Answer: Fern care depends upon the type of fern. For instance, the native sword fern can be cut down to ground level at any time without causing harm. Maidenhair fern typically dies down after the first frost, so they are generally allowed to grow at will during the spring and summer months. As with all plants, ferns look best if groomed throughout the growing season by removing dead or injured fronds as close to ground level as possible. In my Seattle garden our first hard frost arrives in mid-November. This kills the fronds, but I leave the dead foliage on the plants over the winter months to help protect the crown from winter weather. In the spring I cut away the dead foliage to make room for healthy new growth.
The tree and fern litter on your property is useful for both plants and soil. It serves as a natural mulch, protecting roots from cold, plus it returns nutrients to the soil as the debris breaks down. Your trilliums and ferns rely on this protective mulch to help them get through the winter. I understand your desire for a neat and tidy garden, but a woodland garden should have some debris left under the trees. Not only does the debris make the garden look more natural, it provides food and shelter for wildlife, and helps regulate soil moisture. A better approach would be to clear path-sized swaths on the forest floor for ease in strolling around the garden, but leave the majority of debris where it falls.
I suspect the ferns under your deck or the native sword ferns (Polystichum). These plants grow with great abandon and older plants can spread up to 4' and have 75-100 fronds attached. The roots are deep and tightly knit, making them difficult to dig. They recover quite readily, though, so don't worry about injuring the roots by digging each massive clump and dividing with a shovel. Replant the divisions and they'll take off next spring and summer.
Best wishes with your woodland garden!
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