April Weed of the Month: Japanese Hops

When you hear the word "hops," you might think of beer. Hops are used in beer production to add bitter, floral, fruity, or citric flavors and essential oils for preservation. However, Japanese hops (Humulus japonicus) lack an essential resin for beer production. Common hops (H. lupulus) are a similar native species and can be used for beer production. Introduced to North America as ornamental vines, Japanese hops are native to eastern Asia. Unfortunately, Japanese hops escaped cultivation and have become invasive.

Japanese hops have distinct bracts where the leaf and petiole attach to the stem. The leaves have toothed edges with 5 to 9 lobes arranged palmately (shaped like a hand with fingers extended), while common hops only have up to 5 lobes. Japanese hops have both male and female vines. With female vines, seeds are produced in conical husks; male vines produce pollen from flowers. Hooked hairs on the stem and leaves help the vines climb but can irritate human skin after contact.

Seeds from the vine are easily dispersed by wind, water, wildlife, vehicles, and equipment. This allows Japanese hops to grow very rapidly. In just one season, they can grow up to 35 feet long. The vines twine around to climb vegetation and structures, capable of smothering desirable vegetation and producing dense mats several feet thick.

Japanese hops are herbaceous annual vines in Minnesota but can be perennial in warmer climates. They thrive in partial to full sun including riparian areas, roadsides, grasslands, and forest edges. Japanese hops has been found in southeastern Minnesota along the Root and Mississippi rivers and in the city of Winona. Most infestations are on riverbanks and creep into adjacent forest understory.

If you suspect you have found Japanese hops, please take pictures of the plant, note the exact location, and report to Arrest the Pest at arrest.the.pest@state.mn.us. If you have questions or would like more information, please visit the Minnesota Department of Agriculture or the Midwest Invasive Plant Network websites.