Garden Ecology - Publications

Japanese Knotweed
Polygonum cuspidatum aka Fallopia japonica

This highly invasive plant is a herbaceous perennial which was once
endemic to Japan and Southeast Asia. British botanists first brought the plant to England as an ornamental plant in or around the year 1825. Japanese Knotweed began showing up in North America in the early 1900’s, and can now be found in 37 states! This plant is a powerful example of how an irresponsible international plant market can have a huge impact on our local ecology.

If you asking yourself - ‘What exactly is an invasive plant ?’, then I’m glad you have come to this web-site because just by knowing more about invasive plants, like Japanese Knotweed, you are taking the first step to controlling their spread. Invasive plants form two broad categories: First are the native plant species that, for some environmental reason, are growing out of control and spreading beyond their normal habitat. The second group are foreign plant species transported out of their natural environment and introduced into an new one. In their new home envisages grow like crazy.
Japanese knotweed is an example of the latter type; words like
“exotic invasives” or simply “exotics” are often used for this type.

Research has shown that in its native habitat, Japanese Knotweed has many factors controlling its growth. These natural controls are part of nature’s balance and include funguses (fungal pathogens), leaf chewing, and leaf and stem boring insects, as well as other insect and animal predators . Since many of these control factors are not present in the United States, Japanese Knotweed is able to grow out of control. On Long Island this plant is spreading quickly, taking over our native plants and causing damage to wetlands, gardens, sea shore environments and farm fields.

IDENTIFICATION TIPS

Japanese Knotweed flowers in mid August to mid September. One of its common names is the Japanese fleece flower, due to its fleecy white flowers.

Japanese knotweed can be identified by its segmented stems displaying large alternating leaves.

This plant has roots called rhizomes which grow horizontally just below the surface of the soil. New top growth and new roots grow out of the rhizome as the plant moves across the landscape. Rhizomes are an important factor to the success of this plant, because they are hollow. This allows the plant to bring air down into the soil. Air is a critical element in the kind of soils good for plant growth. This is why Japanese Knotweed is such a tough competitor in poor soils and challenging wetland conditions. By pumping air into poor soils this plant changes the soil conditions to suit its quest for world domination.

In early spring Japanese Knotweed shows red leaves as the new shoots begin to break above the soil. Harsh roadside conditions are no problem for this very tough invasive.

If your on the look out for Japanese Knotweed, you’ll notice more often than not you’ll find it along road sides. This is often where new stands of the plant get started. Transport of cut stems and roots as yard waist by homeowners and landscapers are an unfortunate vector (delivery system). If a small segment of root should fall off the back of a truck and blow to the side of the road, next year there may be a medium size plant growing there! This carelessness can result in not only a negative impact to our ecology. The economic costs are also high since many visitors come each year to our area for its beautiful and natural scenery. Scenery often viewed along our many rural roads.

Here is a really big stand. These plants have grown tall enough to block the view of Big Fresh Pond in Southampton. The economic impact of this one plant species in the United States is not well understood, but all you have to do is use your imagination. Britain has been fighting this plant for longer than we have and they estimate the spending to be 10 million dollars annually!!

That's a lot of weeding!

Here we are along Brickyln Rd. in Bridgehampton, NY where there is a newly landscaped site with some young knotweed starting to grow. This is more than likely a case of the landscaper unknowingly buying soil or fill that was contaminated with Japanese Knotweed roots and stems. Shoddy landscape practices are an increasing vector for the plant. If not controlled professionally and rapidly the owner of this property may be dealing with this problem plant for many years to come.

Evidence of invasive plants can lower the value of a property, since effective control can take years and many thousands of dollars.

The best way to control knotweed once you find it is good old fashion excavation and removal. Catching the plant still small helps enormously. To do this right you’ll have to dig up all the soil within a few feet of the unwanted plant, constantly checking to see if you have removed all the rhizomes. Every part of the plant should be bagged and sealed. Very Important: do not to take this waste to another part of your property or a natural area for composting. Carefully deliver this the invasive plant waist to the local landfill and inform attendant that you have invasive plant waist. Most landfills are trained to dispose of invasive plants properly so that there’s no opportunity for the plant to spread.

Please keep an eye out for this plant. If allowed to grow unchecked,
Japanese Knotweed will eventually grow into huge stands, blocking views, light and destroying natural landscapes. Please help preserve the beauty of our Island. To learn more about this plant and other invasive species go to: http://www.invasives.org

If you suspect that you may have japanese knotweed on your property and would like more advice on how to deal with it, please feel free to contact us.