Ornamental · Poaceae
Japanese Blood Grass
Imperata cylindrica 'Rubra'
Give it full sun and even moisture, and the blades light up blood-red from the tips down.
Full sun
Every 5–10 days
USDA 5–9
12–18 in · 30–46 cm
Overview
Japanese blood grass is grown for one thing above all: color. The slender upright blades start green at the base and turn a deep blood-red from the tips down, and the whole clump seems to glow when the low sun shines through it from behind. It belongs to the grass family and forms a tidy mound about knee-high, slow enough to stay where you put it.
This is a hardy perennial that takes real cold, surviving winters down to -20°F (-29°C) and coming back from the roots each spring. It asks for little once settled, holding its color best in full sun and steady moisture. As an ornamental it earns its place at the front of a bed or against a darker backdrop that sets off the red.
One thing sets this plant apart from a normal ornamental, and it matters. The red cultivar can revert to its wild green form, cogongrass, which is a federal noxious weed and one of the most destructive invasive grasses anywhere. The plant itself is harmless to people and pets, but the legal and invasive side is real and is covered below.
Care
The short version: full sun for the deepest red, soil kept evenly moist, and a yearly cutback in late winter. Watch the clump for any green shoots and pull them out the moment they appear.
Light
Plant it in full sun for the strongest color. The blades hold a little shade, but anything heavier than light shade and the red fades toward green, which defeats the point of growing it.
Water
Keep the soil evenly moist, watering it down roughly every 5 to 10 days depending on the weather. An established clump shrugs off a brief dry spell, but steady moisture gives you the best color and the most vigor.
Soil
It does best in fertile, well drained loam that holds some moisture. A pH anywhere from 5.5 to 7.0 suits it, which covers most ordinary garden ground.
Temperature
This is a tough, cold-hardy grass that takes a wide range, from a deep winter low of -20°F (-29°C) up to summer highs around 100°F (38°C). It dies back in winter and returns from the roots each spring.
Humidity
Ordinary outdoor humidity is all it needs, so there's no level to manage. It handles average garden air without complaint.
Feeding
A single feed of balanced general-purpose fertilizer in spring is plenty. There's no need to keep feeding through the season, since the grass grows at a steady, moderate pace on its own.
Pruning
Cut the whole clump down to the ground in late winter, before the new growth starts. The one job to stay on top of is removing any all-green shoots the instant they appear, because they mark a reversion to the invasive form.
Repotting
In a container, divide and refresh the clump every 2 to 3 years, or sooner if the roots fill the pot or the middle starts to die out. Splitting it keeps the plant vigorous and the color strong.
Size & spacing
Expect a clump about 12 to 18 inches (30 to 46 cm) tall that spreads 12 to 24 inches (30 to 60 cm) wide. Give each plant that much room so the mound can fill out without crowding.
When to plant
Set Japanese blood grass out in spring once the last frost has passed, and it settles in over the first growing season. It rarely flowers in cultivation, so there's no bloom to wait on. Cut the clump to the ground in late winter, and fresh red growth pushes up as the weather warms.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring after last frost
- Harvest: rarely flowers in cultivation
Hardiness
USDA hardiness zones: 5–9
Temperature: down to -29°C
Troubleshooting
Most of what goes wrong with this grass is either weak color or, more seriously, the plant trying to turn back into its invasive green parent. Learn to tell the two apart, because one is a quick fix and the other needs you to act fast. Match what you see below and respond while it still matters.
Green blades pushing up through the red clump
Those vigorous green shoots are the plant reverting to cogongrass, the wild green form of the species and one of the worst invasive grasses anywhere. Dig out every reverting shoot the moment you see it, rhizomes and all, then bag the material and bin it. Never compost it, and keep checking the spot, because green growth spreads fast underground.
Fix:
- Dig out the green-reverting shoots immediately, including rhizomes
- Bag and destroy all removed material; do not compost
- Monitor the area repeatedly for regrowth
The plant is banned or listed as a noxious weed where you live
The species is a federal noxious weed, so it is illegal to sell or carry across state lines, and many states ban the ornamental form outright. As cogongrass it builds dense, fire-prone stands that crowd out everything native. Check your state's rules before you plant or move it, stay well clear of the southeastern US, and pull and destroy any plant where it isn't allowed.
Fix:
- Verify local and state legality before planting or moving the plant
- Do not plant in or near the southeastern US
- Remove and destroy plants where prohibited
Washed-out color instead of deep red
Weak color almost always means too little sun. The blades turn the deepest blood-red in full sun, while a clump stuck in heavy shade stays mostly green. Move it to a brighter, sunnier spot and keep the soil evenly moist, and the color comes back.
Fix:
- Relocate to a site with full sun for best red color
- Ensure soil stays evenly moist
Toxicity
Good news on the toxicity front: Japanese blood grass is not poisonous to people or pets, and the ASPCA does not list it among toxic plants. A curious cat or dog might bring up a little grass after a chew, but that's it. The genuine risk with this plant is not poison at all, it's how easily it can turn invasive, so read the section above on reversion and state law.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe to be around. A cat that chews on the blades might bring up a little grass, but that's the usual reaction to any plant, not poisoning.
Dogs None
No toxins to worry about here. The most a dog is likely to get from a mouthful is mild, passing stomach upset.
Horses None
Not poisonous to horses, and it carries none of the toxins found in many ornamentals.
Rabbits None
Rabbits can nibble the grass without harm, since none of it is toxic.
Livestock None
Cattle, goats, and sheep face no poisoning from the foliage.
Birds None
Harmless to birds, with nothing in the leaves or seed to cause poisoning.
People None
Not poisonous to handle or to have around children. The grass isn't grown to eat, and the only thing to watch is pollen for anyone prone to hay fever.
Not chemically poisonous; pets that nibble grass may vomit or have mild stomach upset, and grass pollen can affect allergy-prone individuals. The real risk with this plant is invasiveness and legality, not toxicity.
Varieties
There are really only two forms worth knowing here, and the difference between them is the whole story of this plant.
Red Baron
The standard ornamental form, with upright slender blades that turn blood-red from the tips down and seem to catch fire when the sun shines through them from behind.
Imperata cylindrica (species, cogongrass)
The all-green wild form is a federal noxious weed and one of the worst invasive grasses on earth, building dense fire-prone stands, and the red cultivar can slip back into it.
How to propagate
This grass is multiplied one way, by splitting the clump, and the job is easy as long as you stay alert for any green-reverting growth.
DivisionEasy
Spring · One growing season
Division in spring is the only way to multiply this grass, since the cultivar rarely sets viable seed. Lift an established clump, split it into sections, and replant, and each piece settles in over a single growing season. Throw away any division that shows green reverting growth rather than passing it along.
Myths
The red ornamental Japanese blood grass is completely safe and trouble-free.
The red form is genuinely non-toxic to pets, so that part holds up. But it can revert to the aggressive green cogongrass, the species itself is a federal noxious weed, and it is banned or restricted for sale in many states. The real danger is invasiveness and legality, not poison.