Japanese Knotweed
Reynoutria japonica (synonym Fallopia japonica) · Herbaceous perennial (shrub-like growth pattern)
Plant Family
Polygonaceae
Tree Category
Invasive Plant / Herbaceous Perennial
Variety / Cultivar
Standard species
Hardiness Zones
USDA Zones 3-9; extremely adaptable to various climates and temperature extremes.
About This Tree
While often behaving like a shrub or small tree in height, it is a rhizomatous perennial. It forms dense thickets with bamboo-like hollow stems and a spreading, arching habit. It is known for its aggressive growth rate and ability to penetrate through concrete and asphalt.
Leaf Characteristics
Simple, alternate arrangement; broadly ovate to heart-shaped with a truncated base; 3-6 inches long; bright green color; smooth margins (entire); distinct pointed tips.
Bark Characteristics
Actual bark is absent; stems are bamboo-like, hollow, green with reddish-purple speckles, turning brown and brittle in winter.
Growing Information
Origin Region
East Asia (Japan, China, Korea); highly invasive in North America and Europe
Growing Season
Emerges in early spring (March-April), flowers in late summer (August-September), dies back to ground after first frost.
Sunlight & Water Needs
Full sun to partial shade; highly adaptable; prefers moist soils but is extremely drought-tolerant once established via deep rhizomes.
Mature Size
Typically 7-10 feet tall; spreads indefinitely via underground rhizomes that can reach 60 feet in length; grows very fast.
Special Characteristics
Highly invasive; extremely difficult to eradicate; stems contain resveratrol; historically used in traditional medicine, but now primarily managed as a destructive weed.
Wildlife & Ecology
Provides late-season nectar for honeybees and pollinators; however, it generally degrades ecosystems by outcompeting native vegetation and reducing biodiversity.