I have planted 6 - 8 native varieties of ferns over 4 years in a shaded area between two decideous trees that no longer supports grass. The west exposed area has a slight slope so I prepared amended holes on the clay slope and left an indentation to retain water when I am watering. They all did well the first year but none came back the following year. My hostas in that area grow nicely. I did not fertilize or mulch them as I have had ferns in other areas of the yard for many years that grow vigorously with no attention. What am I doing wrong?