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Wednesday, November 2, 2022

Leave Ornamental Grasses Alone Until Spring by Nancy Shepard

 

Ruby Muhly Photo: Plant Select

As we see plants in our garden die off, some of us might have the urge to tidy everything up. One of the plant categories that can benefit most from a hands-off approach are the ornamental grasses.

There are many reasons to leave these grasses standing over the winter months. Their foliage and seed heads offer texture, movement, and beauty in the winter. They'll also be illuminated by the low angled winter sunshine. Plus, many beneficial insects use these grasses to provide protection for overwintering egg masses, larvae, and adult forms. Leaving ornamental grasses standing until late spring gives the insects time for their eggs to hatch and their larvae to change into adults. Birds will also use standing grasses as sources for seed and winter shelter.

There are basically three types of ornamental grasses: Warm-season grasses that begin growing in mid to late spring (warmer temperatures); Cool-season grasses grow best when temperatures are cooler, between 60-75 degree F, which is why they grow most actively in the spring and fall; Evergreen grasses remain mostly green through the year and do not need to be cut back.

Blonde Ambition (Grama Bouteloua) 
Photo: Pexels Doreen Wynja
Warm-season grasses begin growing in mid to late spring, or even early summer. They thrive when the temperatures rise, with major growth and flowering occurring during summer's heat. Warm-season grasses turn brown in winter. Warm-season grasses should be cut back in mid-spring. This will protect the crown of the plant, and encourage new growth as temperatures warm. The exception to this is areas of high fire danger where you should prune them after they go brown. Warm-season grasses include Little Bluestem (Schizachyrium), Big Bluestem (Andropogon), 'Blonde Ambition' Blue Grama (Bouteloua), Muhly (Muhlenbergia), Switchgrass (Panicum), Maidenhair Grass (Miscanthus), Giant Sacaton (Sporobolus wrightii.) Other common warm-season grasses include northern sea oats (Chasmanthium), Japanese silver grass (Miscanthus sp.), hardy pampas grass (Erianthus), perennial fountain grass (Pennisetum), switchgrass (Panicum), and prairie cordgrass (Spartina). When you prune these warm-season grasses, cut them severely, right down to the ground.

Karl Foerster' Feather Reed Grass (Calamagrostis).
Cool-season grasses have evergreen foliage that should not be cut to the ground. Instead, vigorously "comb out" dead leaves with gloved hands and clip off the dead leaf tips in late fall. Then in very early spring, cool season grasses should be cut back. As soon as the snow clears, cut the grass back by two-thirds, leaving one-third in place. Pruning too drastically can harm the plant. Some examples of cool season grasses include fescues, blue oat grass (Helictotrichon), tufted air grass (Deschampsia), and autumn moor grass (Sesleria.) In early spring, clip off old seed heads from stalks as far down into the foliage as possible to leave room for late spring flowers. Other cool-season grasses include Blue Avena Grass (Helictotrichon), Fescue Grass (Festuca), Silky Thread Grass (Nassella) and 'Karl Foerster' Feather Reed Grass (Calamagrostis).

If you have evergreen ornamental grasses, don’t cut them back; instead, simply remove the old leaves or blades in early spring. Examples of evergreen grasses are sedges (Cyperaceae,) and blue oat or avena grasses (Helictotrichon sempervirens.)

Giant sacaton(Sporobolus wrightii)
Photo: Plant Select
If the grass plant has a ring of living leaves with a dead center, it's time to divide the grasses to re-invigorate them. This is necessary once every three to five years depending on the species and growing conditions. 

The following were used as sources and have very good information about ornamental grasses:

https://extension.colostate.edu/topic-areas/yard-garden/ornamental-grasses-7-232/?fbclid=IwAR2WhY7eyrOF6-wtWizXquL3mNTBRn4RIsWH9PqDoZEHXKtpNgzXgmhoXfw

https://www.highcountrygardens.com/gardening/fall-garden-clean-up-dont-prune-these

https://web.extension.illinois.edu/grasses/

https://gazette.com/news/ornamental-grasses-need-cutting-back/article_a093036e-79bc-5fe8-8288-36b8f73a64db.html

https://harlequinsgardens.com/plants/ornamental-grasses/