Humulus scandens aka Japanese Hop

Humulus scandens, or Japanese hop, belongs to the hemp family, Cannabaceae. Sources also name it Humulus japonicus. Its native range spans temperate eastern Asia, from Russia to northern Vietnam. It grows in thickets, beside roads, and along streams. It has spread into eastern Canada and the United States. It also occurs outside its native range in Europe.

This fast-growing annual vine has a taproot and twining stems. It climbs supports or trails across the ground. Stems can reach 35 feet [10.7 metres]. The sources give no typical garden height or spread. Green stems may show purple streaks and have four angles. Stiff, branched hairs help the plant climb. Opposite green leaves have a heart-shaped base and toothed edges. Most leaves have five lobes, though some have three to seven. Hairs give the leaves a rough feel. Leaf stalks are often longer than the leaf blades.

Small greenish flowers appear from midsummer into fall. Male and female flowers grow on separate plants. Male flowers form upright, loose panicles near the leaves. Female clusters hang down and have overlapping, hairy bracts. These bracts may be green or purple. Female flowers lack petals and sit beneath the bracts. The fruit is an egg-shaped, yellow-brown achene. Papery bracts surround the fruits, which appear in fall. Wind and water spread the seeds to new sites.

Japanese hop grows in sun or partial shade. It accepts clay, loam, and sandy soils with good drainage. Moist, fertile loam supports its strongest growth. It tolerates drought and neutral to alkaline soil. NC State lists USDA zones 4–8 for this plant. Some plants survive mild winters despite their annual life cycle. The vine can provide a screen or ground cover. Its leaves feed several kinds of butterfly caterpillars. Young leaves and shoots have recorded food uses when cooked. Seed oil has been used to make soap. Traditional uses include a diuretic and urinary tonic.

Its rapid spread makes it a poor planting choice. Dense mats can crowd out other plants. NC State reports no known disease or insect problems. It identifies the vine as invasive in several US states. The RHS reports UK controls, including a ban on sale. Pulling plants before seed forms can help limit spread. Remove as much of the root as possible. Contact can cause skin irritation and blisters. NC State rates its poison effects as low severity.