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KNOTWEED
 Himalayan knotweed, near river  Japanese knotweed, isolated stand Four species of knotweed have been very invasive in the Pacific Northwest: Japanese, Giant, Himalayan, and a hybrid variety. Also known as "elephant ears," "Mexican bamboo," "Japanese bamboo," and "fleeceflower," these plants grow in dense clusters, ranging from 6' (Himalayan) to 10' (Japanese) to as large as 15' (Giant) in height.
They have triangular to heart-shaped leaves 6" (Japanese) to 12" (Giant) long, and produce clusters of small flowers which may be green, white, or pink. The stems of these plants are similar to bamboo, and often have a reddish color. All four are perennials. Growth begins in early spring, and is very rapid until the plants reach maximum height in June. Flowers may appear anytime from July through September, followed by seed production and dieback in late fall.
 Japanese knotweed, close-up of branches  Japanese knotweed, near river Knotweed was introduced here as an ornamental from Asia by way of the UK, and has been able to spread rapidly in the Pacific Northwest. Because tiny fragments of root as small as ½" can re-sprout and form new colonies, it has moved quickly through watersheds. Other plant parts can also re-root, which has allowed knotweed to spread downstream during flood events.
Once established, it grows and expands quickly, crowding out native vegetation and preventing new trees from growing up to replace ones that die. This is bad news for wildlife; native trees and shrubs provide animals and birds with food and shelter, as well as the shade, wood, and erosion control that make streams healthy for fish. By contrast, knotweed roots are very poor at holding soil; although they are deep, they break apart easily, allowing rapid erosion of streambanks.
 Japanese knotweed, close-up of stems Noah Jenkins, our AmeriCorps member, will be contacting creekside residents by mail and in person in the coming months to seek cooperation in finding where knotweed is in the Johnson Creek Watershed and beginning a program to eradicate it. He will be asking landowners' permission to look for knotweed on their property; if it is found, he will treat it for them if they so desire. All FREE of charge! Because knotweed is extremely difficult to control by any other means, he will primarily be using an herbicide approved by NOAA for use near salmonid-bearing streams.
We need your help in locating stands of knotweed. If you know you have this plant on your property, or have seen it in the watershed, please contact Noah at (503) 652-7477 or . By locating and treating all stands in the watershed, we will be able to keep this plant from getting out of control.
This program is a joint partnership between the Johnson Creek Watershed Counci, and the East Multnomah Soil & Water Conservation District. Funding has been provided by the Oregon Watershed Enhancement Board. Feel free to contact Noah if you would like more information or have any questions about this project.
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