Is my plant pot-bound, and what do I do about it?
The three stages of root congestion, the signs that identify each, and why circling roots have to be cut rather than teased apart.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 5 min
Short answer
Slide the pot off. Compost visible between the roots means leave it alone. A network of roots following the pot wall, roots out of the drainage holes and a plant that dries out every day means pot on now, one or two sizes up. A hard felted mat with roots circling the pot shape means cutting — four vertical cuts down the sides and a slice off the base.
Potting on too early is as common a mistake as leaving it too late, and it causes root rot rather than solving anything. Reading the rootball tells you which situation you are in, and it takes ten seconds. The one thing that is not optional is cutting a genuinely pot-bound rootball, because a root that has begun to circle continues to circle in the new pot.
Step by step
- Look for the symptoms before you lift anything.A plant that dries out faster every week and wilts between waterings even when watered properly; water running straight through and out of the base without wetting the compost; growth that has slowed or stopped in the middle of the season; roots visible on the surface or emerging from the drainage holes; a pot that is unstable because the plant has outgrown it.
- Slide the pot off and read the rootball.Stage one, settled: compost visible between the roots throughout, a few white tips reaching the side and turning. Stage two, ready: an even network of roots following the pot wall, holding the block together. Stage three, pot-bound: a dense felted mat with little compost left, roots circling the pot shape and spiralling at the base, and the block holds the pot's exact form when removed.
- Leave stage one alone.Potting on now puts the plant into a volume of compost its roots cannot occupy, and that compost stays wet. This is a real cause of root rot and it is done with the best intentions.
- Pot on stage two, one or two sizes only.Roughly 3 to 5cm more diameter for a small plant, a little more for a large one. Use fresh compost, plant at the same depth it was growing, firm gently and water in well. Do it during active growth rather than in midwinter.
- Cut stage three before repotting.This is the step people flinch at and it is necessary. Four vertical cuts about a centimetre deep down the sides of the rootball with a knife or an old saw, a slice off the matted base, and then pull the outer roots outwards with your fingers. Teasing alone does not break a circling root.
- Understand why circling matters.A root that has started to circle keeps circling in the new pot and in the ground. On a tree or shrub it can eventually girdle the plant's own stem years later, which is a known cause of established trees failing. Cutting forces new roots to branch outwards.
- Root-prune instead if you want to keep the same pot.Take the plant out, cut away the outer few centimetres of rootball all round and off the base, reduce the top growth by a similar proportion, and return it to the same pot with fresh compost around it. This is standard practice for bay, olives, citrus and bonsai and keeps a plant at a manageable size indefinitely.
- Top-dress if the plant is too big to repot.Scrape off the top 5cm of compost each spring and replace with fresh, and feed regularly through the season. It is the accepted answer for large specimens in large pots.
- Water and settle it properly.Water thoroughly after repotting so the new compost is in contact with the roots, keep it out of strong sun for a week or two, and do not feed for six weeks — fresh compost carries enough.
- Know the exceptions.Some plants flower better slightly restricted — clivia, agapanthus, hippeastrum, streptocarpus and many orchids among them. Potting them on generously produces leaves and no flowers.
Tips
- Peat-free compost in a pot-bound plant is very hard to re-wet. Standing the pot in water for half an hour before repotting makes the rootball far easier to work with.
- Repot in spring or early summer where you can. A plant potted on in October sits in cold wet compost it cannot use.
- Do not add crocks or gravel in the bottom of a pot in the belief that it improves drainage. It reduces the usable depth and raises the saturated zone.
- A young tree or shrub bought in a pot should have its rootball checked and cut before it goes in the ground. Circling roots planted out stay circling.
Common mistakes
- Potting on into a much bigger pot to save doing it again — The unused compost stays wet, the roots do not reach it, and it rots. One or two sizes at a time.
- Teasing a pot-bound rootball instead of cutting it — A felted mat does not come apart by teasing, and the circling roots continue to circle. Cut.
- Repotting a plant that is wilting from root rot — That is a different repair. Check the roots first — soft brown roots need washing and cutting back, not more compost.
- Burying the plant deeper in the new pot — The collar should sit at the same level it grew at. Deeper is how basal rot starts.
Questions people ask
How often should I repot?
By the plant rather than by the calendar. Fast growers may need it annually, slow ones every three or four years, and large specimens never — top-dress instead. Checking the rootball each spring is the habit that answers it.
Can I cut a lot of root off without harming the plant?
A third of the rootball is routine when root-pruning, provided you reduce the top growth by a similar proportion and keep the plant shaded and evenly watered afterwards.
The roots are coming out of the drainage holes. Is that definitely pot-bound?
It is a strong indicator, though a root or two seeking moisture from a saucer is normal. Take the pot off and read the rootball rather than deciding from the outside.