Master Gardeners are a statewide, even nationwide, community of people who love to garden and who willingly share what they've learned in an effort to make gardening inclusive, enjoyable, and fulfilling. In this larger community of like-minded people, we often share articles with one another. This article is one that was developed by a Master Gardener from Sonoma County and is timely for our Spring Newsletter.
Pruning Ornamental Grasses
Ornamental grasses have become increasingly popular in home landscape use. Recent books such as Richard Darke's Encyclopedia of Grasses for Livable Landscapes and John Greenlee's American Meadow Garden promote them, as do many gardening magazines. We have several in Top Plants for Sonoma County, and I've increasingly used grasses in my garden over the last few years.
Ornamental grasses are generally low maintenance. Once established, most only need periodic combing, and sometimes, depending on the variety, an annual cut-back. General advice often states to cut them back in the fall, but here, where our winters are mild, many can provide texture, contrast and color in the winter garden, so I often leave the chore until early spring.
For grasses that are to be cut back hard, it's easiest to wrap the whole clump with a piece of twine—some suggest masking tape—and then cut below that with well-sharpened shears. An old web or leather belt works great and is re-usable. That way the whole bundle of grass comes away clean without leaving a mess of stalks. Larger and tougher grasses may take a hedge trimmer, or even a small chainsaw. Which then to whack, and which to leave?
The lowest-water grasses I have are Muhlenbergia rigens (deergrass), Festuca californica and Festuca idahoensis. With little water in the summer, these survive, but brown up quite a bit. I comb the dead material out a couple of times a season—a small fine hand-rake works, but rubber-gloved hands work even better—run your gloved fingers from the base of the grass to the top. And they get cut back to a few inches (not flush to the ground) around February, but not necessarily every year. Muhlenbergia capillaries (pink Muhly grass) should also be sheared fairly low in early spring.
I love blue grasses. Festuca glauca (blue fescue) and Helictotrichon sempervirens (blue oat grass) are great performers, and don't need to be cut back very often, but should be glove-combed out periodically to keep them looking good. A great fescue that I recently discovered is Festuca mairie (Atlas Fescue) and it gets treated the same way.
Pennisetum orientale ‘Tall Tails' (oriental fountain grass) is another of my favorites – it's similar to the more common P. orientale, but stands 4-5' and works well in a tall perennial border. I cut it back before the new growth starts to appear, but after the cold weather is over—again, February or so. Cut back to about 3-4 inches above the crown of the plant. For Sesleria autumnalis, cut the clumps back in the spring to encourage new grow growth and to maintain good form and habit.
I've recently planted some Carex pansa (California meadow sedge) and Festuca ovina (sheep's fescue) as a tiny lawn-like area. They'll get trimmed to 4-5 inches a couple of times a year.