Though sometimes attractive in the landscape, the scotch broom shrub (Cytisus scoparius) is a noxious weed in the Northwestern U.S. and responsible for the loss of a good deal of that areas’ timber income due to crowding out native species. Scotch broom control is difficult and often time-consuming, but worth the effort to get rid of scotch broom in the yard and forest.
Scotch broom shrub was introduced as a landscape ornamental as early as the 1800’s, then used extensively for erosion control in public landscapes, such as roadside plantings, but quickly became a nuisance. Once established, it is difficult to kill scotch broom.
Scotch Boom Identification
Scotch boom has tear-shaped leaves that grow in groups of three and mostly bright yellow flowers with occasional purple and red flowers mixed in. The flowers grow in clusters along the length of the stems. When in flower, the entire bush appears to be yellow.
After flowering, scotch broom will produce several dozen large pods that contain hard brown seeds.
Reasons to Kill Scotch Broom
Effects of scotch broom shrub include competition with native forest plants. In addition, the scotch broom shrub produces soil conditions which encourage growth of other non-native weeds, choking out native foliage.
Wildlife find the shrub unpalatable and may be driven from a habitat overtaken by the scotch broom. Preserving native habitats is an important reason to get rid of scotch broom.
Information on Scotch Broom Control
Scotch broom control may be mechanical, shearing to the ground by hand or with machinery. Mechanical scotch broom control requires repeated shearing with a chainsaw or trimmer. The roots form a dense and returning mass so this may have to be done repeatedly to kill the plant.
Root removal is often best carefully done by hand in the home landscape. Make sure you get all of the roots, as partial removal of roots will it to come back instead of fully getting rid of scotch broom.
Controlling scotch broom in the home landscape may be best accomplished by continual shearing during the driest seasons. Be mindful of new sprouts, which will quickly establish themselves and remove these as they appear.
Spread mainly by prolific seed production and dispersal, it is difficult to kill scotch broom in the long term because of the seeds. The hard-coated seeds remain viable for as long as 80 years.
Mechanical removal with large tillers and plows often does not work well with controlling scotch broom, and encourages re-growth. Scotch broom shrubs most often overtake areas where soil had been disturbed, as by tilling. Broad spectrum herbicide control is somewhat successful, but must be applied before flowers emerge.
Biological controls, such as a species of seed weevil, are under experimentation and found to be successful at reducing seed spread in Oregon. Larvae of the weevil enter seedpods and are estimated to eat 80% of the seed before they can disperse. Check inside seed pods before treating with chemicals. Larvae should not be destroyed, as they appear to be the best resource for controlling scotch broom invasions.