I have questions on general maintenance for the ferns in my garden. It is winter and the wood ferns (now about 4 feet in diameter) have fronds which are now partially brown. The deer ferns look similarly forlorn.
Should I prune all the old fronds off and let the new ones take over? How and when to do this without damaging emerging new growth?
Sources are divided on when and whether to prune wood ferns (Dryopteris). Some consider Dryopteris “self-cleaning,” meaning that the old fronds will eventually disintegrate on their own (Gardening with Woodland Plants by Karan Junker; Timber Press, 2007). If you are inclined to tidy up the look of your plants, they can be pruned of their old fronds after new growth begins in the spring (this can be risky: be careful not to cut the new fronds), or according to Pacific Northwest sources, in late February or early March before new growth starts. Rainyside Gardeners and Great Plant Picks, two Pacific Northwest resources, offer more information. Rainyside advocates pruning once there is new growth, and Great Plant Picks advocates pruning before new growth begins. The same is true for deer fern (Blechnum spicant, now renamed Struthiopteris spicant): “Old fronds should be cut back in late winter or early spring before new growth starts.”
This is a good general guide for pruning maintenance of ferns, written by Richie Steffen of the Hardy Fern Foundation. The first thing he points out is that cutting back ferns is purely an aesthetic choice; it is not necessary. If you do want to cut back, consider the type of fern: is it evergreen, winter-green, deciduous, or semi-evergreen? The answer to this question will determine the best practice.