Everything You Didn’t Want To Know About Scotch Broom

Landowners can set up a meeting to pick up a weed wrench by calling us at 253-798-7263.”

While driving along the peninsula as the seasonal temperature increases, some may notice an unruly sight.

Scotch broom, Cytisus scoparius, a Class B noxious weed according to the Washington State Noxious Weed Control Board, finds its home near any grassland or open forests.

In Washington, these noxious weeds are rated Class A to Class C. While Class A designates a weed as nonnative with limited distribution within the state, Class B designates it as widespread within certain parts of the state, and Class C implies it is widespread throughout Washington, with a significant impact on agriculture.

Scotch broom is also a weed listed on the Washington state quarantine list, prohibiting its sale, purchase, transfer, or distribution of seeds, per WAC 16-752.

But what is scotch broom, and how did it end up here?

Native to Europe and islands off Africa, scotch broom was brought to Washington in the 1800s. It was first mentioned in the Seattle Post-Intelligencer in January 1877, as part of a bouquet gathered by a Mr. Lawton of the Seattle Nursery, “all growing on New Year’s Day in an open garden.”

By 1929, it was described by Lyman Benson as “widely naturalized in the prairie and cut-over country,” while studying a sample of it in Thurston County. Known for its bright yellow flowers, it was originally brought for its use as an ornamental plant, but has adapted to many other uses.

Scotch broom began to be used to prevent erosion, being planted near roads, in medians, and on hillsides to prevent damage to roadways. A mistake with good intentions, however, quickly became widespread.

Due to scotch broom’s high seed count, averaging just under 10,000 seeds spread per plant per year, its ability to quickly spread was soon noticeable. Scotch broom seeds are unusually tough and durable, meaning that the likelihood of a seed being destroyed due to predation or other factors is minimal. The hard shell-like coating around the seed is estimated to keep it viable for five to 20 years, with some researchers suggesting that a seed may still be able to sprout after 80 years. This toughness, along with scotch broom’s ability to release seeds up to 16 feet away, is what allows it to spread so effectively. Not only does this rapid reproduction create an eyesore, it also causes harm to native plants and livestock.

As scotch broom makes its way into a newly developed or low-lying forest, it steals water, nutrients, and sunlight from native species such as Douglas-fir saplings. According to the Washington State Noxious Weed Control Board, a study found that scotch broom may “occupy as much as 90% canopy cover and intercept 65% of the intermittent light,” meaning that something like a working forest or recovering habitat after a forest fire may have no chance to return.

Scotch broom also depletes nutrients in the soil for native species and is toxic to livestock, especially horses, and causes neurological dysfunctions and digestive problems. If ingested over a longer period, problems for the offspring of livestock may also appear.

But these problems do not apply to goats, which may be used as a potential broom control method.

Other methods for eradication include cutting the base in late summer/early fall when the plants are more likely to be experiencing drought, depriving the plant of nutrients, or using heavy machinery to dig them up.

Although brush burning by itself is not effective, repeat burning over the area followed by the planting of native plants might be. The most effective method is pulling scotch broom out by the roots and monitoring the area for new growth. While repetitive pulling over the course of several years in the affected area may be necessary, it ensures that it will not continue to grow back.

In an email to KP News, Haley Thompson, a community program educator with the Pierce County Noxious Weed Control Board, listed local resources available for KP residents, primarily the Weed Wrench Loan Program.

“Landowners can set up a meeting to pick up a weed wrench by calling us at 253-798-7263,” he said. “Landowners will have to pay a deposit of $25.00, which will be refunded upon the return of the weed wrench in good condition and within the time frame allotted. Weed wrenches can be loaned out for up to two weeks from the day that it is checked out.”

When disposing of broom, small amounts of woody debris can be placed in county compost bins as yard waste. Any debris with seed pods must be disposed of via a county transfer station, such as the one south of Key Center.

General information regarding scotch broom can be found at https://www.nwcb.wa.gov/weeds/scotch-broom.

Questions regarding Washington’s quarantine list can be sent to the Washington State Department of Agriculture at plantservices@agr.wa.gov.