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.
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.