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Update on Karl Foerster

Karl Foerster Unpruned

When Karl Foerster feather reed grass is not cut back, the new growth becomes tangled with last year’s growth.

Back in March I wrote a post about cutting back Karl Foerster feather reed grass. Just like those television shows that follow up with child actors later in life, let’s take a look at how these ornamental grasses are doing today. After all, which actions you take in spring will affect how healthy and attractive these plants are down the road.

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

No action taken

Here’s what Karl Foerster grass looks like if it’s not cut back in spring. The new leaves simply grow up into the old, dead growth.

Keep in mind the brown stalks are completely dead. They will never green up ever again. That’s why I recommend removing them as close to the ground as possible between February and March.

If you have a Karl Foerster grass that wasn’t cut down in spring, you have two options. The first option is to leave it until next spring, when you can cut it down to the ground.

The second option is to cut it to the ground now. It’s likely the grass will slowly grow into a green mound before the fall, which will give it a tidier appearance eventually. However, it probably won’t have time to produce seed heads before winter arrives. It will just be a mound of leaves. You could then cut it back in spring, which will allow the grass to grow normally from then on. This is a better option if you don’t think you can tolerate the current state of affairs all the way until next spring.

Karl Foerster Cut to 12 Inches

When the grasses are cut to 12 inches tall in late winter, too much brown growth remains for the summer.

Cut a foot above the ground

Karl Foerster Cut Too High

Karl Foerster grasses cut too high look awkward all summer.

It’s extremely common to see ornamental grasses cut about a foot above the ground in late winter. I’m not exactly sure why this became the standard practice in Colorado, but here are the results.

Early on, the new leaves start to grow up into the old growth, but then they reach a point where they are taller than last year’s growth. The result is a mixture of brown stubs and green growth. I think these plants could look better.

Later in the summer, you notice that the stalks that have grown this summer are beginning to flower. But look what’s very noticeable on each one of these grasses. Yep, last year’s growth. Cutting back ornamental grasses too high above the ground detracts from their appearance for the entire year.

 Cut to ground level

Karl Foerster Cut to Ground

When Karl Foerster grasses are cut to ground level in late winter, all the old growth is removed.

Ah, the eye can rest. When Karl Foerster feather reed grass is cut as close to the ground as possible, you remove as much of last year’s growth as possible. The result is new leaves growing without anything blocking them. The plant looks green, attractive and healthy. It will still achieve its famous upright form and gorgeous blonde seed heads. It doesn’t need last year’s growth to hold it upright; it naturally has strong stems.

So early next spring, revisit these results. Give cutting back to the ground a try for beautiful results next summer.

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23 Responses to Update on Karl Foerster

  1. Steve kurtright July 19, 2014 at 4:09 pm #

    Question re: Karl Forrester grass. Just noticed middle disappearing in a couple days time. Have lots of rabbits. Could they be eating? Any other reason could be dying all of a sudden?

    • Catherine August 19, 2014 at 9:57 pm #

      Yes, rabbits could certainly be the culprit. They love to eat ornamental grasses, in my experience. I’ve seen them decimate Karl Foerster, blue avena grass, blue grama, switchgrass, Kentucky bluegrass, buffalograss, you name it. They usually don’t kill the grass, but keep it mowed so short it can’t ever gain any height. Here are two solutions to consider. First, I’ve had success caging desired plants with hardware cloth early in the growing season. The cage needs to be about two feet tall. If you use chicken wire, the little bunnies can get in and out. It has to be a small mesh. Once the grasses get to be about 18 inches tall, you can take the cage off and the rabbits won’t bother it much. I’ve also had good luck with an animal repellent spray called Bobbex. It’s pricey and VERY stinky, but will work if you don’t want to look at caged grasses all spring. Just make sure you buy the “animal repellent” with the bunny on the label, not the deer repellent. Let me know what works!

  2. Vicky November 9, 2014 at 6:38 pm #

    Just followed your advice and cut my Karl Foerster grasses to the ground. They are mature 5+ years old and have had the gardner and myself leave 6-8″ stalks as that is the original info I found for care on the web. However, I agree that they don’t look as good with all that old growth mixed with the new growth. The other issue I’ve had is continued widening of the plant. Will cutting it down to the ground help this problem? I what is the best way to approach narrowing the girth of my grasses? Thanks for your help, Happy I found your website 😉

    • Catherine November 11, 2014 at 10:10 pm #

      Hi Vicky, glad you found the information and are giving the advice a try. Cutting down the plant will not help the widening problem; that’s just the way most ornamental grasses grow over time. The best way to deal with the widening issue is to divide the grass into smaller pieces. I like to do that in spring after I’ve cut it to ground level. Simply get a sharp shovel, dig up the remaining top growth and root system of the grass, and cut it into a couple of sections. If the grass had turned into a ring with a dead center, cut dead portion of the ring off of each section. Replant one of the sections to replace the original grass. You can either plant the remaining sections in another location, pass them along to a friend, or compost them. In my experience, Karl Foerster feather read grass needs to be divided every 3-5 years in Colorado to stay vigorous. Please let us all know how it turns out!

      • JAKE November 12, 2015 at 12:30 pm #


        We have many apartment complexes in CO and have these Karl Forester grasses planted and we love them. The interesting this is, is that some of their plumes grow tall, and some have smaller plumes in regards to height.

        Could this be a fertilization problem, water or am I getting a different variety installed and told it’s the same? We enjoy the taller plume look and the dynamics it bring to our landscaping. Your thoughts?



        • Catherine November 17, 2015 at 1:43 pm #

          Hi Jake,

          Great question. In my experience the reason for the shorter plumes on Karl Foerster grasses could be one of the following: 1. too much shade, 2. not enough water, 3. the soil is compacted, or 4. not enough fertilizer. Karl Foerster needs at least 6 hours of sun to bloom well. If you have sites with fewer than 6 hours of sun, I’d recommend Korean feather reed grass (Calamagrostis brachytricha), which can bloom in full shade if watered regularly. In terms of water, Karl Foerster grass will stunt if it’s too dry. It needs to be watered at least twice per week, usually. Soil compaction is very common. In compacted soil, air and water cannot move freely so plant growth suffers. To test for compaction, water the soil. The next day, try to stick and hand trowel or shovel in the soil. If you feel more resistance than in areas where the grasses are growing well, it might be worth deep forking the soil to loosen it.

          To see if a lack of nutrients is the problem, you could either get the soil nutrient levels tested at a professional lab or try adding some fertilizer to a few struggling plants to see if it helps.

          I doubt that it’s a different variety. There is a cultivar called ‘Overdam’ that is a bit shorter, but you would notice white stripes along the edges of the leaves.

          Good luck, and let me know what you discover. I’m sure there are others out there with the same problem that would love to hear your results!

  3. Holly March 21, 2016 at 8:08 am #

    New to this gardening thing, and learning as we go! We built a home 16 months ago, and had all new landscaping put in last spring and we continued to add through summer – we live in the mid-west. I just cut back our Karl Foerster yesterday, and I left 6-8″ because about 4-5″ of new growth is already there and I was concerned about cutting the tops of the new growth. Is it ok to go ahead and cut it to the ground, even now? Thank you for your help!

    • Catherine April 1, 2016 at 9:15 pm #

      Hi Holly, I think either way is okay, especially since they are new plants. If you want to be more conservative, it’s fine to leave them as they are. This choice will leave you with a few brown stems throughout the summer, but you can cut them to the ground next spring. On the other had, if you’d really like a cleaner look, you can cut them to the ground. You’ll end up cutting off the tips of the blades so that rather having pointy ends, they’ll have flat ends for the year. Either way, the long term health of the plants should be just fine. Glad you’re seeing out information, and welcome!

  4. Patricia Rufledt April 27, 2016 at 5:14 am #

    Hi Catherine, I bought 4 plants in early spring last year at our local home improvement store. They were tagged Carl Forester grass but none of them produced any of the tall reeds! I thought maybe it was because it was their first year but they grew beautifully. I cut them back in the fall and they’re coming up now but no sign of the reeds again. Do you think they were tagged wrong?

    • Catherine May 6, 2016 at 8:44 am #

      Hi Patricia, that’s a great question. It’s possible they were tagged incorrectly, but I would be surprised if that was the case since Karl Foerster feather reed is such a common plant. Most of the time I see unusual plants with the wrong tags. It might be worth really inspecting the leaves to see if they look close to Karl Foerster leaves, meaning emerald green, outward arching, about 1/4 to 1/2 inch wide.

      In my experience, it can take them a season or two to flower, so it might be worth giving them another year. Also, sometimes Karl Foerster won’t flower if it doesn’t get enough water (which stunts it). Another possibility could be that it’s not getting enough direct sun to promote flowering. So, maturity, water and sunlight can all be factors. I’d love to hear what happens, so please keep in touch.

      • Patti Rufledt August 3, 2016 at 5:12 am #

        Hi Catherine, I had to let you know that my Karl Foerster grass is growing and beautiful…complete with reeds! You were right; it just took mine until their second season to flower. Thank you for your help!

        • Catherine August 3, 2016 at 1:15 pm #

          Hi Patti, that’s great to hear! So glad to hear there was nothing wrong with the plants. I guess patience really can be a virtue. Thanks for letting me know.

  5. Marie Harrison July 30, 2016 at 4:19 pm #

    I bought 3 Blonde Ambition Grass and planted them. the next morning the rabbits ate them down to the ground before I had a chance to put wire around them. My question is, will they grow back again and bloom next year if I protect them from rabbits?

    • Catherine August 1, 2016 at 12:32 pm #

      Hi Marie, yes, I think there is a good chance your grasses will regrow if you cage them for protection. In my experience, it’s the repeated rabbit grazing that kills new transplants. With blonde ambition, it may be wise to leave the cages on through next spring until the grasses have put on a bit of growth. The rabbits seem to like that one!

  6. Jon December 4, 2016 at 11:53 am #

    Hello Katherine,

    Thanks for the info on cutting back Karl Foerster. Can you provide advice on just when and how much to cut back Porcupine grass and also Prairie Sky Switch Grass?


    Jon Bowers

    • Catherine February 10, 2017 at 1:19 pm #

      Hi Jon, great question. I cut all ornamental grasses back as close to ground level as is practical. I find that works the best in terms removing all the old growth. As far as when, with maiden grass (porcupine grass) and Prairie Sky switch grass, they both green up quite late in Colorado. So, I try to get to it by April 1 depending on how warm the spring is. You can cut them down as early as you like with the knowledge that they won’t begin growing until late April or May. The only start growing once the soil temperature really starts to warm. Hope that helps!

  7. Mark May 19, 2017 at 6:38 pm #


    We recently purchased and planted a number of Karl Foerster grasses. They were young plants approximately 12-18 inches tall and during transport home in an open truck many of the grass blades were bent from wind. Should these blades be trimmed?


    • Catherine May 21, 2017 at 6:03 pm #

      Hi Mark, I’ve done that very same thing myself. One idea to consider is to cut off the top 6 inches or so to make them stand up a little better, but I would try to leave most of the blades in place even if they are damaged. The reason is that the leaves are where photosynthesis occurs, which will allows the plant to produce enough food to grow a strong root system. If you cut off a lot of the leaves, it will shock the plant. It will have to use it’s energy reserves to grow new leaves when it should be growing new roots. Once you start to see new leaves growing, it’s fine to cut off the ugly ones. Hope that helps!

      • Mark May 21, 2017 at 6:06 pm #

        Thanks so much. All the best.

  8. Mickey October 2, 2017 at 12:33 pm #

    My Karl Forester has grown very tall this summer and is almost too tall for front of house! Can I cut it back some so it looks a little neater. I’ve read that early spring is the best time to cut back. Will it hurt them if I cut them about 1/2 way down now. (oct. Michigan)

    • Catherine November 6, 2017 at 12:01 pm #

      Hi Mickey,

      Yes, you can go ahead and cut your Karl Foerster grass back in fall if you wish, either halfway or all the way. It won’t hurt it. It’s a matter of personal preference. In Colorado, we cut them back in February because they tend to look good all winter when everything else is dormant, but there’s not a biological reason. It is, however, important to cut them back before they start growing again in the spring.

  9. Mike November 3, 2017 at 12:59 pm #

    Hi Catherine. I bundle the tall seed heads and use them for blocking an area under the deck, stuffed into cinder blocks upright. Question is, can I cut them earlier in the fall, say November during our cleanup, and still expect them to rise to the occasion next spring? Can I cut the leaves to the ground at that time as well? Didn’t want to wait until February, when the snows at 6200′ may have broken down and bent the heads. Should I wait until February to cut the leaves down to the ground. Thanks!

    • Catherine November 6, 2017 at 11:55 am #

      Hi Mike,

      It’s fine to cut back your seedheads and leaves in November. The leaves might still be a little green at the base, but I wouldn’t expect any negative effects on your grasses the following spring. Karl Foerster grasses are quite hardy. Most places in Colorado we cut them back in February because they provide much-needed winter interest. Also, we tend to get grass-crushing snows only occasionally. But in terms of plant health, it’s fine to cut them back in late fall. Hope that helps!

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