Scotch Broom: The Yellow, Fuzzy, Tenacious Weed

Managing Scotch broom is critical to restoring prairie and oak habitats.

Photo credit: Norah Kates
Scotch broom blooms between April and June. Its furry, black seed pods can produce up to 10,000 seeds each year.

You’ve seen the masses of bright yellow flowers lining the highway, the bundles of tough stalks overtaking prairies, forest clearings, and other open spaces. Introduced by Europeans to North America in the mid-19th century, Scotch broom was intended to add color along highways and control erosion. But the beautiful and tenacious shrub spread fast and far. By 1860 Virginia declared the plant an invasive species, though it was still widely used in the United States throughout the 1900s. Today, Scotch broom is listed as a Class B noxious weed in Washington, and it is prohibited to buy, sell, or distribute any part of the plant.

Five reasons Scotch broom Is a problem:

  1. Dense: It grows thick and can quickly shade out and outcompete native plants and saplings.
  2. Drought tolerant: Its long taproot allows it to survive periods of drought that many of our native species cannot tolerate.
  3. Fire hazard: It burns easily and can spread fires to the tree canopy. Scotch broom grows near highways, where accidents or hot cars can start fires.
  4. Toxic: It can be deadly to grazing animals such as cows, horses, and elk.
  5. Bad chemistry: Scotch broom alters the soil chemistry, making it difficult for native plants to survive even after its removal.

Scotch broom removal is some of the most costly invasive plant work in the state, incurring over $140 million annually. Most techniques for removal do not work. Manual removal is effective at eradicating individual plants but disturbs the soil, causing nearby seeds to sprout and grow. Plowing and tilling typically miss much of the plant’s roots, allowing it to grow back. The disturbance can also encourage seed germination. If you carefully remove plants individually, over time you can wear out the plant’s seedbank. However, Scotch broom seeds remain viable for over 80 years and therefore require considerable resources and long-term management to control.

Scotch broom piled up at the Schibig-Lakeview Nature Preserve

Working together to remove Scotch broom at Schibig-Lakeview Nature Preserve

In the quiet open space of Schibig-Lakeview Nature Preserve stands Washington’s only native oak species, the Oregon white oak, also known as Garry oak (Quercus garryana). Garry oak savannahs and prairies in the southern Puget Sound area host a diverse array of wildlife species, including many migratory birds. Scotch broom poses one of the most serious threats to this rare ecosystem.

Thanks to the support of hundreds of volunteers, Forterra has successfully managed Scotch broom on the preserve for 20 years. Volunteers, including a local high school Green Team, carefully and tediously remove Scotch broom from the site. Manual removal is labor intensive, but effective if done consistently over a long period of time to wear out the seed bank. Spot-treatment herbicide also is used to remove the plant when other methods are ineffective.

Together, we can remove Scotch broom and restore the rare, beautiful prairies of Washington.
Volunteers removing Scotch broom from the Preserve in 2010

Looking ahead: restoring oak prairies

Once Scotch broom, or any invasive plant species, is removed, it’s important to re-establish native plants in the area. With support from Westland Distillery, Forterra has worked with volunteers to plant over 600 Garry oak trees on the Schibig-Lakeview Nature Preserve. Volunteers have also planted and maintained a diverse set of prairie flora.

The Forterra team recently celebrated success when western bluebirds were spotted on the Schibig-Lakeview Nature Preserve for the first time in over two decades.

In the coming years, Scotch broom will continue to be removed and replaced with native Puget lowland species, such as blue wild rye (Elymus glaucus), yarrow (Achillea millefolium), and shooting-star (Dodecatheon hendersonii), to improve habitat for pollinators that face habitat loss and are imperative to maintaining ecosystem function.

What can you do about Scotch broom?

Scotch broom management is long term and resource-intensive but crucial to protecting and maintaining some of Washington’s rarest ecosystems. Success at the Schibig-Lakeview Nature Preserve attests to the effectiveness of community engagement and stewardship. If you’re interested in volunteering with Forterra, email volunteer@forterra.org.

Have you seen Scotch broom in your area? The Washington Invasive Species Council invites you to report sightings of Scotch broom and other invasive flora and fauna.