Policeman's helmet, also known as jewelweed or Himalayan balsam, thrives in moist areas and riparian zones. Although sometimes sold as an ornamental, this native of Asia has been added to the Washington State Noxious Weed list due to its invasive nature. In Britain, where the climate is similar to the Pacific Northwest, this plant is considered extremely invasive and is one of the "top 20" non-native weeds.
Legal status in King County, Washington
Class B noxious weed. Property owners in King County are required to control this plant. This species is also on the Washington quarantine list (known as the prohibited plants list) (external link) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts, seeds in packets, blends or "wildflower mixes" of this species, into or within the state of Washington.
Biology and morphology
Policeman's helmet is an annual that germinates from February through March and flowers from June to October. Growing up to 10 feet tall, the upright stems are hollow with a purple or reddish tinge; leaves are oblong to egg-shaped, with serrated edges, with white, pink or purple flowers resembling an old-fashioned English policeman's helmet. A single plant can produce up to 800 seeds, which are viable for 18 months or more and can even germinate under water. Since the plant often grows along streams and ditches, seeds spread quickly downstream. When touched, the mature seedpods split and eject seeds up to 20 feet. This trait has earned the Impatiens family the name of "touch me not."
Additional information on policeman's helmet
What to do if you find this plant in King County, Washington
Please notify us if you see policeman's helmet growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because policeman's helmet is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as policeman's helmet in order to help us and others locate new infestations in time to control them.
Policeman's helmet photos - click thumbnail for larger image