Turn over the edge of a field with a spade after the fall harvest, and you'll pull up long runs of white, jointed rhizomes. Knock off the soil and chew a piece, and a subtle sweetness comes through. This is the root of cogon grass (Imperata cylindrica), which covers sunny banks with white, silky plumes every spring. Gardeners know it as a nuisance that keeps coming back no matter how often they dig it out. Old medical texts, though, gave this root its own entry among their medicinal ingredients.
Cogon Root in the Donguibogam
The Donguibogam lists mogeun (茅根) in its grasses section (chobu, the part devoted to herbaceous plants) and gives its Korean name as ttippuri, "cogon root." It describes the root's nature as cold, adding that some call it cool instead, and its flavor as sweet and nontoxic. The book identifies it as baengmogeun (白茅根), "white cogon root," and notes that it grows everywhere. For preparation, it says to dig the roots in the sixth lunar month and dry them in the sun. In the same entry, it lists the flowers (mohwa) and the sharp young shoots (mochim) separately.
These descriptions follow the classification system of an early 17th-century medical text, so they don't reflect modern medical judgment. "Cold" and "sweet" were categories the old texts used to sort medicinal ingredients, and they can't be read as evidence that cogon root cures any particular illness. You'll find the original text and our commentary in the cogon grass root entry in Homiclub's Donguibogam. The root in baengmogeun-cha, the cogon root tea many Koreans drink today, is this same root.
How It Compares with Modern Analysis
On sweetness, the old record and modern research agree. The Donguibogam called the root sweet, and composition studies trace that sweetness to sugars stored in the rhizome. The book's note that the plant grows everywhere also matches today's ecological records. Cogon grass spreads quickly through its rhizomes and is considered a hard-to-control weed in many parts of the world. In the United States, it's on the federal noxious weed list.
Other parts of the record are harder to compare. Researchers have reported isolating triterpene compounds from cogon grass rhizomes. Those reports are compositional analyses, though: they describe what's in the plant, not what those compounds do in the body. The rhizome also contains potassium, a mineral common in plants, and dietary fiber, which gives it its tough, stringy texture. The old classification of the root as "cold" can't be translated into a list of compounds like this.
In the Garden, Stop the Spread First
Cogon grass thrives on sunny banks. In the Northern Hemisphere, plant it in March or April, and harvest in April–May and again in July. The sixth lunar month usually falls around July on the Western calendar, so the summer harvest lines up with when the Donguibogam said to dig the roots. In the Southern Hemisphere, shift each window six months later. You can look up planting and harvest months anytime in the cogon grass entry in our crop guide.
The rhizomes creep sideways and spread, so don't plant cogon grass in open ground. Use a large pot or box with a solid bottom instead. In places where it's designated a noxious weed, such as the United States, planting or moving it may be prohibited, so check your local regulations first. If it has already spread through your plot, save the rhizomes you dig up. Wash off the soil and dry them thoroughly in the sun, and you've prepared them just as the Donguibogam describes. Don't eat any roots dug from roadsides or from ground that's been sprayed with pesticides.
Brewing a Mild Tea
To make tea, simmer the dried rhizomes in water. Here are a few ingredients that pair well, along with some tips for drinking it.
- With jujubes: Simmer the dried rhizomes with a few dried jujubes (Korean red dates) to tone down the earthy taste and add sweetness. Use plenty of water and keep the heat low.
- With roasted barley or brown rice: Roasted grains add a nutty, toasty flavor that makes the tea easy to sip throughout the day, like water. Grains make it spoil faster, so drink it the same day you brew it.
- Chilled: Let the brewed tea cool, then chill it for a refreshing summer drink. It's faintly sweet on its own, so there's no need to add anything. Keep it in the fridge and finish it the same day.
Enjoy cogon root tea as a drink to savor, made from a root with a long written history. If you're taking medication or have a chronic health condition, talk to your doctor before drinking it.
If you turn up white rhizomes while tidying your garden today, rinse a handful and lay them out in the sun to dry.
