I acquired a lot of ostrich ferns from someone who wanted to get rid of them. It was in May I think. The ferns were already large. I transplanted them immediately and tried to keep them watered. They have been turning dark and drying up, usually from the top to the bottom. What could be the reason for this and what can I do? I planted them under a tree in the shade in two different areas of the yard. One area gets some sun.