Plant Profile: Karl Foerster grass

Karl Foerster grass as an informal screening plant.

Karl Foerster grass as an informal screening plant.

We highlighted Karl Foerster grass back in 2012 as one of our favorite plants for Minnesota, but let's sing the praises of this striking, easy care, four-season beauty once again.

Even in his 90s, Karl Foerster enjoyed time in his garden. (1967 photo)

Even in his 90s, Karl Foerster enjoyed time in his garden. (1967 photo)

Karl Foerster (Calamagrostis x acutiflora ‘Karl Foerster’) is a feather reed grass, an ornamental clump-forming grass that grows in USDA Zone 4 and southward. It is named for a German horticulturist and an early pioneer of lower maintenance gardening. Karl Foerster was born in Berlin in 1874 and lived and gardened until 1970! (More evidence of the health benefits of gardening!)

According to this interesting short biography, he was the father of the "new German style" garden, which emphasized plants that had beauty, resilience and endurance. In addition to his famous (some might say ubiquitous grass), he collected and bred delphiniums, white roses and was the first person to cultivate the very popular Rudbeckia fulgida var. sullivantii  ‘Goldsturm’.

Because it is clump-forming, Karl Foerster grass does not spread. It stays put in a nice, slowly expanding clump. After seven to 10 years, you may want to divide it. The plant has basically no disease or pest problems and requires little in the way of fertilizer or even water. In the driest of years, Karl Foerster stands tall.

This grass grows 3 to 4 feet high and looks lovely in the back of a planting bed or even used as a low screen. I have several planted around my front yard patio. The plants supply just enough cover to sit on the patio without feeling exposed. They look wonderful grown in masses and are the perfect companion to many prairie plants.

Hoar frost clings to the seed heads of Karl Foerster grass.

Hoar frost clings to the seed heads of Karl Foerster grass.

Each year, the Karl Foerster grass begins with simple green blades. In late summer, golden flower heads form, which wave in the breeze. While you can cut it back in fall, I like the way the grass looks in winter, too. Hoar frost clings prettily to the seed heads and the plant stands tall through most (not all) of the winter. Some plants will lodge (fall over), but many stay tall until spring. I usually cut mine back to about 6 inches tall in late April.

For a plant that requires almost no care, you cannot go wrong with Karl Foerster grass.

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  1. Cindy Marso on August 25, 2016 at 8:51 am

    My Karl Forester has what looks to be some kind of blight or fungus. The leaves have rust colored like lines on it. I looked up diseases and the miscantus blight best matched what is going on with mine. Now what?

  2. Mary Lahr Schier on August 26, 2016 at 11:11 am

    And, a bit more info from the National Gardening Association:

    ‘Karl Foerster’ is usually free of serious disease or insect problems although a foliar rust disease may appear in particularly wet summers and in situations with poor air circulation. Browsing deer don’t bother it. Little maintenance is required except to cut back the stems to about 6 inches in late winter or early spring. In areas with mild winters the foliage may remain evergreen.

  3. Chrs on July 4, 2018 at 2:32 am

    I have planted Karl forester grass in a very Sandy soil and they don’t appear to be growing. how fast do they grow maybe I am being anxious it had been abouta month and I can’t really see any growth they were about 14″ high and are the same

    • Mary Lahr Schier on July 4, 2018 at 3:06 pm

      Most perennials do not grow much their first year. I planted some Karl Foerster grass in very poor soil (somewhat sandy) between my patio and my neighbor’s patio. The first year it sat there, last year, it grew a bit taller but not what I had hoped for. This year, it is a full 5 feet tall and very lush. The old saying, first year sleep, second year creep, third year leap is true for many perennials. Good luck!

    • maurita on August 15, 2020 at 5:12 pm

      Karl Forester likes a lot of water and since your soil is sandy it’s not going to grow because the water will go right through it. My recommendation would to mix your soil with a good humus compost soil which can be found at any big box store.I also mix the soil 2-3 feet from the grass so the grass will have a good foundation to hold the water.You could put some type of water feature that would drip water continuous water. I have a bird bath with a dripper and it works great. Google what you can use to do what you to accomplish. I hope I helped. Happy gardening

  4. gina sanchez on May 15, 2019 at 1:46 am

    I got some transplants of Karl forester grass from a construction site(they were going to throw them away) when I got them the root ball was still moist, but the were a little wilted, I planted them in my yard and have been watering them but they look dead. Does it take a year or two for them to come back from the shock?

    • Mary Lahr Schier on May 15, 2019 at 3:10 am

      Where are you located? In the North, Karl Forster is just coming out of dormancy now. Don’t over-do the water. Ornamental grasses can usually take a bit of dryness. Good luck!

  5. Lucy Jarman on November 13, 2019 at 10:29 pm

    is this grass native to MN?

    • Mary Lahr Schier on November 13, 2019 at 10:43 pm

      Karl Foerster grass is a hybrid combining two species of Calamagrostis — one from Europe (where it was bred) and one from Asia. The genus Calamagrostis is widespread throughout the northern hemisphere. Twelve species are native to North America, including the most common one, C. canandensis. This is native from the Arctic Circle to Arkansas, including in Minnesota. Here’s an article from the USDA on that native feather reed grass.

      • Maureen Klaboe on October 25, 2021 at 3:32 am

        Hello, I have many KF grasses and have harvested the seed at the top of the plant to try my hand at growing them from seed. I need some direction on how best to do that. Would it be best to prepare the soil and plant now in the fall? Or should I store the seed and plant after the last frost in Montana in the spring?? Any advice is welcome. Thanks!

        • John Winterberg on March 21, 2022 at 3:19 am

          seeds are sterile; thereby, this grass will not self-seed and become an invasive problem. It also means that it cannot be propagated from seed.

  6. Kari Servais on April 20, 2020 at 7:10 pm

    I have several spots where I’ve planted Karl Foerster grass. I’ve noticed some older plants are bare in the middle, with the grasses growing around like a ring. My initial thought was perhaps an animal was using the center as a shelter and its just beat down. Another thought was that I wasn’t trimming enough in the spring and the older growth (3-6 in.) stalks which are almost like reeds have crowded the new growth. Any thoughts?

    • Mary Lahr Schier on April 20, 2020 at 7:57 pm

      It sounds like the clumps need to be divided. While you don’t have to do it often, you can divide Karl Foerster grass. Just dig up the clump this spring, then cut it into two of three pieces and replant them.

      • Paula Rudser-Stolba on August 15, 2020 at 3:46 am

        Thanks for the advise. I have the same problem, my clumps are 14 years old!

    • Paula Rudser-Stolba on August 15, 2020 at 3:46 am

      Same here, “dead” spots in the middle of the clumps, but our clumps are now 14 years old! Very Hardy. I am going to try thinning/dividing the clumps.

  7. Ashtyn Silva on May 8, 2020 at 11:34 pm

    Planning my landscaping in my new back yard! Advice is appreciated! Which is better for winter interest? (Minnesota, harsh winters, lots of snow.) I’m debating between red flame grass or Karl Foster. If anyone has alternative selections I would be appreciative. I would like to do pampas, because of the beautiful plumes, but I don’t have quite enough space. Thanks!!!

    • Mary Lahr Schier on May 11, 2020 at 1:35 pm

      I’m a fan of Karl Foerster, but any grass is wonderful in winter. (I like little bluestem, too.) The flame grass is slower to come up in spring, though, so give it time to green up each year if that’s what you choose.

  8. Jeff A. on May 26, 2020 at 1:07 am

    I’ve had to replant my KF grass a couple times now because it either dies or just barely comes back after winter. It’s planted on the SE and SW corners of my garage. So sun shouldn’t be an issue. It’s gets water when I water my lawn and everything around it (purple sand cherry, hydrangea, and tiger eyes) all thrive. The only thing I can think of that may cause an issue is the concrete garage slab is heated. That means the ground where the KF grows may not freeze over winter. Does the plant need the hard freeze to go dormant? Is it spending stored energy over winter instead of going dormant and then takes longer or can’t recover come spring?

    • Mary Lahr Schier on May 26, 2020 at 2:05 pm

      Jeff — I’m stumped. Karl Foerster is hardy down to Florida, so not freezing should not be a problem. My first thought was that maybe it was getting too much water, if you have a sprinkler system, but normally it does well around ponds. It may also be it’s struggling because it has been moved several times. I’d give it a year or two in that spot, and if it’s not working, consider replacing it with something else.

  9. Jodelle Ista on June 6, 2020 at 9:59 am

    My daughter bought some Karl Forester grass. It looks like regular lawn grass that has gone to seed. What should it look like in June?

    • Mary Lahr Schier on June 8, 2020 at 5:42 pm

      Jodelle — My Karl Foerster is between 2 and 3 feet tall now (June 8) and all green. It will grow a bit more and then send up the seed talks, which will bring the total height to around 5 feet by August. It does take a year or two to get established. My grouping is almost 4 years old.

  10. kcj on June 15, 2020 at 4:02 pm

    My KF has bent reeds so it looks floppy and far from upright. Will they straighten out or are they likely to struggle? Should I prune the bent ones? Thanks

    • Mary Lahr Schier on June 15, 2020 at 5:22 pm

      They won’t straighten up so you may want to cut them out. If the grass is floppy, it may need more sun or to be divided.

  11. Tony on July 5, 2020 at 4:28 pm

    My KF grass plants are thriving and full of seeds. The problem is they are going into our pool. Can I cut off their seed heads now in early summer without damaging the plants?

    • Mary Lahr Schier on July 7, 2020 at 6:54 pm

      Other than changing the looks, it should not damage the plant. You may want to consider re-siting the plants, because this will likely be an ongoing problem.

  12. Dave Bailey on July 6, 2020 at 9:28 pm

    My KF was planted in mid May this year. They are about 1.5 to 2 feet tall. If i straighten out the tallest grass blade, it is about 33″. My question is will the plants from a seed head in their first year. They are growing about 3+ inches per week at this point. I see you mention they will take a few years to mature, but I’m hoping i can expect some seed heads later this summer.

    • Mary Lahr Schier on July 7, 2020 at 6:53 pm

      I would expect they will form a seedhead this year. They sound very healthy!

  13. Judy Markham on July 22, 2020 at 3:03 pm

    I have a long row of KF next a driveway that I planted last year. At the start of the row they have grown to 5′ tall! At the end(where they get less sun) they are only about 4′. If I want a more uniform appearance, can I trim the taller ones a few inches? or will this hurt the plant this time of year?

  14. Annie B on July 28, 2020 at 11:21 am

    I am planning to put a border of Karl Forester along a walkway that is currently lined with sun-baked Hosta . The only thing that I do not love about Karl Foerster is that it has such an upright growth pattern. Would it be more branching/ weeping if I did not cut it back at all at the end of the season?

    • Mary Lahr Schier on July 28, 2020 at 1:49 pm

      No, the new growth would just come up through the old growth. If you want a more weeping habit, you could try little bluestem (there are a number of different cultivars available) or for a shorter grass, prairie dropseed. It has a lovely draping habit.

  15. Judy Markham on August 1, 2020 at 1:41 pm

    I have a long row of KF next a driveway that I planted last year. At the start of the row they have grown to 5′ tall! At the end(where they get less sun) they are only about 4′. If I want a more uniform appearance, can I trim the taller ones a few inches? or will this hurt the plant this time of year?

    • Mary Lahr Schier on August 3, 2020 at 5:46 pm

      You can trim them. It might be a bit hard now that most have set their flowers/seedheads. Good luck!

  16. Laura Wilt on September 3, 2020 at 5:49 pm

    When is the best time of year to transplant KF grasses?

    • Mary Lahr Schier on September 3, 2020 at 6:10 pm

      Early spring is your best bet.

  17. Allison on March 10, 2021 at 7:17 pm

    When buying this grass what size makes most sense to purchase? 1 gallon? 3 gallon? other? Thanks

    • Mary Lahr Schier on March 11, 2021 at 5:12 pm

      A 1 gallon plant is probably fine — these grasses will size up within a year or two.

  18. Sarah on June 3, 2021 at 12:04 am

    Hi there, I am not sure if what I have is Karl forster. It grows to about 5′ and has a beautiful, soft, tan colored plume. The reason I am not sure if it is KF is it has a very strong tap root system and has spread some in my garden. Any idea what this is? Thanks for your time!

  19. FRANK SCHENCK on August 25, 2021 at 12:14 pm

    About 2 years ago I brought several Karl Forrester grasses back with me from S. Dakota to my home in Biloxi, Ms. They have been in the ground for near that period of time. They have developed lush green foilage at the bottom, but have failed to put out the seed heads. We are zone 9. Any idea why not??

    • Mary Lahr Schier on August 31, 2021 at 2:24 am

      Your area is on the edge of Karl Foerster’s range. It may be its too warm for it to set seed properly.

  20. dennis Barta on September 24, 2021 at 3:30 am

    We went to the nursery to buy some KF. They have it in 2 gallon pots and the plants are 4 ft tall and quite thick with stems but the seed heads are mostly bare. We bought some last year and in their 1st year they produced nice seed heads. The clerk assured us next year these will produce the nice seed heads but we are concerned there might be something wrong. What do you think? Thanks

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