An old adage among gardeners (and botany professors) is that the definition of a weed is any plant you don’t want. That being said, there some weeds that are quite pretty and others that are just an annoyance because you didn't plant them and don't want them. Then there those that are blight to the environment.
Many King County property owners do not realize they have a legal obligation to remove certain weeds from their property. Noxious weeds are separated into classes A, B, and C based on distribution, abundance, and level of threat (how dangerous the plant is to humans, animals, private and public lands, and native habitats).
Noxious weeds are non‐native plants that, once established, are highly destructive, competitive and difficult to control. They have economic and ecological impacts and are very difficult to manage once they get established. So kill ‘em while they’re young is the message here. Non-native invasive weeds across the United States cost an estimated $26.4 billion per year in agricultural economic losses, according to the county.
All Class A weeds must be removed, according to King County Washington State Noxious Weed Law RCW 17.10.
It’s unlikely a property owner is going to be sited for non-compliance of weed removal, but with Earth Day being celebrated April 22, why not lend the local environment a hand by removing invasive exotics that are crowding out native plants? You can find a list of weeds to eradicate at King County’s Noxious Weeds Website. There are also photos and video to help identify the pernicious interlopers.
Here is a short list of the worst offenders on the Eastside:
Tansy ragwort is an invasive, toxic biennial weed from Europe most often found in pastures and along roads and trails. It is a host plant to the larvae of the cinnabar moth who like to munch on its leaves. Problem solved? No, not only will the moth larvae eat the weed, but any Dusty Miller plants you have in the garden also and you will still have the weeds. Tansy ragwort is a Class B Noxious Weed in Washington State and control is required in selected counties in the state, including King County.
Purple loosestrife is another Class B noxious weed found throughout the state and control is required in King County. Amazingly, Purple loosestrife is sometimes sold as a garden ornamental at uninformed nurseries. This plant is on the Prohibited Plants List, and it is illegal to buy, sell, transport or offer this plant for sale in the state of Washington.
Giant hogweed is a Class A Noxious Weed in Washington State the potential for significant impact to state resources. Public and private landowners are required to control this plant when it occurs on their land. But be careful if you have it, this plant is difficult to distinguish from the native plant cow parsnip, it is recommend contacting the noxious weed program for a positive identification and advice on control methods before removing.
Giant knotweed here in the Pacific Northwest, there are three closely related species of invasive knotweed that are difficult to tell apart and that share similar habitat, impacts and control methods. They are all large, robust perennials that spread by long creeping rhizomes to form dense thickets. All three species of knotweed are Class B noxious weeds on the state’s noxious weed list and control of these aggressive species is strongly recommended but not required in King County. However, if you do not remove them they may take over your garden.
Garlic mustard will be the bane of your garden if not controlled. It is an invasive non-native biennial herb that spreads by seed. It is difficult to control once it has reached a site; it can cross-pollinate or self-pollinate, it has a high seed production rate, it out competes native vegetation and it can establish in a relatively stable forest understory. It can grow in dense shade or sunny sites. The fact that it is self fertile means that one plant can occupy a site and produce a seed bank. Plant stands can produce more than 62,000 seeds per square meter to quickly out compete local flora, changing the structure of plant communities on the forest floor. Garlic mustard is also allelopathic, producing chemicals that inhibit the growth of other plants and mychorrizal fungi needed for healthy tree growth and tree seedling survival.