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This is one of those planty subjects that’s more or less up to your own discretion.
Everyone has their own way of doing things, and by and large, it doesn’t really matter what you do, as long as your plant is ok in the end.
It’s also something that people are SUPER opinionated on.
I don't break up the root ball (unless necessary) mainly because I think it's unnecessary, but there are people out there that are of the impression that if you so much as look at the roots the wrong way, they'll wither and die and you'll have to reroot it.
The roots of a healthy plant are more resilient than you might think
The roots of an unhealthy plant are NOT resilient, but you won't need to break them up, so it doesn't really matter
Please note that house plant and outdoor plants are a bit different in terms of root strength.
Outdoor plants have a more natural existence – there’s more light, and the added stress caused by e.g. wind makes them more chill than indoor plants. They become more adaptable.
Just because you can rip the roots apart on your Hydraganea (which you can, I have and it thrived) doesn’t mean your Syngonium will appreciate the same treatment.
Should you break up the roots when repotting house plants?
If it’s just a usual repot (i.e. it’s not horrifically rootbound) I wouldn’t bother.
Not because doing so will harm the plant – it probably won’t care. Just because it’s unnecessary and you could potentially harm the roots by accident.
The roots will spread out naturally into the pot over time. Even if they don’t, the roots around the edge will come into contact with more soil, so will be able to absorb more moisture and nutrients.
If you want to tease out the roots a bit, for example because they've started spiralling around the bottom, you definitely can, but you don't have to.
It really doesn’t matter. The plant will sort itself out over time.
In shallow-rooted plants such as hoya, you may find that the roots never spread out. Well, they maybe are a bit, but Hoya aren’t known for their speedy growth.
I have a Hoya Krimson princess that’s root system kept the shape of its previous pot for a couple of years, and continued to grow happily.
How to break up the roots of a rootbound plant
Sometimes it’s necessary to break up the roots, just because they’re so entangled it affects their ability to absorb nutrients from the soil.
Even so, you don’t actually need to break the roots up if you’re worrying about damaging it.
Thoroughly soak the root ball to hydrate it – leave it for about an hour so you know it permeated the inner roots.
Then let it dry for a couple of hours, and put it in a new pot. Fill around the edge with moist soil. The roots will grow towards the wet soil naturally.
I don’t recommend soaking the rootball unless the plant is super rootbound, because if the plant is thirsty it’ll send out new roots into the new, damp soil faster.
However, with severely rootbound plants, you don’t know how long it’s been since the inner roots were properly hydrated. Taking the chance to thoroughly soak it could prevent problems down the line.
If you do want to break up the roots, there are a few ways to go about it.
I would always start by soaking the root ball. Roots have a large surface area and stick to each like glue.
Softening them with water can loosen them up BUT there may well be sections of roots that are compressed together.
If they don’t come apart easily let them be or risk snapping them. Snapping them is fine, I just want to prepare you for the fact that they probs won’t all come apart.
Some people choose to sit down and manually untangle the roots. I am one of them (when the mood hits). I also like braiding hair, so I assume these things are linked.
It is, however, largely unnecessary.
If you want to spread them out but are impatient, then grab a knife (yup, we’re doing it!) and use the tip to make a few holes in the base of the root ball.
Use the same movement that you use for breaking up stuck ice cubes – knife in a crevice, wiggle it around in a gap between two roots and hope they pop apart.
The reason I advise sticking a knife in the bottom is that you’re less likely to take out a really important root that’s connecting a million other roots to the plant.
How to encourage houseplant roots to spread out
As the plant gets over the sheer shock of being repotted (and possibly attacked with a knife), the roots will begin to spread out naturally.
Whilst I obvs don’t want you to overwater, make sure you don’t let the soil dry out too much at this time, because you want the roots to grow.
If anyone has any tips for just watering the outer edges of the pot to encourage the roots to grow into the new soil I’d love to hear them.
Bottom watering can also encourage the roots to grow down BUT you do have the added annoyance of roots popping out of the bottom and making the pot tilt. It doesn’t bother me, but I know it bugs some people when their plants won’t stand up straight.
What happens if you break the roots when repotting?
Provided you don’t break like, every single one, likely not a lot.
As I’ve already said, plants are adaptable.
Roots break, they’ll get over it.
Many plants will even have a little root growth spurt after a significant loss.
The issue with this is that it'll seem like your plant is taking ages to recover after repotting. It's more than likely fine, it's just concentrating on root growth, not leaf growth. It is frustrating though, and depending on the plant can mean they don't produce new leaves for several months.
If they have to grow new roots to replace the old roots and then also grow roots to fill the pot (Monstera like to be cosy) it could be a literal year until you get new growth.
I’d love to hear if anyone has any opposing views on this, but in my experience, there’s no benefit to breaking up the roots when you repot house plants.
It’s different with crops. Breaking up the roots can force faster growth, or more compact growth or whatever that plant’s deal is.
That’s not really an issue with houseplants. We just want new growth asap, which is why I try not to disturb the roots. I try to minimise disruption as much as I can so they barely notice, and I don’t have to deal with a leaf-dropping tantrum.