A plant is root-bound, or pot-bound, when its roots have filled the pot and started to circle round the inside. Some plants tolerate this for a long time, but eventually it holds them back.
Clues you can see without unpotting: roots poking out of the drainage holes or pushing up through the surface; the pot drying out much faster than it used to, so you are watering far more often; water running straight through without seeming to wet anything; lower leaves yellowing and growth slowing even in the growing season; a plant that looks far too big and top-heavy for its pot.
To be sure, look. Water it a little while beforehand, then tip the pot on its side, support the base of the plant between your fingers and slide the root ball out; tapping the rim helps. If you see a dense mat of roots circling the outside with little mix left, it is time for a bigger pot. If you see plenty of mix and a few roots, slide it back and wait.
Careful: yellowing, leaf drop and slow growth can also mean too much water. Checking the roots tells you which.
Key points
- Roots out of the holes and very fast drying are classic signs.
- Slide the plant out and look: circling roots and little mix mean repot.
- Similar leaf symptoms can come from overwatering, so check the roots.
Try this
Choose one plant that has been in its pot for over a year. Water it, and a few hours later gently slide it out to look at the roots, then put it back.
Check yourself
Read more in the reference
Sources
Marking a lesson done is kept on this device only.