pot-bound 
adjective
(Of a plant) having roots which fill the flowerpot, leaving no room for them to expand: pelargoniums seem to flower better when pot-bound...
- Skip these pot-bound plants because the roots will be torn off during transplanting, and could cause a major set-back.
- Loosen the roots of pot-bound nursery plants before planting them in the garden.
- Look for a grass that has colorful foliage and is not too dense, which indicates that the plant has already become pot-bound and might be difficult to establish if planted.