my problem with coconut fiber is that it shrinks a LOT if the humidity drops. the package says that the brick-sized lump will expand to over 1 cubic foot when wetted out, and this is true. but as it starts to dry out, it will go back to being brick-sized. i no longer use it even as a small constituent of potting soil, because there is no way i can keep a pot (much less a planter) at a constant enough moisture level, even indoors.
you may have better luck inside a mostly-sealed paludarium, where you can hold the humidity fairly constant, but i recommend using something else
