Chigaya: Why Japan Honours the Grass the World Calls Cogongrass
In the southern United States, cogongrass is one of the most feared weeds there is. In Japan, the same plant is called chigaya. Shrines weave it into large rings that people walk through to stay well, and an old Japanese word for rice dumplings comes from its leaves.
We are a small tree care and landscape business in Mie Prefecture, central Japan. We pull chigaya out of lawns and flower beds, and we also see it holding up the grassy banks along rice fields. This page is about one grass with two very different reputations.
Native in Japan, invasive abroad
Chigaya is Imperata cylindrica, a perennial grass. In Japan it grows wild from Hokkaido to Okinawa, on river banks, field edges, coastal sand and open ground. It is a native plant here. The National Museum of Nature and Science in Tokyo lists it at 30 to 80 centimetres tall, flowering from April to June.
Its white spikes are the easiest way to spot it. When a whole field of chigaya flowers, the ground turns white for a while.
Outside Asia the story changes. The Global Invasive Species Database, run by a specialist group of the IUCN, includes cogongrass in its list of 100 of the World's Worst Invasive Alien Species. It describes the plant as one of the top ten worst weeds in the world, because of its spreading rhizomes, drought tolerance and ability to recover after fire.
In the United States it is listed as a Federal Noxious Weed. The Missouri Botanical Garden explains that it arrived in the southeastern states in the early 1900s, partly by accident in packing material and partly on purpose as forage and for erosion control.
A grass for purification: the chinowa ring
In late June, many Japanese shrines set up a large ring of chigaya at the entrance. It is called chinowa, and chi is an old name for chigaya.
Visitors walk through the ring during Nagoshi no Harae, the summer purification held on 30 June, halfway through the year. Walking through it is said to keep illness away for the rest of the year.
The custom is linked to an old story recorded in a lost local chronicle of Bingo Province, now part of Hiroshima Prefecture. A god travelling at night asked for a place to stay. A poor man named Somin Shorai welcomed him. In return, the god told him to wear a small ring of chigaya to escape disease. Over the centuries, the small ring became the large one that people now walk through.
The word for rice dumplings
Chimaki are sticky rice dumplings wrapped in leaves, eaten in Japan around Children's Day on 5 May. Today they are usually wrapped in bamboo leaves or other leaves.
The Japanese encyclopedia Nipponica explains that the name comes from chi-maki, chigaya wrapping, because the rice cakes were once wrapped in chigaya leaves. The leaf changed. The name stayed.
A snack in a 1,300-year-old poem
Young flower spikes of chigaya, picked before they open, are called tsubana. They taste faintly sweet. The National Museum of Nature and Science notes that children once ate them as a snack.
They also appear in the Man'yoshu, Japan's oldest collection of poems, compiled in the 8th century. The museum counts 26 poems in it about chigaya. In one exchange, a poet named Ki no Iratsume sends tsubana she picked in the spring fields to the poet Otomo no Yakamochi, and tells him to eat them and put on some weight. He writes back that he has eaten them and only grows thinner, because he misses her.
The rhizome is used in Kampo, Japanese herbal medicine, under the name hakubokon.
Thatch, banks and fields
Japanese thatched roofs are called kayabuki, roofs of kaya. Kaya is not one plant. The Japan Thatching Culture Association explains that it is a general word for the grasses used on roofs. Japanese silver grass (susuki) is the most common. Reed, kariyasu and chigaya are among the others.
On farmland, chigaya often grows on the banks between rice fields. The museum notes that it forms grasslands on embankments, river banks and field ridges. In Japan, chigaya grassland on river banks has been kept in place by regular mowing and burning of the banks, and small wildflowers grew among it. Where taller grasses such as susuki move in, chigaya slowly gives way to them.
Japanese blood grass
Gardeners in the United States and Europe may know chigaya by another name: Japanese blood grass. It is sold as the cultivars 'Rubra' and 'Red Baron', with leaves that turn deep red.
In Japan, a red-leaved strain is called benichigaya and is grown in shallow pots for display. The museum also notes that ordinary chigaya has beautiful autumn colour.
The Global Invasive Species Database warns that the red forms can revert to the green, invasive type. Because cogongrass is a Federal Noxious Weed, a federal permit is needed to move it between states, and the University of Wisconsin notes that even the ornamental types are prohibited in most southern states. If you garden in North America, check your state's rules before planting it, and contact your local extension office if you see the green form spreading.
Chigaya in our clients' gardens
In Japan, even though it is a native plant, chigaya is not welcome in a lawn. Its white rhizomes run under the soil, and if you only cut the leaves, it comes back from what remains underground.
In one private garden in Komono, Mie, that we have looked after since 2020, chigaya was spreading through the lawn. From May 2021 we pulled it out by the roots at our regular visits. By September 2022 it had almost stopped coming up, and by the end of that year other, broad-leaved weeds were appearing in its place instead.
It took about a year and a half of steady work. Chigaya does well in poor, sunny ground. When it starts to give way to other plants, we take that as a sign the soil and the garden are changing.
Common questions
Is chigaya the same plant as cogongrass? Yes. Both names refer to Imperata cylindrica. Plants in Japan are often treated as the variety koenigii.
Is it an invasive species in Japan? No. It is native to Japan and has grown here for a very long time. It is invasive in the United States and many other places where it was introduced.
Can you eat chigaya? Young spikes were once eaten in Japan as a children's snack. We do not recommend eating plants from roadsides or treated ground.
Is Japanese blood grass safe to plant? It depends on where you live. Its red forms can revert to the invasive green type, and in the United States it is regulated. Check local rules first.
One grass, two stories
Where chigaya is native, people have lived with it for centuries. They made purification rings from it, named a food after it, wrote poems about it and used it on their roofs.
Where it arrived as a stranger, it became one of the hardest weeds to control. The plant did not change. Its relationship with the people and the land around it did.
