HI Woofie and everyone, just my two cents worth here.
If you live in a marginal area where Tree Ferns will do well, and if you want to carry them over the winter outside, there are several methods that I've read about that people have used to protect them from the cold. It is very very important to keep the growth point protected. If that freezes then the plant is a gonner, especially if water gets into the center and then freezes. Many people wrapped their ferns with straw and then wrapped with burlap covering the growing point with something that will shed water and then putting burlap over it again, making sure that everything is tied down securely. As long as that growth point is protected from freezing it will survive, -26 once in a while. Other's take it one step further and wrap the large Christmas lights around the stem and turn them on providing a small amount of heat around the plant it's self. Also, soom actually erect a tent around the plant itself using thick plastic sheets stappled to wooden poles and then have the lights around the plant. Also if your not too tidy of a person, leave the old fronds on the plant allowing them to drape down and around the lower stem. It actually provides insulation as the layers increase over the years and also helps keep the humidity around the trunk as well. Hope that helps as well.
