I pretty much neglect mine as far as fertilizer, they just seem to need very little care here. But I do have tons or organic matter in the soil, other than that and water I really don't have much advice I am afraid.
Edited to add:
http://edis.ifas.ufl.edu/ep060
They suggest maybe the soil is too rich? Too much shade? I suppose the amount of shade could be dependent on the intensity of the sun, down here sun may be much more intense? Don't know.
