Since then, Scotch broom has invaded much of the Paciﬁc Northwest; its range stretches from British Columbia
A woody, leguminous shrub, Scotch broom establishes quickly in disturbed areas, often outcompeting native plants to form dense, monospecific stands (Figure 1). Scotch broom’s economic impact can be significant; the state of Oregon loses more than $40 million annually in timber revenue and control expenses.
Identification and Biology
Scotch broom is a woody shrub that can grow to 10 feet tall, although the average plant is usually 3 to 5 feet. Plants have sharply angled branches and bright yellow flowers. Plants bloom between March and June, before leaves emerge. Young branches have five ridges, are green and hairy, and are responsible for about half of the plant’s photosynthetic activity.
Branches become smooth and brown as they age. Leaves are small and oblong, often with three leaflets, and develop later in the growing season.Single or paired flowers, clustered in leaf axils, are bright yellow and typical of plants in the Fabaceae family (Figures 2, 3 and 4, page 2). Occasionally plants bearing maroon flowers or bicolor maroon and yellow flower petals are in Scotch broom populations (Figure 5, page 3).
Andrew Hulting, Extension weed specialist; Karin Neff, faculty research assistant; Larry Burrill, former Extension weed specialist; all of Oregon State University; Eric Coombs, entomologist, and Glenn Miller, integrated weed management specialist, both of Oregon Department of Agriculture; Robert Parker, Extension weed scientist, Washington State University.
A Pacific Northwest Extension publication
Oregon State University • University of Idaho • Washington State University