I have several ferns in my garden and some of them not doing to well,leaves are brown and soggy. But don't despair they are very hardy as i have one next to my pond.which i tried to get rid of last year by spraying it with roundup, it killed it or so i thought it's back this year (very suprised)

try giving it a sugary drink. Pour some sugar dissolved in water into the top as a way of giving it a boost. I tried this when I thought mine had died and now it's back. good luck.