I pulling this message up from a while back, because I have the same questions. What is the best soil for ferns in containers? The ferns that interest me will be transplanted from a woodland garden with high-hummus, moist but not boggy soil.

I pot up the more common ostrich fern each year for my porch. I use the soil it lives in, in my garden. I have best results taking very little new ferns. I have noticed as I begin a new, the next year the root system of these is extensive. It would be tough to add new to last years pot w/o starting over completely. I am careful to make sure the dirt stays moist, other then that they are pretty care free.