Check the Roots
A good root system is like a well-maintained engine, and if an established plant doesn't have one, don't touch it. First, try to slide the plant out of the pot (not always that easy) and check that there’s a good all-around spread of roots. Avoid pots where congested, restricted root growth means you can't see any soil, a problem known as \"pot-bound,\" and/or when the roots curl out of the drainage holes and make a knotted clump. Being cramped like this invariably signals poor and sickly top growth.