Q.Boston Fern Roots Black In Color
Potong soil for fern and the leaves brown ing and falling off
Certified GKH Gardening Expert
It sounds like an infection in the soil. Make sure that the soil remains moist, but never wet or dry. It should fluctuate, slightly.
From here, you will need a fungicide, and to keep a close eye on overwatering, or saturated soils. This can suffocate plant roots, leaving them open to infection.
These articles will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/houseplants/boston-fern/boston-fern-care.htm