Ornamental · Poaceae
Japanese Blood Grass
Imperata cylindrica 'Rubra'
Give it full sun and even moisture, and watch the blades light up blood-red from the tips downward.
Full sun
Every 5–10 days
USDA 5–9
12–18 in · 30–46 cm
Overview
Japanese blood grass is grown for one reason more than any other, and that is its color. The narrow upright blades begin green near the base and warm to a deep blood-red from the tips down, and the whole clump seems to catch light when the low sun passes through it from behind. A member of the grass family, it settles into a neat mound around knee height and grows slowly enough to stay right where you plant it.
You are working with a tough perennial that laughs off real cold, coming through winters as low as -20°F (-29°C) and returning from its roots each spring. Once it has settled in, it asks very little of you, keeping its best color in full sun with steady moisture. As an ornamental it shines at the front of a bed or set against a darker backdrop that makes the red pop.
One trait sets this plant apart from an everyday ornamental, and it is worth understanding. The red cultivar can revert to its wild green form, cogongrass, a federal noxious weed and one of the most damaging invasive grasses anywhere. The plant is completely harmless to you and your pets, but the legal and invasive side is genuine, and it is all covered below.
Care
The short version: full sun for the deepest red, soil kept evenly moist, and a gentle cutback in late winter. Keep an eye on the clump for any green shoots and pull them out as soon as they show up.
Light
Give it full sun and you will get the richest color. The blades will take a touch of shade, but go any deeper than light shade and the red slips toward green, which rather misses the whole reason you planted it.
Water
Aim to keep the soil evenly moist, giving it a good drink about every 5 to 10 days as the weather dictates. A settled clump copes fine with a short dry patch, though steady moisture rewards you with the best color and the strongest growth.
Soil
It is happiest in fertile, well drained loam that holds a little moisture. A pH anywhere between 5.5 to 7.0 suits it nicely, which takes in most ordinary garden soil, so you rarely need to fuss.
Temperature
This is a genuinely hardy grass that handles a wide swing, from a deep winter low of -20°F (-29°C) to summer heat near 100°F (38°C). It dies back over winter and comes cheerfully back from the roots each spring.
Humidity
Everyday outdoor humidity is all it wants, so there is nothing for you to manage on that front. It takes average garden air in its stride without any complaint.
Feeding
One feed of balanced general-purpose fertilizer in spring is all it needs. There is no reason to keep feeding through the season, since the grass grows along at its own steady, moderate pace.
Pruning
Cut the whole clump down to the ground in late winter, before new growth begins. The one habit worth keeping is pulling out any all-green shoots the moment you notice them, because they signal a reversion to the invasive form.
Repotting
If you keep it in a container, divide and freshen the clump every 2 to 3 years, or sooner if the roots crowd the pot or the middle begins to fade. Splitting it keeps the plant lively and the color glowing.
Size & spacing
Look for a clump around 12 to 18 inches (30 to 46 cm) tall spreading 12 to 24 inches (30 to 60 cm) across. Leave each plant that much elbow room so the mound can fill out happily without crowding.
When to plant
Plant Japanese blood grass outdoors in spring once the last frost is behind you, and it will settle in over that first growing season. It rarely flowers in cultivation, so there is no bloom to wait around for. Cut the clump right down to the ground in late winter, and fresh red growth will push 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 troubles this grass is either faded color or, more seriously, the plant trying to slip back into its invasive green parent. It helps to tell the two apart, because one is a quick and easy fix while the other asks you to move fast. Match what you see to the notes below and respond while it still counts, and you will keep things well in hand.
Green shoots surfacing within the red mound
Take a breath, then act, because those strong green shoots mean the plant is reverting to cogongrass, the wild green form and a fierce invasive grass. Ease out every green shoot as soon as you spot it, roots and rhizomes together, then bag the pieces and put them in the bin. You have got this, just keep an eye on the same patch afterward, since underground growth can travel, and never toss it on the compost.
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
It may be outlawed or restricted in your state
This one is worth knowing before you plant, and it is nothing to panic over. The species counts as a federal noxious weed, so selling it or carrying it across state lines is not allowed, and plenty of states have banned even the ornamental form. In its green cogongrass shape it makes thick, fire-prone stands that push out native plants, so please check your own state's rules first, steer clear of the southeastern US, and gently remove and destroy any plant where it is not welcome.
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
If the red looks pale, do not worry, it is almost always just too little sun and easily fixed. Full sun brings out that gorgeous blood-red, while a clump sitting in deep shade tends to stay green. Move it somewhere brighter and sunnier, keep the soil evenly moist, and the rich color will find its way back.
Fix:
- Relocate to a site with full sun for best red color
- Ensure soil stays evenly moist
Toxicity
Here is the reassuring part: Japanese blood grass is not poisonous to people or pets, and the ASPCA does not include it among toxic plants. A curious cat or dog may bring up a little grass after a nibble, and that is all. The real thing to mind with this plant is not poison at all but how readily it can turn invasive, so do read the section above on reversion and state law.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
You can relax around cats. If one chews a blade and brings up a bit of grass, that is the ordinary response to any plant, not a sign of poisoning.
Dogs None
Nothing here will harm a dog. The worst a curious mouthful is likely to cause is some mild tummy upset that soon passes.
Horses None
Horses are in the clear, since this grass holds none of the toxins that trouble them in so many other ornamentals.
Rabbits None
Rabbits are welcome to nibble, because there is nothing toxic in the plant for them to worry about.
Livestock None
Cattle, goats, and sheep have nothing to fear from the leaves, which pose no poisoning risk at all.
Birds None
Birds are perfectly fine near it, with no poison lurking in the leaves or the seed.
People None
It is safe to handle and to keep where children play. Nobody grows it to eat, and the only thing to keep in mind is the pollen, which may bother 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 just two forms worth knowing, and the difference between them tells you almost everything about this plant.
Red Baron
This is the familiar ornamental you will bring home, its slim upright blades coloring blood-red from the tips downward and seeming to glow when 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 planet's most damaging grasses, forming thick fire-prone stands, and it is the shape the pretty red cultivar can quietly slide back into.
How to propagate
You have one simple way to make more of this grass, by dividing the clump, and it is an easy job as long as you keep watch for any green-reverting growth.
DivisionEasy
Spring · One growing season
Splitting the clump in spring is your one route to more plants, since this cultivar hardly ever sets seed you can use, and it is a friendly job. Lift a settled clump, tease it into sections, and replant them, and each piece will find its feet over a single growing season. Just be sure to discard any division showing green reverting growth rather than sharing it on.
Myths
That cheerful red grass is completely harmless and asks for no fuss at all.
The reassuring part is true, since the red form really is non-toxic to pets. What you do need to keep an eye on is that it can turn back into the aggressive green cogongrass, the species itself is a federal noxious weed, and many states ban or restrict its sale. The trouble here is invasiveness and legality, not poison.