Ornamental · Poaceae
Japanese Blood Grass
Imperata cylindrica 'Rubra'
Give it full sun and even moisture, and the blades blaze 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 wins gardeners over for one thing above all: color. Its slim upright blades launch out green at the base and deepen to blood-red from the tips down, and the whole clump seems to catch fire the moment low sun pours through it from behind. A true grass, it packs into a neat knee-high mound and grows slowly enough to hold its ground right where it goes in.
This hardy perennial shrugs off brutal cold, powering through winters down to -20°F (-29°C) and rocketing back from the roots every spring. Once it settles it barely asks for a thing, and it hits peak color in full sun with steady moisture. As an ornamental it steals the show at the front of a bed or against a darker backdrop that throws the red into sharp relief.
One trait lifts this plant clear of the ordinary ornamental, and it matters a great deal. The red cultivar can revert to its wild green form, cogongrass, a federal noxious weed and one of the most destructive invasive grasses anywhere. The plant itself stays harmless to people and pets, but the legal and invasive side is the real deal, and every bit of it lands below.
Care
The short version: full sun for the deepest red, soil kept evenly moist, and one solid cutback in late winter. Watch the clump for green shoots and rip them out the instant they appear.
Light
Plant it in full sun and the color pops like nothing else. The blades handle a touch of shade, but crank past light shade and the red slides toward green, which throws away the whole reason you grew it.
Water
Keep the soil evenly moist, splashing it about every 5 to 10 days as the weather calls for. A settled clump laughs off a short dry spell, but steady moisture unlocks the best color and the most vigor.
Soil
It thrives in fertile, well drained loam that holds a bit of moisture. A pH anywhere from 5.5 to 7.0 works, which sweeps in most ordinary garden ground.
Temperature
This is one tough, cold-hardy grass that powers through 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 blasts back from the roots each spring.
Humidity
Plain outdoor humidity is all it wants, so there is nothing to fiddle with here. It rolls with average garden air, no complaints.
Feeding
One hit of balanced general-purpose fertilizer in spring does the trick. Skip feeding through the rest of the season, since the grass cruises along at its own steady, moderate pace.
Pruning
Cut the whole clump to the ground in late winter, before new growth kicks off. The one job you cannot let slide is pulling any all-green shoots the second they surface, since they flag 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 jam the pot or the center starts dying out. Splitting it keeps the plant vigorous and the color firing.
Size & spacing
Count on a clump about 12 to 18 inches (30 to 46 cm) tall spreading 12 to 24 inches (30 to 60 cm) wide. Hand each plant that much room so the mound can fill out without crowding.
When to plant
Get Japanese blood grass in the ground in spring once the last frost clears, and it digs in over that first growing season. It rarely flowers in cultivation, so there is no bloom to hang around for. Cut the clump to the ground in late winter, and fresh red growth rockets 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 trouble with this grass boils down to two things: weak color, or the more serious business of the plant lunging back toward its invasive green parent. Learn to tell them apart fast, because one is a quick fix and the other demands you move right now. Match what you see below and pounce while it still counts.
Green blades shooting up from the red mound
Spot strong green shoots and you are watching the plant reverting to cogongrass, the wild green form of the species and one of the fiercest invasive grasses going. Jump on it: dig out every green shoot the moment it shows, rhizomes and all, then bag the lot and bin it. Keep it far from the compost, and swing back to check the spot often, because that green growth races along 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
Outlawed or noxious-weed listed in many states
Nail down the legal side before this grass goes anywhere, because the species ranks as a federal noxious weed, which makes selling it or hauling it across state lines flat-out illegal, and many states ban the ornamental form too. As cogongrass it throws up dense, fire-prone stands that steamroll native plants. Check your state's rules first, give the southeastern US a wide berth, and yank and destroy any plant growing where it does not belong.
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
Washed-out color nearly always traces straight back to too little sun. Full sun fires up the deepest blood-red, while a clump languishing in heavy shade clings to its green. Shift it into a brighter, sunnier spot, keep the soil evenly moist, and the color comes roaring back.
Fix:
- Relocate to a site with full sun for best red color
- Ensure soil stays evenly moist
Toxicity
Great news up front: Japanese blood grass is not poisonous to people or pets, and the ASPCA keeps it off its toxic-plant lists. A nosy cat or dog might cough up a little grass after a chew, and that is the whole of it. The real thing to keep tabs on is not poison at all but how fast it can turn invasive, so dig into the section above on reversion and state law.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Cats are perfectly fine around it. Chew a blade and a cat might bring up a little grass, but that is just what cats do with any plant, not poisoning.
Dogs None
Dogs get a clean pass here, with no toxins in play. A stray mouthful lands at nothing worse than a bit of mild, passing stomach upset.
Horses None
Horses are in the clear too, since this grass skips all the toxins that lurk in so many ornamentals.
Rabbits None
Rabbits can munch the blades to their heart's content, because nothing in the plant is toxic to them.
Livestock None
Cattle, goats, and sheep face zero poisoning risk from the foliage.
Birds None
Birds are safe around it, with nothing in the leaves or seed to poison them.
People None
It is safe to handle and safe to keep where kids play. Nobody grows it 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
Two forms are worth knowing here, and the gulf between them tells the entire story of this plant.
Red Baron
This is the ornamental star you actually plant, its slim upright blades blazing blood-red from the tips down and lighting up the instant the sun shines through them from behind.
Imperata cylindrica (species, cogongrass)
The plain green wild form is a federal noxious weed and one of the most destructive grasses on earth, hurling up dense fire-prone stands, and it is exactly what the red cultivar can crash back into.
How to propagate
This grass bulks up one way, by splitting the clump, and it is a breeze as long as you stay sharp for any green-reverting growth.
DivisionEasy
Spring · One growing season
Split the clump in spring and you have got your one reliable way to bulk this grass up, since the cultivar barely ever sets usable seed. Lift a settled clump, break it into sections, replant, and each piece roots in over a single growing season. Just chuck any division sporting green reverting growth instead of handing it along.
Myths
The red blood grass makes a totally safe, no-hassle plant to grow.
The non-toxic claim holds up nicely, since the red form really is safe for pets. But the story does not end there: it can revert to the aggressive green cogongrass, the species itself is a federal noxious weed, and loads of states ban or restrict its sale. The real danger is invasiveness and legality, not poison.