Scotch Broom is an upright shrub with slender green
branches sprinkled with small, bright green leaves. Highlighted by profuse
yellow-gold flowers, this shrub puts on a fantastic display during late spring
and early summer. Drought-tolerant and thriving in poor soils, it is perfect
for that sunny spot in your yard!
Tempted to add this shrub to your spring planting
Beware: despite the tantalizing description and easy care, you will be inviting
in one of the worst noxious weeds in the West.
Scotch or Scot’s broom, Cytisus
scoparius, is a member of
the Legume family (Fabaceae). Native to Europe and North Africa, it has become
naturalized across US. First introduced on the west coast as an ornamental and
used extensively as a roadside plant, Scotch broom has become a familiar sight
in western Washington.
Why is it a problem?
Scotch broom lights up the roadside in spring, it
is not a welcome sight for land managers. It quickly forms very dense stands
and can spread from disturbed areas into more natural vegetation. The qualities
that make this plant a successful colonizer put it in direct competition with
native plants, which often lose out in the battle for space and resources.
rapidly and fixes nitrogen which allows it to
thrive on very poor soils. It is also a prolific seed producer (up to 12,000
seeds from a mature plant) and the seeds remain viable in soil for at least
five years. Its large size, the formation of copious seeds and its ability to
resprout after cutting makes control of Scotch broom very labor intensive.
covers more than 700,000 acres in parts of
California. Locally, Scotch broom is a particular problem in South Puget Sound
prairies, a plant community adapted to nutrient-poor soils. Several rare plants
and animals such as golden paintbrush (Castilleja levisecta) and the butterfly
Mardon skipper (Polites mardon) depend on this prairie community. Scotch
broom’s encroachment on these prairies is interfering with the establishment of
native plants and threatens this ecosystem.
Although it is often associated with allergies,
broom is not responsible. Dr. Charlie Reed, formerly professor emeritus at the
Mayo Clinic who worked on allergens in the 1950s stated that the pollen of
Scotch broom was not an allergen. Other sources state that the pollen of Scotch
broom is too heavy and does not become airborne, unlike the alder and grass
pollen that are probably the main offenders.
Scotch broom is a Class B noxious weed
State. Although it is widespread in western Washington, it has not spread into
eastern Washington. Prevention of seed production is required by law in
counties of eastern Washington in an attempt to control its spread there.
Scotch broom, unfortunately, is still available in nurseries in many states and
over the web, although it is regulated by WSDA and it is illegal to buy, sell
or offer Cytisus scoparius for sale in Washington. For more information on
brooms visit: http://dnr.metrokc.gov/wlr/lands/weeds/index.htm. For questions
contact King County Noxious Weed Control Program at 206-296-0290.