Recently, we were asked if ornamental grasses need to be trimmed down in the fall. The answer to that begins with a look at your garden or landscape design with an eye for purpose and aesthetics. With the bulk of your garden dying down for a cold and snowy New England winter, the grass fronds left may add interest and texture, serving as a focal point in an otherwise gloomy landscape. The seed pods produced by the grass provide food for winter birds and the grasses themselves provide protection for birds and small wildlife. This progression of birds and beasts through your garden may serve as winter entertainment -- enough to warrant leaving the grasses in full growth.
But if you've got your sights set on spring, making it through another winter only to burst forth into spring cleanup and gardening grandeur, cutting down your ornamental grasses may make for an easier spring cleanup. As grasses fall prey to cold temperatures and snow, they can become messy, increasing the time it takes to clean out your garden of debris in the spring, in preparation for new growth.
Cool-Season vs. Warm-Season Grasses
All grasses grow through an underground root system that spreads a thin layer and shoots up stems at intervals that are either spread out, as in lawn grass, or condensed, as with ornamental grasses. These clumps of grasses are what add interest to landscape design. Warm-season grasses are slow to begin their growth in the spring, flowering late in the summer. Many will look good and hearty well into the fall. Most warm-season grasses will turn brown in the winter. Examples of warm-season grasses are perennial Fountain Grass, Indian Grass, Maiden Grass, Dropseed and Switch Grass.
In contrast, cool-season grasses begin their growth early in spring, as soon as temperatures rise above freezing. Some cool-season grasses remain evergreen through the cold months, reaching their peak of color during the active growing spring season. When summer arrives, their growing season slows down, and they are past their peak of color and foliage provided at the beginning of spring. Examples of cool-season grasses are Blue Fescue, Feather Reed Grass and Blue Oat Grass.
Cool-season grasses seem to need a bit more care than their warm-season counterparts. They will benefit from cutting back in the fall, and will look best if divided in the spring. Grasses put on new growth around their perimeter. If left undivided, they will eventually die out in the center. Fall, however, is not the time to divide grasses. Save that chore for early spring.
Bottom Line on Fall Trimming
The mess is the test. If you are looking to maintain an orderly appearance in your garden, and don't want the spring hassle of raking up soggy plumes and stems, cutting grasses back by two-thirds of their height will get them through the winter neatly and ready for new spring growth.
Nurture nature. On the other hand, leaving ornamental grasses standing through winter will do no harm to the plant, provide protection for birds and small creatures, and spent seed pods will provide feed for birds.
Calculate Cut by Warm vs. Cool
If you decide to trim down your ornamental grass, cool-season grasses should be cut back by two-thirds of the height of the plant, while warm-season grasses can be cut down to the ground. Keep in mind that the clump style of roots that support ornamental grasses is very hearty. There is no need for foliage to help insulate them through the winter.
Hint: Before cutting, first tie your ornamental grass into clumps. The grass fronds and stems can be thick and you'll most likely need to cut through sections at a time. Tying it up first will cut down on the mess you'll need to clean up afterwards.