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Aerial roots are adventitious roots (i.e. a root that’s growing somewhere other than underground) that many climbing aroids produce to help them attach to the tree that they’re climbing up.
They’re not really necessary for houseplants.
Sure, it’s easier if they attach to moss poles themselves, but often that’s more work than it’s worth (I have enough plants to water, I don’t need to be watering moss poles too).
If your aerial roots aren’t growing, it’s rarely a reason to panic about your plant’s health (unless there are other symptoms too).
But what if you want your plant to climb by itself and it’s refusing to grow aerial roots? Or, it’s growing them, but they shrivel up into brown stubby nubs.
Well, there are a few things you can do.
They’re not needed
Aerial roots require effort to grow, and when they’re not needed they often just shrivel up.
This is hugely dependent on the plant. For example, Monstera often grow aerial roots for absolutely no reason. Look at this one:
They have a brown bark-like covering that you can snap, and underneath it’s green and more flexible, so I’m working on directing it back into the soil to give support. Notice my Hoya parasitica black edge climbing up it at the base.
Sorry for the blurry photos, but my iPhone camera can only focus on one thing at once, and it literally couldn’t see the aerial root when I tried to focus on that.
Other plants won’t develop aerial roots unless they’re either climbing up something they want to attach to OR the humidity is so high they’re like ‘well, why not?’.
If your humidity is low and you have no interest in increasing it, you’ll need a moss pole that the plant wants to root into.
A coir pole won't do - you'll either need a proper moss one that you can keep moist OR get a kratiste one that your plant will grow into.
I LOVE my Kratiste pole. Look at this Syngonium clinging on:
Some plants also seek out walls to climb up – the only two that seem to actively prefer walls to anything else (in my experience, anyway) are Monstera deliciosa and Rhaphidophora decursiva. No idea why!
My Rhaphidophora decursiva got so far off the wall and then dropped off, so she’s had to onto a Kratiste pole.
The other option is just a buttload of humidity. In the terrarium, every aroid I have is lousy with creepy, furry aerial roots.
Whilst most plants will grow strong aerial roots in either of these scenarios, some are more predisposed to grow them than others.
Philodendron brasil, for example, seem more inclined to grow aerial roots than regular heartleaf Philodendrons.
It probably has more to do with the genetics of the parent plant (since most of these plants will come from tissue culture) than an evolutionary thing.
Aerial roots can get damaged easily because they can be quite brittle when they’re not attached to something.
I have snapped them in the past, and they can continue to regrow if they’re still attached a bit (sometimes – it depends on the conditions) rather than completely severed.
They will also stop and start growing – either continuing to get longer or branching off.
It’s not so much that low humidity stops aerial roots from growing, as it is that high humidity really kicks them into gear.
If you want aerial roots to grow but you don't want the plant climbing up something, then you need to either get a humidifier and crank it up to 80% or put your plant in a clear plastic box with some damp moss and create a little terrarium for it.
Once you lower the humidity, they’ll usually stop growing. They may also detach from whatever they grew up.
Low light doesn’t specifically stop aerial roots from flourishing – it puts a stop to all growth other than leaves because the plant needs more leaves to photosynthesise when it’s kept somewhere with suboptimal light.
Growing your plant up a moss will help a bit, but you really need to either move the plant somewhere brighter or get a grow light.
Incongruent is such a good word. It basically means you go through phases of neglect and it can affect your plant’s growth.
In my experience, just taking care of your plant well will result in aerial roots that grow quickly and don't just shrivel up BUT you also still need to provide a lot of them with a purpose - i.e. something to climb up.
Like low light, pests tend to just stop growth full stop, and your plant may stop sending nutrients and water to any aerial roots because it needs to concentrate its energy on protecting itself from the pests.
Lack of fertiliser/too much fertiliser
I tried an experiment this summer that involved fertilising my plants every time I watered. I discovered that for the first couple of months, everything went wild – leaves, aerial roots, everything.
However, after a bit growth slowed down. I think they all got overexcited and overexerted themselves.
I switched to fertilising every other time I watered (and less often for a couple of plants, which need their own article) and that seems to be working really well.
I have noticed that my Monstera and Hoya are growing faster, and with fast growth comes aerial roots and tendrils.
Genetics of the plant
I’ve already touched on this – I noticed that some heartleaf Philodendrons refuse to grow aerial roots unless they’re in super high humidity, but others, specifically Philodendron brasil, seem predisposed to grow them as a matter of course, despite conditions.
In both cases they will shrivel in time if they don't find something to attach to BUT P. Brasil ones grow more aerial roots and they grow longer before they dry up.
My Cebu Blue is trailing, so its aerial roots aren’t needed. Therefore, they look like this:
However, there are other aroids that can produce aerial roots, they just have to have very specific conditions and others that can grow aerial roots but they don’t like to actually use them, and you’ll have to attach it to the pole yourself.
The main offenders here are hybrid Philodendrons, specifically ones that have parents that are self-heading.
It makes sense - self-heading Philodendrons don't need aerial roots, so their offspring might not have the right genes to grow good ones.
There are loads of plants in this category, but the ones see cropping up often being shamed for their lack of interest in growing aerial roots (or growing them but refusing to attach to a perfectly suitable moss pole) are Pink Princess, White Princess, White Knight, and White Wizard.
Can aerial roots start growing again?
Yes, absolutely. Even the most shrivelled brown nub can be revived and start growing, apparently apropos of nothing.
If you feel like your humidity is plenty high, you have a moss pole, and your care is good but still nothing, you can try air layering your aerial root to convince it to grow. Sometimes they just need a little nudge in the right direction.
You need to convince your plant that it needs aerial roots if you want it to grow them. Give it high humidity, and a moss pole it can attach to* and you should see results without doing much else.
*Coir poles rarely work here, but the Kratiste ones are a great option if you cba to keep sphagnum damp.