About 14 species of the genus Pueraria grow in southern and Southeast Asia, Japan, China and Pacific islands. The genus is a member of the bean family (Fabaceae). Most Pueraria species are woody, climbing vines, but two species are shrubby. Some of the species have a restricted geographical location while humans moved other species from place to place because of their food value. The most widely distributed species, even in ancient times, is kudzu (Pueraria montana and Pueraria montana var. lobata). It is the only Pueraria species common in the United States.
Introduced to the United States about 1876 as an ornamental plant, kudzu was promoted for forage and for erosion control. By the 1950s, however, its invasive qualities emerged, and planting kudzu was discouraged. The vine had a firm hold in wild lands by then, though, and continues to spread. Kudzu is a serious threat to natural habitats, especially in the U.S. Southeast and Oregon. It is listed as an exotic invasive species and considered a noxious weed.
One factor that makes kudzu invasive is its fast growth. It can add 1 foot of growth per day and become 33 to 99 feet long in one growing season. It twines around tree trunks, smothers tree canopies and engulfs small plants. It has hairy stems that bear leaves divided into three leaflets; each leaflet is up to 6 inches long. Kudzu pours its food reserves not only into prolific growth but into the formation of its large, tuberous roots. When in contact with soil, its stems root every few feet, and each rooted area, called a crown, can form a new plant.
During summer in the warmest areas of kudzu's range, the plant produces red to purple, pealike flowers in clusters on stalks that grow from stems. The flowers' fragrance is reminiscent of grapes. Kudzu doesn't flower when it grows as a ground cover or usually when it's under 3 years old, and only a climbing specimen produces seeds. Flattened seedpods that resemble bean pods follow the flowers. The seedpods are covered with dense, golden-brown hairs and are about 3 inches long.
Kudzu grows best in areas with mild winters, long growing seasons and hot summers, and where the annual rainfall is greater than 40 inches. It is hardy in U.S. Department of Agriculture plant hardiness zones 5 through 10. The largest stands of kudzu occur in open areas, such as roadsides and fields, from which it spreads to forest edges. Although it grows best in deep, loamy soils, kudzu, like other bean family members, can add nitrogen to soil, which allows it to grow in poor soil.
Controlling kudzu is a problem of national concern. In many states, it is illegal to propagate, grow or sell kudzu. Once established, the plant tends to persist due to its food-storing roots, multiple plant crowns and ability to regenerate. Prevent its establishment whenever possible. Removing kudzu completely requires taking out every one of its rooted crowns; eradicating a well-established patch of kudzu may take 10 years, according to a U.S. Forest Service document. Repeated intensive grazing for several years by sheep or goats depletes kudzu roots' food reserves and can help control the plant.
- Pueraria: The Genus Pueraria; Wing Ming Keung
- Columbia University: Introduced Species Summary Project -- Kudzu (Pueraria Montana)
- Missouri Botanical Garden: Pueraria Montana Var. Lobata
- U.S. Forest Service: Pueraria Montana Var. Lobata