How to Plant, Grow, and Care for Karl Foerster Grass
Are you looking for a beautiful ornamental grass for your garden? In this article, gardening expert Jason White tells you all about planting and caring for popular landscape workhorse 'Karl Foerster' Grass.
Ornamental grasses add elegance and interest to any landscape. They’re perfect for filling narrow spaces, creating privacy hedges, and adding a unique texture to your space. ‘Karl Foerster’ grass is popular since it doesn’t require much maintenance and can survive in wet areas where many plants can’t.
Though this grass doesn’t need much attention, you still need to know what it needs to thrive. It can tolerate less-than-ideal conditions, but too much of what it doesn’t need will cause it to flop over and eventually die. It’s relatively pest and disease-free, so you won’t have to babysit it much.
Let’s dive into this ornamental grass to learn what it needs to grow in your garden. You can count on this perennial grass to provide interest in your yard all year.
Plant Type Ornamental grass
Family Poaceae (grass family)
Species Calamagrostis x acutiflora
Native Area Europe
Exposure Full sun
Height 5 feet
Watering Requirements Medium to wet
Pests & Diseases Rust
Soil Type Sandy, loamy, clay
Hardiness Zone 4-9
Calamagrostis x acutiflora ‘Karl Foerster’ is a hybrid species of feather reed grass. It’s a cross between C. arundinacea and C. epigejos. Horticulturists purposely breed many hybrid plants, but this popular grass developed through natural cross-pollination throughout parts of Europe.
Karl Foerster, a German horticulturist known as the father of the “new German style,” discovered the plant. He specializes in landscapes full of beautiful yet resilient plants.
He discovered it during the 1930s, but the new grass variety didn’t enter the commercial realm until the 1950s. The US didn’t get this grass until 1964 when it was brought from Denmark.
This variety is similar to another cultivar of feather reed grass, Calamagrostis x acutiflora ‘Stricta.’ Plant nurseries may confuse the two, so know what you want before purchasing. ‘Stricta’ is self-seeding, but as a hybrid cultivar, ‘Karl’ produces sterile seeds.
This perennial grass grows in clumps. It’s a self-contained plant since it won’t spread beyond its clump. Clumps can become quite large, reaching up to three feet, but it won’t go beyond its maximum width.
This ornamental grass adds interest to the garden all year long. The bright green foliage and pinkish-purple plumes give off a feathery look all summer. It starts blooming in early summer, earlier than other feather reed grass cultivars.
In fall, ‘Karl Foerster’ turns a golden tan color. The afternoon sun will make it seem like it’s glowing, giving it beauty even when it’s dormant.
The foliage is typically five feet tall but can be a little shorter or longer, depending on its conditions. It will flop over when wet but perk up when it dries out. It will also flop when it’s time to divide the clump.
‘Karl Foerster’ can be paired with shrubs to create a hedge or privacy screen, or it can be used as a central or statement plant that stands out distinctively in the garden. You can use it to fill up empty, narrow spaces in your landscape or plant several together to create a beautiful “sea” of rustling feathery grass when the wind blows. They’ll look beautiful almost anywhere but work well along pathways or at the back of flower beds.
The grass can be used in floral arrangements, whether dry or fresh. If you want to keep the golden color and feathery look, harvest them before the flowers mature. You can also harvest the grass before they develop flowers, but remember that the spiky foliage may be a bit painful.
Since this grass doesn’t produce viable seeds, you only need to know how to transplant it. Whether you divide it from a mature plant or buy a nursery seedling, you can follow the same steps.
Plant your grass in early spring once all danger of frost has passed. The grass will need the entire growing season to get established in your yard to ensure it will survive winter. Once established, it’s a hardy plant, so giving it time to acclimate is important.
Dig a hole as deep as the root ball or nursery container and about twice as wide. Add fertilizer or compost to the soil if amending is necessary. Place the plant in the hole and backfill it with soil. The crown of the root ball should be above the soil line since the clumps are above ground.
After backfilling the hole, water the plant well. This will give it a good drink to help it establish, but it will also help the soil settle. Fill in low spots with soil and repeat the process as necessary.
Water your plant every few days for the first six weeks since new roots take about that long to develop. After six weeks, you can decrease the frequency to once a week.
If you want to plant en masse or in rows, space the plants at least 36 inches apart. This will allow the plants some room to develop clumps without stunting each other. If you want larger clumps that don’t need to be divided as much, leave up to 60 inches of space between the plants.
Ornamental grasses work well in containers. Planting them isn’t much different than planting them in the ground. There are only a few things you need to do a bit differently.
The plant should have room to grow, so ensure the container is deeper and wider than the root ball. The hole you’d dig for the plant should be twice as wide. Make sure your container can accommodate this size, or go even bigger to delay the need to repot later.
Since you won’t have existing soil to backfill the pot with, you’ll need to purchase some. ‘Karl Foerster’ grass is tolerant of several kinds of soil; sandy, loamy, and clay will all work well. Add compost or choose a soil full of nutrients so you won’t have to fertilize it the first year.
Fill the container with enough soil to make the plant the appropriate height. Just as the root ball needs to be slightly above the ground, it should be slightly above the soil line when container planting. Place the plant in the container and fill it up with soil. Water it well and fill in areas where the soil settled.
Even though this ornamental grass likes moist and wet conditions, the container should still have a drainage hole. It will ensure you’re not overwatering your plant and prevent water from collecting and becoming stagnant.
Container plants will also need to be divided periodically. Every three years is standard, but you may need to do it sooner, depending on the container size. The plant will eventually die in the middle when the clump gets too big, so repotting it into a bigger container won’t fix it. It’s better to divide the plant.
How to Grow
‘Karl Foerster’ isn’t a picky plant. It does well in wet soil, tolerates many soil types, and doesn’t require much maintenance.
This ornamental grass is a sun-loving plant that does well with plenty of sunshine. It will benefit from afternoon shade in hot climates when the heat is at its peak. The heat break will benefit the plant and help it bloom beautifully.
Too much shade will hurt the plant, though. Like other ornamental grasses, this one will flop over when it’s unhappy in excessive shade. The shade will also affect its growth and flowering, resulting in a disappointing plant. The “floppage” could become a tripping hazard if the plant is next to walkways.
Give this grass water and lots of it! It needs moist soil to survive and is quite tolerant of wet conditions. If you have a puddle-prone area that can’t grow anything, try putting this grass there. The thirsty plant will drink the water and tolerate any puddling that occurs.
The amount of water the plant needs each week will depend on several factors, like how much sun it receives, what kind of soil it’s planted in, and how much water drains from the soil. Well-draining sandy soil must be watered more often than heavy clay soil since the former won’t hold moisture for long.
You’ll likely need to water once each week at the bare minimum. However, you can skip watering if it rains. Established plants can handle drought better than newly transplanted plants. However, you’ll still need to provide them with supplemental irrigation during dry periods or if the storm doesn’t provide enough water.
This variety thrives in nutrient-rich soil that stays consistently moist. Loamy soils are ideal since they allow water to drain easily while retaining plenty of moisture, but the grass also grows well in sandy or clay soils. They don’t need any fertilizer if the soil has enough nutrients, so investing in good soil upfront is worthwhile.
The grass tolerates many conditions that are typically bad for other plants, making them good “last effort” plants for difficult areas. They can tolerate puddling to the point of light flooding and brackish soil, which is mildly salty.
You may only need to fertilize your grass if the soil is depleted of nutrients. Start new plants with a generous serving of compost and other organic matter to give them the nutrients they need for the year. Healthy soil won’t need fertilizer.
You can fertilize your plants once in early spring with a slow-release fertilizer. Feed the plants when new growth first appears. Use a balanced fertilizer, such as something with an NPK of 10-10-10. The grass isn’t a heavy feeder, so you shouldn’t need to fertilize again until next spring. You can also use compost once a year instead of fertilizer if you’d like to do so.
This is a low-maintenance plant that’s super easy to care for. You will have to tend to it a bit, but it will only be about once a year, and it’s not labor-intensive.
Ornamental grasses benefit from being cut back yearly to promote new growth and eliminate dead growth. Cut your grasses back to six inches tall once a year in late winter when spring is right around the corner.
Cutting the plant back will make it look neater and grow bushier. You technically don’t have to cut it back if you don’t want to, but it will look neater and grow better if you do.
You’ll need to divide the clumps periodically, usually every three years or so, but you can do it sooner or later based on your plant’s growth. Dividing the clumps will help your plants stay healthy and continue growing.
If you want more grass in your garden or to gift some to a friend, division time is the time to do it. Large clumps can be turned into several small clumps, and after a few years, those will turn into even more.
Dividing clumps is the only way to propagate ‘Karl Foerster.’ Even though the plant produces seeds, the seeds aren’t viable and won’t produce any seedlings. You might appreciate that if you don’t want it to spread! Buy plant starts at the nursery or get a clump from another gardener to get the plant started in your garden. Once it has established and grown, you can supply your own grass moving forward.
This variety is a hybrid between two species. Hybrid plants don’t produce true seeds, meaning they may not be like their parent plants. So, even if this grass produced viable seeds, you still wouldn’t get what you hoped.
The best time of year to divide grass clumps is in late summer or early fall. This will allow your separated clumps enough time to settle and establish just enough to get through winter.
Clumps probably won’t need to be divided for at least three years. Sometimes, you can wait up to a decade, but the plant might not look its best, depending on its condition. When clumps get too big, they die in the middle, and the plant will look unkempt. You won’t need to stress about dividing the clumps unless you see signs of stress in your plants.
You’ll need a sharp tool like a shovel or a Hori-Hori knife to divide ornamental grass clumps. The bigger the clump, the harder it will be to divide, so try to choose a tool that matches the plant’s size. A smaller tool is sufficient if you’re turning a large clump into several smaller ones.
Start by cutting the foliage back to six inches tall. The spiky foliage can be painful, so reducing it will help you. Dig up the entire clump from the ground, ensuring most roots stay intact. Damaging too many roots will cause new clumps to die.
Feel your way through the soil to find the root ball and pull dirt away from the roots. You can use your hands or a tool to do this. Once you have most of the soil pulled away, you should easily be able to lift the clump out of the ground with minimal root damage.
Once the clump is freed from the ground, you can divide it. Remove dead and diseased portions from the living portions. Since you’re doing this in late summer or early fall before the plant goes dormant over the winter, you can tell which parts are living and which died.
After removing dead portions, divide the living parts into clumps. You can make them whatever size you’d like, but a minimum of eight inches will ensure you have plenty of healthy roots to establish the new plant. Ensure every new clump has large roots, or the chances of surviving will decrease.
Divide with sharp tools by cutting through the clump like a cake or steak. Large clumps will be more difficult. Start on the edges and work your way through; carefully pull pieces apart as you can.
You can plant as described earlier once you’ve finished dividing the clumps. The clumps should be established when winter arrives and will begin growing larger the following year.
This ornamental grass has few problems, making it easy to care for. The main issue you may have with it is improper moisture. They thrive in moist soils and even do well in wet soil, so drying out could lead to plant stress. Flopping over or crispy foliage ends indicate the plant needs more water.
If the grass is dying in the center of a clump, it’s time to divide. Break it up into several smaller pieces and discard the dead portions.
The grass prefers full sun. Too much shade can cause the grass to flop over or bloom less. Relocate the plant for best results.
This type of grass isn’t known to have any major pest problems. What a relief! You should still monitor it to see if any pests of nearby plants have ventured over to try out your grass. Remove any pests by hand or spray them with neem oil or insecticidal soap.
This garden-friendly grass is known for being disease-free, too. However, you may spot some rust after consistent rain. Rust is a fungal disease that can’t be cured, so you’ll need to remove the infected portions of the plant to prevent it from spreading. You can prevent it by spraying fungicide in early spring before the disease appears.
The first case of anthracnose, another fungal disease, was reported in July 2005 in New Jersey. Though largely perceived as a generally healthy plant, you’ll still need to watch out for the occasional rogue disease.
Frequently Asked Questions
Q: Does ‘Karl Foerster’ grass attract animals?
A: The plant isn’t too attractive to animals and is often compelling to gardeners because they’re deer resistant. However, birds may be attracted to it when they seek shelter during winter.
Q: What are the benefits of this variety?
A: It’s a good plant for areas that don’t host other plants well due to too much moisture. They like moist soil and are tolerant of puddles and light flooding. They have few pest and disease problems, making them a great plant for new or hands-off gardeners who don’t want a hard-to-please plant.
Q: Is it invasive?
A: Thanks to its sterile seeds and clumping habits, it’s not invasive. It will drop seeds but never sprout, and the clumps don’t spread to create new clumps. It’s the perfect grass to fill a space with because it won’t get out of hand.
‘Karl Foerster’ grass is easy to please, making it a delight to have in the garden. With few pests and diseases, you won’t have to babysit this plant much; you’ll only need to worry about dividing it when it reaches its maximum size. It looks beautiful on its own, planted in groups, or beside other plants in a flower bed. If you’re new to ornamental gardening, this would be the plant to start with.