Pruning Ornamental Grasses
By Steven Hightower, Sonoma County Master Gardener
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.
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
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.
Calamagrostis x acutiflora ‘Karl Foerster’ looks lovely with its tall tan seed heads through the winter, so it gets cut back to 3-4 inches in February or March. Miscanthus sinensis (maiden grass) gets cut to around the same height then too, as does the Nasella tenuisima (Mexican feather grass). This latter re-seeds easily, so watch out for it to move into areas of the garden where it’s not wanted.
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 (Berkeley sedge) and Festuca ovina (sheep’s fescue) as a tiny lawn-like area. They’ll get weed-whacked to 4-5 inches a couple of times a year.
That covers grasses in Top Plants, plus a few, but there are many more of worth. Some resources for further information include:
Missouri Botanical Garden