Can i put japanese knotwood that i’ve cut down in my yard waste bag? My neighbour (we both have the plant coming up in our yard) sent me some information from your site stating that it’s hard to dispose of as it will send down roots everywhere. But what if I disposed of it in yard waste bags and kept those bags on asphalt? (about 10 feet from green space). I’m just wondering if I can do that or if I have to go the black tarp route. Thanks so much!)
Thank you for contacting Toronto Master Gardeners.
You are dealing with an extremely invasive weed and I am pleased you are taking the time find out the correct ways to dispose of it.
Knotweed, Fallopia japonica, is covered extensively by the Ontario Invasive Species Council as it is so invasive and so difficult to eradicate. It usually takes several years of effort to totally remove an established patch of Knotweed.
Cutting back and digging up roots once will have the opposite effect to the intention and the plant will be revitalized and come back stronger than before. There are chemical ways to try and manage the weed and there is also mowing and the barrier method you mentioned. You may find it takes a combination of approaches to have the most effect. You would need to consult a local nursery to find out what chemicals are available and allowed to be used in your area. Another important issue is preventing spreading of the weed. Mowing and tarping will weaken the Knotweed and help curb spreading. You mention in your first post that a neighbour shares the same invasive problem. Working together will certainly give you a greater chance of success.
You are correct about disposal. The heavy black bags will need to be closed and set in the hot sun for at least a week before they are sent to landfill.
The following articles from Ontario Invasive plants have detailed information on eradication for both small and large infestations and outlines in details the various techniques to use. It also includes a hotline you can call to report the presence of Knotweed and get further information.
Good luck I hope you succeed!