Trimming Ornamental Grasses

Asked December 31, 2015, 6:22 PM EST

I live in Littleton Colorado at 6300'.
When and How Much do I cut back Ornamental Grasses?
We planted several varieties this summer: does the species matter?
If so please specify:
Karl Forester
Pompous Grass
Blue Oat Grass
Ribbon Grass
Switch Grass
and several others.

Thank you!

Arapahoe County Colorado

5 Responses

I'm an amateur and just a tad above sea level, but will try to help since your question has languished. Ornamental grasses can be cut back any time after die back (so when brown). Some owners appreciate the foliage during winter but others like to cut back before snow. Note that some grasses stand up better to winter winds and snow while others are more fragile so always disappoint. I like to retain mine until late winter since snow is usually light here. It is important to cut back the old foliage before new growth begins, so get out there on the first nice day in early spring. Some only cut back to 1' but I cut as close to ground as can to reduce brown feet. Thick stalk varieties are best knocked down with an electric hedge trimmer or bush wacker, while thinner stalk varieties can be cut with manual hedge shears. Good luck from a MD gardener.

Thank you so much! We definitely like the foliage, so will wait until later March. March is our snowiest month with April being the runner-up most years. We are curious, does Pampas Grass grow in Maryland? Again we appreciate your time and expertise (even tho' you claim not)! Connie

Tnx Connie. Remember that, counter intuitively, snow insulates plants from cold air so accelerates spring growth even though we associate snow with cold. You will undoubtedly see some flatten immediately from snow but others remain stout, at least for a while and/or in avg weather. So sched your maintenance according to each variety. Most importantly (sorry forgot to say before) if you are ever late with chopping prior growth, do not cut into new growth, since that would sentence you to a yr of looking at ragged tops - so much worse than looking at higher brown ankles.

MD has quite a range in topo/temps. I'm near Annapolis so mild temps since near bay tributaries. 25+ yrs ago i planted a dwarf pampas (pumila I believe) that was promoted as hardy. It lasted a few yrs but then died, but admittedly I never mulched it during winter. it is reasonable to assume that breeding has created a hardier variety(s) now but I have not researched it. Am surprised that pampas grass will survive in CO, but if it does, it surely would in MD.
No snow yet here and not a skier so really happy to be here!!! (but respect your choice!) Hope you keep your flannels and snow shoes near. ciao



Ornamental grasses are a great addition to our Colorado gardens. They tolerate a wide variety of soils, require little effort to grow and maintain, and they come in a wide variety of sizes, shapes and colors.

Some grasses grow best in warm temperatures (warm season grasses) and some grow well in the cooler temperatures (cool season grasses). Based on your list, you have a variety of both: Cool season: Karl Foerster, Blue Oat. Warm season: Pampas, Ribbon, Switch.

Whether it is a warm or cool season grass, they are generally cut back in early spring (March - April) before new growth begins.

After several years when your grasses need dividing, note that warm season grasses are divided in spring, cool season grasses are divided in the fall.

Here are some helpful links that will help you identify, maintain and eventually divide your ornamental grasses:

http://extension.colostate.edu/docs/pubs/garden/07232.pdf

http://www.colostate.edu/Dept/CoopExt/4dmg/Lawns/orna.htm

http://www.colostate.edu/Dept/CoopExt/4dmg/Lawns/ornacare.htm

http://www.ext.colostate.edu/ptlk/1068.html

That was very useful info, and I should have introduced the subject of eventual dividing. The digging of these grasses is laborious and a real downside to having them. Many varieties expand around the perimeter, which is good, but alas, the center dies. The standard response is to dig it up around the perimeter (which is a chore given very dense and deep root system), then quarter it, remove the old center, and replant a section in the old location while starting the others where ever, giving away, or trashing. +/-10-20 yrs ago i saw an alternative on tv. The gardener had hundreds of orn grasses, and when the core died enough to be unsightly, he cut out the core of dead roots with a chain saw (!), cleaned out the hole with a shovel, then filled it with good soil enriched with compost. He reported that this process was much less work and had reliably resulted in grass growing back into the center area. So an alternative to keep in mind. You sure are getting your money's worth, so don't let us down!
Good luck from a gardener in MD