Most ferns should be pruned in late winter or early spring, shortly before the growing season starts. Begin pruning ferns when they are 3 or 4 years old.
Look in the center of the plant to find newly growing fronds. Older fronds form a ring around the outside of the fern. These are the ones that need to be cut back.
Grip the frond firmly by the stem. Using a pair of pruning shears, cut it off as close to the base as possible. Repeat for all the old fronds on the fern.