Japanese Knotweed shoots in the spring
Japanese Knotweed Fallopia japonica is growing well in the Hudson Valley. Too well – it’s everywhere, including people’s gardens. It forms large stands, preventing all other plants from growing and eliminating habitat for wildlife.
If it’s growing on your property, remove it as soon as possible before it becomes a large clump which is much harder deal with.
The semi-woody stem is hollow
- A herbaceous perennial that can grow over 5′ tall with stems 2″ wide.
- Hollow stems look a little like bamboo.
- In spring the shoots are a reddish color
- The green stems have enlarged leaf nodes and may have red spots
- The green leaves are alternate, 6″ long, 3-4″ wide and broadly ovate
- In August, the flowers are greenish-white panicles in the axils of the leaves
- In the fall the foliage dies back, leaving the dead woody stems standing
Clumps of Japanese Knotweed in late spring
Barbara Bravo an experienced Hudson Valley gardener, Garden Coach and Master Gardener, recommends these steps for removing the plant.
- Mowing or cutting to ground. To be effective, continue all season.
- Use heavy black plastic sheets to smother plants
- For large stands, the best method is to cut stems off at about 3′ high just below a stem node – use a squirt bottle and fill the hollow stem up ¼ of the way with 25 % Glyphosate (Use Rodeo if in a wetland or near water). Follow all instructions on the product label exactly to avoid contamination and over-use of chemicals.
- In all cases, dispose of cut stems properly – the plant can resprout from stem or root pieces that are left on the ground.
- Do not put the plant on a compost heap because it is possible to spread the plant when applying compost
- Put the plant in a sealed bag in your trash can for garbage removal.
- Complete removal may take several years, inspect the area often for regrowth and continue the removal process if needed.
- Alternately, hire a professional Invasive Plant Removal company
Japanese Knotweed flowers in August
In the fall the foliage and flowers die back
Woody stem in the fall
How does this plant spread?
- This plant has a horizontal, underground plant stem (rhizome) that produces a shoot and root system for a new plant. This rhizome can grow under surfaces such as concrete, bricks etc. until it finds a space to start a new plant.
- It is also spread by seed
New plants sprouting from rhizomes. These new plants are growing in October!
How did this plant arrive in the Hudson Valley?
Japanese Knotweed is native to Japan, China, Korea, and Taiwan and was brought to America in the late 1800s as a garden plant. It now grows wild because it can grow in a variety of soils, in sun or part shade and thrives in this climate.
Japanese Knotweed stems in October
Foliage has died back, leaving the dead stems.
Preventing the spread of Japanese Knotweed
In her excellent lecture about invasive plants in the Hudson Valley, Barbara Bravo explained “Gardeners are the first line of defense against invasive plants, if you see a plant that is thriving and you do not recognize it, do some research to identify the plant. If necessary, remove it”
Need some help with this plant?
Contact your local Cornell Cooperative Extension Office
Contact Barbara Bravo at Enter the Garden
For help identifying a plant, post a picture on the Plant Identification Facebook page
Foragers of wild plants can find recipes for eating Japanese Knotweed here
For professional plant removal, contact Poison Ivy Patrol, this business uses non-chemical removal methods