Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Ornamental grasses lend interest to your garden with their lovely seed heads in the fall and winter. Japanese blood grass provides interest year round with its bright red leaves.
What is Japanese Blood Grass?
Japanese blood grass (Imperata cylindrica) is a cultivar of a grass known as cogon grass, that is native to Southeast Asia. Cogon grass is highly flammable, contributing to many wild fires. The chemicals in the grass cause the fires to burn hotter than normal, killing the surrounding trees and vegetation. The blades of the grass burn but the rhizome from which they grow is able to survive the heat of the fire and grow back afterwards. This allows it to spread and colonize burned or disturbed areas, replacing the original plants.
Cogon grass spreads through the dispersal of its seeds by the wind and by expansion of its rhizome. Tilling will not kill the rhizome. Even the smallest piece will easily regrow.
Cogon grass is considered an invasive species in areas where it has been introduced. It forms thick mats which crowd out native species.
It was introduced to the US in the early 1900s both as packing material and as forage for animals, as well as for erosion control. It is now classified as a Federal Noxious Weed which means that growers need a permit if they want to transport it across state lines.
This grass has some positive uses. It has been used to prevent erosion and also to stabilize beaches.
The cultivars of cogon grass that are used in gardens have red leaves and are less invasive. Their seeds are sterile and the rhizomes spread more slowly. Readily available cultivars include ‘Red Baron’ and ‘Rubra’
Japanese blood grass is hardy in zones 5 – 9. It grows 2 – 4 feet high and 2 – 4 feet wide. The leaves start out green with a little red at the tip. As the season progresses, the red color spreads down the leaves. By the end of the summer, the leaves are all red except for some green at the base.
All of the red cultivars can suddenly revert to all green. When they do, they also take on their parents’ aggressive tendencies to spread and take over. If your red grass becomes green, destroy it immediately before it starts to spread.
The red cultivars rarely flower. When they do, the bloom period is March – May in temperate areas, and year round in tropical areas. The flowers grow on a round spike that grows to 16 inches tall.
How to Grow Japanese Blood Grass
Japanese blood grass can only be purchased as plants. It cannot be grown from seed because the cultivars that are available produce seed that is sterile.
For the brightest color, plant your grass in a sunny spot in your garden. It will grow in partial shade, but the red will not be as intense. It is not fussy about soil. A pH of 6.5 -7.5 is optimal. Japanese blood grass grows best in moist well-drained soil.
This grass is drought tolerant. There is no need for regular watering once it becomes established. During prolonged periods of drought, you will want to provide supplemental watering to prevent the leaves from turning brown.
Japanese blood grass grows in poor soils. There is no need for fertilizer. In fact, fertilizing it will cause it to start growing and spreading aggressively, taking over your garden.
How to Prune Japanese Blood Grass
Japanese blood grass is a cool season grass which means that it grows most actively in the cool weather of spring and fall.
It does not die back in the fall. It remains semi-evergreen during the cold winter weather, so it provides winter interest in your garden. Wait until spring when the plant starts actively growing again before cutting down last year’s foliage. You can either cut it down to the ground or only cut down any leaves that died over the winter.
How to Divide Japanese Blood Grass
You will need to keep an eye on this grass to make sure that it is not spreading into unwanted places in your garden. It can easily be divided to keep it small enough to not overwhelm the other plants.
Division can be done in either the spring or the fall. Use a garden spade with a sharp edge to cut the clumps into pieces that can be dug out of the soil. Don’t worry about your divisions being too small. This tough grass will readily regrow from even the smallest division.
Replant your divisions in another location and water well to help them settle in to their new home.
© 2020 Caren White
Caren White (author) on December 24, 2020:
It gives a big pop of color.
Peggy Woods from Houston, Texas on December 24, 2020:
That colorful grass would surely make for interesting accent pieces in a garden.