When a plant is growing in a place where it is unwanted, we call it a weed. Many weeds were brought to our area as garden plants that have now spread into the wild. These plants are often adaptable, hardy, and have the ability to choke out native species. Invasive weeds are particularly aggressive non-native plants and are considered noxious if they are harmful to the environment, people, livestock, and/or agriculture. An example is Himalayan knotweed, which can take over stream corridors choking out native plants and reducing wildlife habitat. Some weeds are legally listed by the state and county as ‘noxious weeds,’ these weeds are required to be controlled. Check with your county Noxious Weed Control Board www.nwcb.wa.gov/ to identify listed noxious weeds.
Some methods to managing weeds include:
- Avoid disturbing the soil. Many weed seeds remain in the soil, waiting for light to initiate germination. If left undisturbed, they will likely remain dormant. Avoid the use of tillers, and hand-cultivate lightly, if at all.
- Use organic mulch. Smothering the weed seeds with organic mulches (straw, layers of newspaper, mulch, and cardboard) will block the light out and will eventually degrade, improving the soil.
- Use wet paper or cardboard. Wet the paper or cardboard, and the ground beneath, to keep it from blowing away. Spread mulch 2–4 inches deep above the cardboard, which will retain moisture while suppressing weeds. Be sure to use straw, not hay (which contains seeds that will sprout).
- Remove invasive weeds as quickly as possible. Invasive weeds should be removed as quickly as possible before they spread. Other weeds however, like non-spreading annuals, may be beneficial by allowing their roots to hold valuable topsoil in place and not allowing it to be blown or washed away.
- Think twice before removing weeds from bluffs. When considering removing weeds from a bluff, exercise extreme caution. Some weeds have deep taproots and removing them could cause erosion or even a landslide. Sometimes cutting the weed off at the ground (scotch broom) will work, but sometimes it is best to leave the weeds on bluffs alone.