Ornamental · Poaceae
Feather Reed Grass
Calamagrostis × acutiflora
Plant it in full sun and feather reed grass stands tall and feathered from June clean through winter.
Full sun
Every 5–10 days
USDA 4–9
3–5 ft · 0.9–1.5 m
Overview
Feather reed grass is the upright grass you have seen lining driveways and standing guard at the back of a border. It is a sterile hybrid of two European grasses, and the most famous form, Karl Foerster, was named Perennial Plant of the Year in 2001. The clump sends up narrow green blades in spring and then throws tall flower stalks that feather out in early summer.
What sets it apart is the strict vertical habit. The stems shoot straight up and hold their line even after the plumes fade to wheat, so the plant keeps its shape long after softer grasses have flopped. It is a cool-season grass, which means it does its growing in the milder weather of spring and fall and can take a rest in the worst of the summer heat.
It asks very little once it settles in. Hardy from zone 4 to zone 9, it shrugs off heavy clay, cold winters, and damp ground that would rot other grasses. Leave the plumes standing through the cold months for winter structure, then cut the whole clump down before the new shoots push up in spring.
Care
The short version: full sun, average to moist soil, and not much fuss. Water it through a long dry spell, skip the heavy feeding so the stems stay upright, and cut the clump to the ground once a year in late winter.
Light
Give feather reed grass full sun for the straightest, strongest stems. It will take partial sun or light shade, but the more shade it gets, the more the stalks lean and flop and the fewer plumes it sends up.
Water
Once established it handles a lot, from dry banks to wet, heavy ground that drowns most grasses. It does best in fertile soil that never bakes bone dry, so water the clump through a long drought. Water every 5 to 10 days in a dry stretch, and otherwise let the weather do the work.
Soil
Almost any soil suits it. Well-drained fertile loam is ideal, but it copes with heavy clay, poor ground, and damp sites far better than other ornamental grasses, which is a big part of why gardeners reach for it.
Temperature
This is a tough, cold-hardy grass, comfortable from about -29°F to 100°F (-34°C to 38°C). The deep cold of zone 4 winters does not faze it, though it can sulk and brown a little during the worst of a hot, humid summer.
Humidity
Outdoor humidity is no concern, so there is no number to hit. What matters far more is air movement, since stagnant, muggy air in a crowded planting is what lets rust take hold on the leaves.
Feeding
Feed lightly in spring with a balanced fertilizer or a thin layer of compost, and stop there. Rich, overfed soil pushes soft growth that flops and ruins the upright shape you grew it for.
Pruning
There is just one cut a year. Shear the whole clump down to a few inches above the ground in late winter or very early spring, before the new green shoots break, and the plant fills back in within weeks.
Repotting
In the ground, the work is dividing rather than repotting. Every few years, when the center thins or the clump loses vigor, dig and split it in spring or fall, keep the healthy outer pieces, and throw out the dead middle.
Size & spacing
A clump reaches 3 to 5 feet (91 to 152 cm) tall in flower while staying narrow, with a spread of about 18 to 30 inches (46 to 76 cm). That tight footprint is why it works so well as a vertical accent or a row.
When to plant
Feather reed grass goes in the ground in spring or fall, while the soil is cool and the roots can settle without summer stress. The flower plumes rise in early summer, around June, and then hold on as tan spikes right through fall and into winter.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall
- Harvest: Early summer (June); plumes persist through fall and winter
Hardiness
USDA hardiness zones: 4–9
Temperature: down to -34°C
Troubleshooting
Most trouble with feather reed grass comes down to too much shade, too much summer heat, or an aging clump. The signs are easy to read once you know them. Match what you see below, then make the one change that fixes it.
Orange, powdery spots that rub off on your fingers
Those rusty pustules are rust disease, and they show up after long spells of rain or hot, wet weather. Strip off the badly marked leaves, open the planting up so air can move through it, and keep water off the foliage. Clear out any infected growth at the late-winter cutback so it doesn't carry over.
Fix:
- Improve air circulation and avoid overhead watering
- Remove and discard badly affected foliage
- Cut back and dispose of infected growth at the late-winter cleanup
A bare, dead patch opening up in the middle of the clump
An aging clump hollows out from the center while the outer ring keeps growing, and that is the plant asking to be split. Dig it up in spring or fall, replant the vigorous outer divisions, and toss the dead middle. Doing this every few years keeps it full.
Fix:
- Dig and divide the clump in spring or fall
- Replant healthy outer divisions and discard the dead center
Tired, browning foliage in the heat of mid-summer
This is a cool-season grass, so it does most of its growing in spring and fall and can stall when summer turns hot and muggy, especially in the South. Don't panic and cut it back. Water it through the worst of the heat and it greens up again on its own as the weather cools.
Fix:
- Water during prolonged heat and drought
- Tolerate the temporary summer decline; do not cut the whole plant back
- Site in full sun in cooler regions for best vigor
Stems leaning and flopping instead of standing tall
When the prized vertical shape goes soft, the culprit is almost always too much shade or too rich a soil. Move the clump into full sun and ease off the feeding. Lean conditions are exactly what keep the stalks ramrod straight.
Fix:
- Transplant to a full-sun location
- Reduce fertilization and avoid overly rich soil
Toxicity
This one is easy to live with. Feather reed grass is non-toxic and is not on the ASPCA poison lists, so it is safe around cats, dogs, and the rest of the household. The only real catch is physical: the blades and seed heads carry sharp edges that can scratch, and a pet that nibbles a mouthful of grass may bring it back up.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats Safe
Safe to be around. A cat that chews a blade may cough it back up the way it would any grass, but there is nothing poisonous in it.
Dogs Safe
No toxins here, so a dog can sniff and nibble without harm. The worst you might see is a little vomiting after a big mouthful of grass.
Horses Safe
Not listed as a problem for horses. Mind only the stiff, sharp blades, which can scratch on the way past.
Rabbits Safe
Nothing toxic for rabbits. The coarse, sharp-edged leaves are not much of a treat, so they tend to leave it alone anyway.
Livestock Safe
Cattle, goats, and sheep can graze near it without poisoning. It is grown for looks rather than forage, so they rarely bother with it.
Birds Safe
Harmless to birds, which often pick at the seed heads. Since the popular forms are sterile, there is little seed to find.
People Safe
No risk to people. Just wear gloves when you cut it back, because the leaf edges and seed spikes can nick bare skin.
Foliage and seed heads have sharp edges and points that can scratch; grass pollen may bother allergy sufferers, and pets that nibble grass may vomit, but it is not poisonous.
Varieties
A few named forms cover almost every feather reed grass you will meet at the garden center. These are the ones worth knowing by name.
Karl Foerster
The classic upright sterile hybrid that won Perennial Plant of the Year in 2001, carrying green blades and tan vertical plumes that never self-seed.
Overdam
A compact variegated form around 3 feet tall whose green leaves are edged in clean white stripes.
Avalanche
A variegated selection close to 4 feet tall, marked by a broad white stripe running down the center of each leaf.
Calamagrostis brachytricha (Korean feather reed grass)
A related warm-season cousin with a looser, arching mound and pinkish plumes that open in late summer and fall.
How to propagate
Because the popular forms are sterile, you multiply feather reed grass by splitting a clump rather than sowing seed. It is the same simple job that keeps an old plant young.
DivisionEasy
Spring or fall · One growing season
Division is the way to multiply feather reed grass, and it doubles as the cure for an old clump that has hollowed out in the middle. Dig and split an established plant in spring or fall, replant the healthy outer pieces, and they settle in over a single growing season.
SeedDemanding
Not applicable for sterile cultivars · Not applicable; sterile cultivars set little or no viable seed
Seed is a dead end for the cultivars most people grow. Sterile hybrids like Karl Foerster set little or no viable seed, so there is nothing to sow, and starting from seed simply is not practical for the named forms.
Myths
All ornamental grasses self-seed and take over the garden.
The popular forms of feather reed grass, Karl Foerster among them, are sterile and set little or no viable seed. That means they stay put and never sow themselves around, so the standard cultivars are well-behaved and non-invasive. The wild species and the odd seedling can spread, but the hybrids you buy will not.