In October in the Northern Hemisphere, the kudzu leaves on the hillside beyond the garden fence start to turn yellow. The vines that carried purple flowers in late summer drop their leaves once the frost comes. Kudzu (Pueraria lobata) is a vine in the legume family that grows wild on the hills and fields of Korea, China and Japan. Its thick roots end up on the table as kudzu tea and kudzu-starch noodles. When the leaves fall, digging season begins.
Galgeun in the Dongui Bogam
The Dongui Bogam, the Korean medical classic compiled by Heo Jun, lists kudzu root in its herbs section (草部) under the name galgeun (葛根). The original entry reads "性平(一云冷) 味甘 無毒." This means the root is neutral in nature, sweet in taste and nontoxic. The phrase 一云冷 adds that some sources call it cold. The entry says the plant grows in the mountains and is found almost everywhere, and it gives a second name, nokgwak (鹿藿).
The text also says when to harvest and how to pick good roots. Dig them on the fifth day of the fifth lunar month (usually late May to June on the Western calendar) and dry them in the sun. Roots that grow deep in the ground were considered the best. The flowers have their own entry under the name galhwa (葛花). You can read the original text and commentary in Homiclub's Dongui Bogam entry on galgeun. Keep in mind that this is a description from a historical medical text and is not the same as modern medical advice.
What the Chemistry Says
Several research groups have isolated isoflavones from kudzu root, puerarin above all. Puerarin is the isoflavone glycoside kudzu root is best known for. Daidzein and daidzin also turn up, and both are commonly reported in legumes. The root also holds starch, which is how the plant stores carbohydrate, plus a tough fiber that stays stringy however long you chew.
In places, the old record and modern findings agree. The Dongui Bogam preferred roots that grow deep in the soil, and modern researchers have found that compound levels vary with the part of the plant and the time of harvest. Both point out that where and when you dig changes the root.
The differences are just as clear. The old text described the root by its nature and taste, while modern analysis measures which compounds the root contains and how much of each. These studies don't settle what those compounds actually do in the body. The harvest seasons differ too. The Dongui Bogam called for roots dug in early summer and dried for medicine. Households that make kudzu starch have long dug from leaf drop until early spring, because the roots are said to hold the most starch then. Roots for drying and roots for starch were simply dug at different times of year.
How you eat kudzu may also change what your body takes in. Kudzu tea is made by simmering the root in water, so water-soluble compounds such as puerarin probably end up in the cup. Kudzu starch is made by soaking the crushed root and letting the starch settle out several times. Much of the water-soluble material is likely poured off with the clear water on top, leaving mostly carbohydrate. If you take any medication or an isoflavone supplement, talk with your doctor or pharmacist before you start drinking strong kudzu decoction every day.
Before You Plant It
In the Northern Hemisphere, kudzu goes in the ground in March or April. Over the summer, though, the vines grow fast, covering fences and nearby crops, and they root wherever a stem node touches the soil. Outside its native East Asia, several regions, including the southeastern United States, manage kudzu as an invasive species. Before planting, check whether it's allowed where you live.
If you decide to grow it, use a large container with a solid bottom or a raised bed walled in on all sides instead of open ground. Train the vine up a single support, and cut back any runners that creep sideways as soon as you see them. When the flowers fade and pods form, it's safest to pick the pods before the seeds drop. The roots usually take several years to get thick enough to dig.
In the Northern Hemisphere, harvest from November through February. After all the leaves have fallen, dig up the roots and wash off the soil. Slice any roots meant for tea thinly and dry them in the sun. If growing kudzu sounds like too much work, store-bought dried kudzu root or kudzu starch works just as well.
Kudzu Tea and Kudzu Starch
For kudzu tea, thinly sliced dried root gives up its flavor fastest. Simmer it gently over low heat with a few jujubes (dried red dates), then stir in honey to soften the bitter, slightly astringent finish. A couple of slices of ginger add a warm, spicy note that makes the tea easier to drink. Ginger gets sharper the longer it boils, so add it at the very end and then turn off the heat.
Kudzu starch, called galbun in Korean, is made by pounding fresh roots, soaking them in water, and collecting and drying the starch that settles to the bottom. It doesn't hold together well on its own, so cooks mix in buckwheat or wheat flour to make noodles. For dasik (a Korean confection made by kneading a powder with honey and pressing it into a mold), the starch is mixed with honey and pressed into a carved dasik mold.
Look up planting and harvest months in our kudzu crop guide, then pick up a bag of dried kudzu root and brew a pot of jujube kudzu tea.
Source: Heo Jun, Dongui Bogam, Tangaek-pyeon (materia medica volume), herbs section (草部), "Galgeun" (published 1613).
