reside in pots. It’s not just limiting, it’s artificial. Which places even more importance on thinking about the roots, since the way we grow houseplants asks a lot of them.
Endless posts are made online every day concerning houseplants, with up-close images of sad looking plants, asking what’s gone wrong. Look at that drooping foliage! Those yellowing leaves. The decimation caused by spider mite. Unfortunately, rarely do such posts offer any images taken of the roots. That’s the big difference between indoor plant enthusiasts and outdoor gardeners. Nobody wants to get dirty!
The problem with ignoring the roots is that foliage tends to show only symptoms, while what’s in the pot can tell us about underlying causes, like ersatz soil or root rot. Just today I was asked to sort out a 40-year-old Cast-iron plant that had been handed down a generation. The owner was in a panic over yellow, new growth and brown tips. It had been ‘encased’ in a fibre pot so we cracked open the egg and looked inside. The roots were generally abundant and most looked good (firm and healthy white), so you could see the problem straight away. I told the owner the roots were getting some water but not enough to share with the foliage — ‘you’re not watering this very much are you?’, I asked. And she said, maybe once a month.
The word ‘radical’ comes from the Latin radicalis, which means root, so a radical approach to plant care means getting to the root of it. This is especially true for houseplants because so many issues have to do with either watering or a resistance to changing out the soil, both of which directly impact root health.
So don’t be shy, lay out some newspaper, whack that pot off, and have a look at what’s going on in there. The great thing about most houseplants, including tropical ones, is that they don’t mind occasionally having their roots (gently) disturbed. Once you get the habit of looking inside, you won’t regret it. There’s a whole world in there and learning what healthy roots looks like will help you sleep at night.
Even if the news is bad, it’s far better to act sooner than later. The image below shows what happens if you don’t. Last autumn I received a few dozen of these anthuriums from a nursery that had given up on them. They were medium size and about four years old. Clearly, they didn’t know how to grow them, and neither did I. How could they be so small after four years?
I looked online and saw first of all that the nursery had mis-identified the plant. Next I realised that my newly bought friends were nowhere the size of the nice green ones I saw online. So something was holding them back. I couldn’t find any useful technical info, so I removed the pots and looked at the soil. All seemed fine. Hmm…. The roots were firm and plentiful, so I tried to get them going by making the soil even more free-draining and thus oxygen friendly. Then I put them in a warm shade house.
But it was winter and, behold, they suffered from my one-size-fits-all approach to watering. Realising this I took the pots off (again) and inspected the mush I had created (compare to the amazing roots in the next photos above). Some have been saved since and are doing well in a new epiphytic ‘soil’ (a tree-fern substrate), while others were lost. So do as I say, not as I do, and keep your eye on those roots.
Taken by (the) Roots
Some people get pretty excited about roots…
Let’s talk about roots. Some may find this a little strange but I find growing roots just as satisfying if not more so than growing foliage. I know they’re not as big or as shiny as a philodendron leaf nor are they as colourful as a begonia, (actually they can be…) but without a fine set of roots you won’t have much of a plant to admire anyway. I love them so much that I grow almost all of my plants in clear pots just so that I can see them. source
Another step toward becoming more like this root enthusiast is, I think, getting to know roots better.
Aroids like philodendrons and some anthuriums and ferns are an interesting place to start, as they have both roots above the soil as well as below. Plenty of roots to go around, you might say. As we know from our Ficus trees, Pothos (Scindapsus) or Monstera Deliciosa, aerial roots can grow from the stem of some plants and some these of remain above ground.
Houseplants like Crotons or Calatheas, by comparison, do not have such roots and are terrestrial by nature (i.e., they have the ‘traditional’ root system growing from the base into the soil). Although this is what we usually think of when we consider houseplants, even here there are special aspects to consider. Consider the question of repotting:
Most repotting of plants involves removing the pot and replacing it with a larger, new pot, with some new extra soil. But should it?
This is not always the best technique. Remember, you’re working with a potted plant here, which only needs limited soil — you’re not trying to simulate the planet Earth. If a plant is proportionally too large for the pot (top heavy) a repot might be okay. But if the plant is not top heavy, you may be able to just put this plant right back in the original pot — after working on it. This should not come as a surprise, given that nurseries almost always sell plants in pots too big. Repotting back into the same container is something we learn from bonsai. Imagine if an 80-year-old bonsai tree was repotted into a larger pot each time it needed its soil renewed. That would be an awfully large pot.
Meanwhile, if a larger pot is in order, that’s no excuse for just chucking it in a new pot as it, with some new soil added along the perimeter.
Better to dig in. Do you really want to keep all that old soil forever that’s inside the rootball — the most vital part of the root system? Most of us fear bare-rooting a plant, thinking we might kill it. But it has to be done. Totally hydrate the soil overnight, then remove the pot, then free the soil from the roots as best you can. Use a fork. Go hard, the more old useless soil removed the better. Cut off excess roots at the bottom. Just make sure you do this during warm weather. Don’t water the new soil too much if it’s moist. Pack the soil down deep… further, further. Now watch it grow.
Roots that begin their life above the soil, are deemed adventitious. Depending on the level of humidity, these root can take water from the air and can even photosynthesise — thus having their cake and eating it too. Orchids do this even when potted in orchid mix, if in a clear plastic pot. Although the orchid’s aerial roots are seemingly below ground, the pot is actually simulating a humid, epiphytic environment in which the roots drink and breath from the air, and maybe process some light.
The aerial roots of aroids are prepared for an uncertain future, not knowing what environment lies ahead. For this reason they retain a built-in plasticity, meaning they can change depending on where they find themselves. For instance, if you damage or remove the terrestrial root system, the remaining aerial roots will accelerate growth and branching. Individual aerial roots also retain an ‘epigenetic’ ability to adapt in both form and function.
Often people ask about all the crazy roots coming off the trunks of their Monstera Deliciosa. Some of the these aerial roots are close enough to the base that they make it into the pot’s soil and become terrestrial. At this point they undergo changes in form and physiology.
Above ground these roots will be suited to photosynthesis and taking in moisture from the air. But as the scientific study pictured above describes, upon reaching the soil — if and when — the roots change. They go from brown to white, slow down in growth, and begin producing root hairs. Soon lateral roots form from them in the soil with the result of dramatically increasing the volume of roots in contact with the soil. This helps anchor the plant while also increasing water and nutrient uptake and transport.
Better When Wet
When is the time we most often think of roots? I think the answer is when we’re watering. We wonder about what’s going on in there: are all the roots moist?; too moist?; are they happy?; too crowded? As is often pointed out, poor plant performance almost always involves the health of the roots, which might be damaged by dryness or overwatering (sometimes you need to soak the plant if it’s become too dry, much like a dry sponge; other times we’ve been loving our plants to death with too much water). Whatever the case, when we think of roots and soil we usually think uni-directionally: soil → roots → trunk/stems/branches → foliage.
This though is simplistic. You won’t be surprised to find that plants are too old (evolutionarily) and too smart to be so simple. Yes, roots absorb water and nutrients from the soil to transport them above ground to the trunk/stem and beyond. But plants and their roots can also use their internal moisture to actually hydrate the dry roots and even soil. We know this first from the example of succulents and other, water-retention plants (xerophytes), including cacti. The roots of these plants can survive zero-moisture conditions only because they hydrate the roots reverse (spread the love).
A related problem occurs when some areas of the soil mass have been too dry to absorb moisture (i.e., become hydrophobic). The result is that some roots are being watered but others are not. At least for a time this can be overcome in some plants by a similar process of moisture exchange.
For plants in the ground, a similar and interesting process is called hydraulic lift. In some natively dry conditions the moisture levels in the upper areas of the soil will become so dry that the roots closest to the base would be damaged despite the fact that there’s moisture further down. In such cases, moisture absorbed by roots deeper down is actually carried upwards at night and released via the shallow roots into the soil. Then, the following day, that same moisture in the soil is taken up and carried to the plant via the shallower roots (source).
Even more impressive is the possibility that via the same process, nutrients are moved from lower soils up to the shallow roots and the surface soil. ‘What we're discovering is, through a process called hydraulic lift, plants also leak water into the bone-dry surface soil to release nutrients and stir microbial activity critical to the plants’ survival,’ writes one researcher.1
We’ve seen that roots live a varied life and are less static and boring than we thought, both above and below ground. Tropical plants with aerial roots are a bit like people: they have feet on the ground but also have arms to hold and feed themselves. From this point of view, epiphytic plants have a greater capacity than terrestrial ones to adapt to their environments, or take them over. They can climb up and they can climb down; they can live in a tree, or in the ground; or up a pole, or in a pot. This is why jungles exist, and why we think ‘jungle’ when we see a dense houseplant collection. Sometimes adventitious roots can be a little too adventitious.
By the way, here a list from online of some houseplants that don’t mind being root bound: hoyas, peace lilies, spider plants, aloes, ZZ plants, asparagus ferns, snake plants.
John Stark — professor at Utah State University's Department of Biology and Ecology Center