There's so much more to a great yard than just mowing the lawn.

Time to cut back the Karl Foerster

Break out the pruners. It’s time to get busy!

Karl Foerster feather reed grass (Calamagrostis  x acutifolia ‘Karl Foerster) is the most common ornamental grass planted in Colorado landscapes. It’s upright, tidy form and blonde seedheads make it a very popular plant. Since it’s so common, it’s helpful to know how to care for Karl Foerster feather reed grass.

Here’s a video I posted about the best ways to cut ornamental grasses back in spring. These methods work great for Karl Foerster.

Timing

This ornamental grasses greens up earlier than most. That means you need to cut it back early to prevent the new growth from mixing with last year’s blonde (dead) stalks.

Normally, I recommend cutting it down between February 1 and March 15 along Colorado’s Front Range. If you live in Denver or a low elevation city, cut it back in early February. You need to cut it down earlier because it will start to grow earlier in the year than higher locations. If you live in a higher elevation community like Monument, you can wait until mid-March. Most years, it’s already growing rapidly by April.

If you haven’t already, now is the time to cut it back. After that fantastic snow this weekend, it’s easy to think that spring is months away. However, the first warm stretch will cause Karl Foerster to start growing new leaves. Cut it back before it starts growing.

This year, things are a little different. Due to the colder than normal February and March we’ve had, its growth has been delayed. That means it’s not too late to get a good cut. Nonetheless, as soon as it’s comfortable to work outside, cutting down the Karl Foerster grass back should be a top priority.

How to do it

Cut off all the growth as close to ground level as you can. Last year’s growth will never green up again, so it’s best to remove it completely from the plant. Cutting as low as practical means you’ll have a green, clean-looking ornamental grass to enjoy all summer.

A pair of hand pruners or a hedgetrimmer are great tools for this job. As I mentioned above, here’s a video where I demonstrate my preferred methods to cut back Karl Foerster feather reed grass. You can also check here for ideas on what to do with the old growth.

What not to do

Don’t leave 6-12 inch stubs of last year’s growth. There’s no reason to do this, even though it’s an extremely common practice. Just take a look at any strip mall. Leaving stubs doesn’t benefit the plant at all. In fact, it makes the base of the plant look strange all summer, with the new growth mixed in with the old. Instead, cut clean and cut low. Here’s a post from later in the summer that shows the outcomes of different pruning approaches.

A bit of history

Karl Foerster feather reed grass was named after the famous German plant breeder and nurseryman, Dr. Karl Foerster. That’s where the foreign spelling comes from. He became well known for mixing informal plants (like ornamental grasses) into German landscapes. Despite how popular it is now, this effort was quite revolutionary for his era.

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10 Responses to Time to cut back the Karl Foerster

  1. Michelle June 26, 2015 at 8:23 am #

    Hello,

    After a hard rain storm last night my Feather Reedgrass has fallen over, should they be cut back… & if so, will cutting them back harm them for future growth?

    Thank You,
    Michelle

    • Catherine June 26, 2015 at 10:56 pm #

      Hi Michelle, I find in most cases when an ornamental grass flops during the summer due to hard rains, if you wait a few days it will gradually pop back up. If there’s still some leaves laying down after a week or so, you could selectively cut those out if they don’t look good. If the whole thing is flattened and doesn’t look like it will stand back up this summer, you could cut the whole thing back. I don’t think you’d be harming the long-term health of the grass, but you will probably sacrifice some height and maybe the seedheads this summer. It may regrow somewhat, but probably won’t reach its normal height before fall arrives. Be sure to let us know what course you take and how it works out.

  2. Kim May 12, 2017 at 4:33 pm #

    What happens if you miss the ideal window? Should you not prune at all, or prune late (May)? We have only been in Colorado for a few years, and just discovered your very informative website, and to my knowledge our Karl Foersters have never been pruned. Thank you!

    • Catherine May 14, 2017 at 2:03 pm #

      Hi Kim, great question! If it were my yard, I would go ahead and cut the Karl Foersters to ground level even in late May. There’s still a lot of growing season left this year. They may not get as tall as normal, but cutting them back will remove all the old growth and give the new growth a chance to get much more sunlight. That will help them be more vigorous in future years; not to mention, they’ll look better, too! If it were late summer (August or September) when their growth rate has slowed down considerably, I’d recommend waiting until the following spring. Just make sure you water them regularly after you cut them back so they can regrow quickly.

  3. Mag June 17, 2017 at 7:18 am #

    Our Karl Foresters seem to have gotten far taller than expected. To keep them a little shorter, next year can we trim the height back before the seed heads show?

    • Catherine November 6, 2017 at 12:04 pm #

      Hi Mag,

      Sorry I didn’t see your question earlier. Yes, you can control the height somewhat by cutting them back periodically. I would try to do that once they’re about 6 to 12 inches tall and let them regrow from the base. If you wait too long, you’ll see the cut foliage all summer or they won’t bloom well.

      Another option is to replace them with a shorter grass. Blonde Ambition blue grama grass and Undaunted ruby muhly are two grasses I’ve had great luck with recently. Hope that helps!

  4. ashly mcqueen June 18, 2017 at 6:22 am #

    Help! All of my grasses like mentioned above have new growth and the rest is dead to wear I cut it. I now realize I wasn’t doing it right. I was cutting it down to about 6 inches to ground and guess leaving the old from previous years. The past couple years I have been doing it wrong. So now what? Do I cut that old to the ground or wait? There are about 12 of them that frames my front yard and it’s an ugly sight when it used to be beautiful.

    • Catherine November 6, 2017 at 12:06 pm #

      Hi Ashly,

      Sorry for not replying sooner, but I wouldn’t cut them back again mid-summer. Just start cutting them to ground level the next time you cut them back. I’ve done this a lot on plants I start maintaining after they’ve been planted for a few years and it works well. If they’re very old, it might be worth dividing them when you cut them back in late spring to remove any dead center that’s developed. Good luck with your gardening!

  5. Larry October 5, 2017 at 8:08 pm #

    Hi
    We live in Canada so we get into our winter around November.
    Should we cut it down in the fall or spring? (Karl Forester)
    ThankYou
    Larry

    • Catherine November 6, 2017 at 11:58 am #

      Hi Larry,

      In Colorado, we cut them back in spring because they look so nice over the winter when everything else is brown. We also get heavy snow only occasionally, so they don’t get crushed regularly. In areas where heavy snow is a regular occurrence, most gardeners cut their ornamental grasses back in the fall. So, it’s really a matter of personal preference. Your grasses will be healthy either way, as long as you cut them back before they start growing again in spring.

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