I bought two Holly Trees recently and put them into planters. One has prickly leaves, the other smooth. Initially they wer both doing well, but now after 4 months, the leaves are starting to fall off the smooth leaved one. Could anyone advise what might be causing this? I can't see any plant pests on the leaves. I have put some slug pellets around it, as a precaution. We do have quite a lot of cats in the area. Could they be killing it off by peeing on it?
Holly hates having its roots disturbed. It can develop what's called 'transplant shock', where, as in your case, all the leaves fall off. But don't worry, they'll re-grow eventually. Keep the soil moist, but don't over-water.