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Does it ever feel like an important piece of knowledge or information just completely passed you by, and then one day everyone starts talking about it and you’re like ‘wait…you all KNEW? And no one told me??’
That’s kind of how I found out about letting cuttings callus over. I knew that you were meant to let succulent cuttings callous, but that just made sense – succulents hate any part of them being wet, so I assumed it was succulent-specific and carried on about my day.
But then I discovered other people had ‘leave cutting to callus for 24 hours’ in their propagation instructions. It was something people either instructed you to do or completely failed to mention.
So is it important? Does it do anything? Or can we skip it if leaving something for 24 hours condemns it to be forgotten about for at least a week*?
*I can only think about one thing at once, so by the time my cutting has callused, I’ve moved onto something else.
What does it mean to let a cutting callus?
Letting a cutting callus is just leaving it to heal in the open air for a bit.
When we take a cutting from a plant, it creates a wound (like when we cut ourselves). The best way to let that wound heal is to leave it exposed to oxygen.
(This bit deviates from humans, because if you chop off one of our limbs, leaving it to callus over isn’t really gonna cut it)
The wound will dry up and scab over a bit.
How long should I let my cutting callus?
There’s no right answer here. I’ve seen people recommending 72 hours, and others saying that an hour is perfectly sufficient. And then there are heathens like me that didn’t even know it was a thing until 2020, and still don’t really do it now.
It really depends on the plant.
And don’t worry, about leaving it too long (like…within reason) – cuttings can last without water for longer than you might think.
Which plants need to callus when propagating?
It’s really difficult to sort out the science from the ‘we’ve always done it this way’ BUT also…many professional succulent growers say it works, and they would know.
The general consensus with succulents is that letting them callus before propagating can dramatically reduce the chance of them rotting.
Not too many people recommend letting aroids callus over (not because you shouldn’t but because it’s not 100% necessary), but most succulent growers do.
The amount of time suggested to let them callus over varies from between one and three days, and is an intrinsic part of the process. The callusing process seems to kickstart the leaf propagating, according to many growers (though biologists disagree) which seems like a good reason to do something as painless as letting a leaf callus over.
Many succulents propagate differently to aroids, especially succulent leaf cuttings. The leaf roots, and then provides nutrition for a new plantlet to grow, rather than just continuing to grow as an aroid cutting would.
These leaves are usually laid on soil, which can make them more prone to rotting than an upright stem, so letting them callus over is an easy way to reduce the chance of them rotting.
From my experience, you can successfully propagate stem cuttings without having to let the end callus, as long as you don’t overwater and get good aeration to the roots.
I tend to prop my jade plant in summer, which is probably why I've never had an issue with rotting despite not letting the ends callus over - the warmth, light, and windy weather allow the soil to dry out quickly, but then since its the UK it usually rains soon after.
You definitely don’t need to let Pothos callus over in order for them to propagate. I very rarely do, except for by accident when I wander off in the middle of taking cuttings and then remember an hour or two later.
However, if you struggle with your cuttings rotting, then you might want to try letting your cuttings callus over for a couple of hours (or overnight) before putting them in water.
I’ve tried both ways, and it made no discernable difference to the speed at which the cuttings rooted, but it’s worth a try if you’re not having much success.
I’ve written an article here on how to stop your cuttings from rotting.
Basically the same as Pothos – do it if you want to. I’ve never let a Monstera cutting callus over before propagating it, and I’ve never had one fail.
Whilst letting a cutting callus won’t harm it, it won’t do anything magical either. There are other things you could do that would dramatically increase your chance of success, so try increasing the temperature and humidity if your Monstera cutting is stubborn.
Should I add rooting hormone before or after callusing?
Rooting hormone is a pain. It needs to be applied to something damp so it’ll adhere, but if it gets too wet, it’ll shift and drop off. If it’s applied to a dry cutting, it’ll just fall off.
It’s entirely up to you. I would probably apply a little bit first, then dampen the end after callusing and apply a bit more. That way all bases are covered.
I see a lot of people applying rooting hormone and then putting their cuttings in water, but I was led to believe that it doesn’t work in water because it needs direct contact with the stem. If anyone has any insight on that, I’m all ears.
There is quite a lot of talk about using cinnamon as a rotting hormone, and, er, it’s not one. Some people have had a bit of success using it as a fungicide, but it’s usually using true cinnamon, which is more expensive than cooking cinnamon. It’s either called Ceylon cinnamon or Cinnamomum zeylanicum.
What happens if I don’t let a cutting callus?
We let succulents callus over because the leaves hold water and it can cause rot. So therefore it seems clear that if you don’t let succulent cuttings callus they’ll rot.
This actually isn’t strictly true – it will depend on a tonne of factors, mainly your environment (if you live somewhere hot there’s less chance of rot) but also the type of plant, health of the mother plant etc etc.
So callusing reduces the chance of succulent props rotting, but doesn’t prevent it entirely AND uncallused props still have a perfectly decent chance of not rotting. It’s a precaution, not a prerequisite. It may speed up the process (no one’s entirely sure – hobbyists say yes, botanists say no) but it’s not 100% necessary.
There isn’t much information on this, but one of the main reasons people give for letting cuttings callus over is to prevent diseases and bacteria from entering the wound.
This thread on Reddit (I know it’s hardly the best source, but also it’s all we’ve got) has a comment from a botanist saying that this isn’t true, and I believe him.
For a start consider when we have a wound – a scab forms to prevent further blood loss, which is why I assume plants callus – to prevent moisture loss.
Scabs do reduce the chance of infection, but it isn’t the scab itself – it’s the inflammation that comes after the scab has formed.
Apologies for all the scab talk, but I like analogies.
I don’t know if plants have similar mechanisms (they probably do) but even if you don’t allow a cutting to callus over it will still do what it can to reduce the risk of infection.
I know there really aren’t any definitive answers out here, but that’s because there aren’t. I had a quick scour of the r/succulents subreddit and a LOT of people don’t even let their succulents callus.