I bought a fern at Walmart just a few weeks ago. It had been in the frost at least 3 times and they were going to pitch it out. I was wondering if anyone knows how to save a dying fern? It still has green leaves.
Does the plant label have any other information, perhaps a genus?
Ferns like water and humid conditions, so make sure it is watered. Not sat in water, but don't let it dry out. Also it will prefer a humid atmosphere - think bathroom rather than a dry office for example.
Many ferns are perfectly fine with frosts although they may go dormant like most plants in these conditions. Due to their water needs I tend to think of them as temperate plants (think of babbling wooded brooks in the British Isles, for example) - where frosts are common. But I've also seen them growing in the rainforests of Costa Rica - VERY humid but frosts are unheard of and would probably kill these species.
I'm guessing that you bought the fern from Walmart still in the pot? The cold may have gotten into the roots, which isn't particularly good. We have a lot of ferns here in Oregon and they get buried in snow or covered in ice, but they are just fine in the spring and summer. They survive winters by having their roots buried in the soil.
Best you can try to do is plant it or if you are keeping it in a pot, put it in part sun/shade and keep it watered. If keeping it in the pot, put it in a larger one with fresh composted soil?