I've been growing a couple of sea grapes indoors in a sunny window here in PA for the last two years. They have done very well - until about six months ago. They grow leaf buds, and whether small or large, they fail to open. Some of them have just been sitting, not opening, for many weeks. Others have slowly turned black - then a new bud tries to grow off the dying one, until it too dies and turns black.

There is no symptom of disease or insects other than this problem. The only thing I can think of is that the roots may be getting crowded - could that cause the leaves to die in the bud? Of course, this is normally not a house plant, so I haven't been able to find any references to something like this online.

I'd be grateful for any explanation.