The foliage beauty of the variegated Japanese knotweed (Fallopia japonica 'Variegata') is accentuated by the dark green to reddish stems that hold the creamy white and green leaves. A perennial native to extreme eastern Asia, it grows from a rhizome, or underground rootlike stem. In some soils and climates, the rhizomes spread prolifically, causing this plant to be considered a weed.
Japanese knotweed is a member of the flowering plant family Polygonaceae, the smartweed family. Its scientific name is Fallopia japonica, with a previous but still synonymous name of Polygonum cuspidatum. Variegated varieties include cultivars Variegata and Milk Boy. Additional English common names for Japanese knotweed include Mexican bamboo, donkey rhubarb, fleece flower and German sausage.
Japanese knotweed is native to Japan, Sakhalin Island, the Kurile Islands, the Korea Peninsula, southwestern China, Taiwan and Vietnam. This plant is a pioneer species on volcanic soils as well as establishing quickly and abundantly in marginal or waste areas like abandoned lots or alongside roadways.
Japanese knotweed is an herbaceous perennial that grows from stout, large rhizomes, which are rootlike underground stems. A hollow, smooth stem emerges from each rhizome and then branches out to carry many broad but oval and pointed leaves. The plant quickly can grow in late spring to its mature height of 3 to 9 feet; in cultivated gardens the plant tends to grow much taller than it would in its native habitats in eastern Asia. The variegated form of Japanese knotweed has foliage that is irregularly blotched with both creamy white and light to medium green. The stems, in contrast to the foliage, are dark glossy green or blushed with tones of red or pink.
In midsummer the Japanese knotweed plant bears stringy flowers of creamy white from the tips of its branches. The fleecelike drooping flower clusters to 6 inches in length are either fully male or female in gender, with each plant bearing only one sexed flower type. After pollination by wind and/or insects, many shiny, dark brown fruits form.
Variegated Japanese knotweed grows best in acidic, moist, well-draining soils that are fertile. However, it is quite tolerant of a wide array of soil types from coastal sands to inland infertile and dry to almost soggy. Full-sun exposure, meaning at least 6 to 8 hours of direct sunlight each day, is ideal. Partially shaded locations can ensure no browning of the white leaf areas on the variegated foliage, especially if in a hot summer climate or growing in a dry soil. This plant is considered hardy in USDA Hardiness Zones 4 through 9. In cold winter regions, the dormant rhizomes should be mulched heavily if snow cover is not expected.
Although the main species of Japanese knotweed is often regarded as a pesky weed, the more ornamental variegated selections are best used in gardens. These selections usually are not as aggressively seeding into the landscape, but the plant and surrounding soil should be monitored and unwanted seedlings removed. Use this tall-growing perennial as a background filler in a mixed border or as an individual specimen. Florists find the summertime flowers long-lasting in arrangements; the dried seeds also can be preserved and used in decorations.