Giant knotweed is an exotic weed in Illinois. The Illinois Exotic Weed Act prohibits the sale or distribution of this plant in Illinois. This plant mainly spreads by vegetative propagation, where fragments of stems or roots are transported to new areas by wind, water, or sometimes animals. Giant knotweed also has rhizomes that grow horizontally underground and allow the plant to spread further. The seeds are not highly fertile, and therefore do not pose a threat as a means of spreading. It prefers moist environments with full sun, commonly growing in disturbed areas or near bodies of water (riparian areas). It was originally brought over from an island in Japan called Sakhalin, but today has spread to the northeastern and northwestern parts of the United States.
Giant knotweed’s dense, thick roots, have the ability to penetrate almost any surface, including pavement. This, coupled with the ability to spread rapidly, allows this plant to quickly overtake natural and cultivated areas. It can shade out nearby plants, suppress their growth (allelopathic properties), and clog waterways, impacting ecological or human health.
As a good alternative, red-osier dogwood (Cornus sericea) can be planted instead for its similar appearance, size, and erosion control properties. There are a number of native and non-native species that could be used in place of giant knotweed. More desirable species may be found using the online Search Trees and Plants page of the Arboretum website. Before purchasing or planting, be sure to check for any local or state guidelines on this species, and ensure that this plant is suitable for its habitat by checking its attributes at mortonarb.org or plants.usda.gov.
- Family (English) Buckwheat
- Family (botanic) Polygonaceae
- Hardiness zones Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7, Zone 8
