My 3-or-so-years-old bird of paradise plants have reached about 2.5 feet tall, but as new leaves grow, the oldest ones die, so that all that I ever have are 2-4 healthy leaves. In detail: The oldest leaves (on the outside) turn brown and wither. They look like they are drying up, but the soil is in fact well-watered, and the plants are in a room with high humidity so that isn't what is happening. Slowly, over the course of a few months, they become completely withered. Finally I cut them off, leaving 2-3 new, taller, healthy leaves. Then new leaves start to grow - and now the leaves that I have just described start to wither in turn and the cycle repeats! At this rate I will end up with 5 plants each consisting or two or three 5 foot tall leaves. I have never been able to understand this, but the plants' 8" pots are starting to bulge on the bottom and it has crossed my mind that maybe the plants are too rootbound and are not getting enough nourishment to support many leaves. Does anyone know if this might be so? Or does anyone have any other explanation for this phenomenon?