Answer: Japanese knotweed is one of those plants that has escaped cultivation and become a noxious weed in some parts of western Washington. Birds can transport seeds quite a distance, depositing them where they congregate; most often near bodies of water or in forested areas. When this happens, the plant can grow unchecked until it finally crowds out native vegetation. I suspect that it also travels when prunings are dumped in forested areas instead of being disposed of properly. Japanese knotweed is a lovely plant, and you can keep it under control in your own garden by pruning it back when it gets too large. Just be careful with the prunings - either lay them out in the sun until they are completely dead before disposal, or place them in a plastic bag and set it in the sun until the contents are cooked. As long as you're a responsible gardener, you should be able to enjoy your plant without adversely impacting the local ecosystem.
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