- Cytisus scoparius
Scotch broom (Cytisus scoparius) is an escaped garden ornamental, common west of the Coast-Cascade Mountains in southwest BC, and is concentrated at the southern end of Vancouver Island. It has also been reported on the Queen Charlotte Islands as well as in parts of the Kootenays and North Okanagan–Shuswap areas.
Scotch broom is an evergreen shrub, with bright yellow, pea-like flowers that may have red markings in the middle. Stems are woody and 5-angled, with lower, stalky leaves composed of 3 leaflets and upper, un-stalked leaves. Flat, hairy seedpods are initially green, turning brown or black with maturity. Scotch broom grows to 1-3 metres in height at maturity.
Scotch broom spreads by seed and lateral bud growth, and mature plants can produce up to 3500 pods, each containing 5-12 seeds. As seedpods dry they split and spiral, expelling the contained seeds up to 5 metres. The plant can also spread to new disturbed areas through seed transport by vehicles and machinery. Photosynthetic stems also enable year-round growth.
Due to its affinity for light-dominated, disturbed areas, any disturbance activity, such as road or home construction near infested areas, can enhance spread. Scotch broom invades rangelands, replacing forage plants, and is a serious competitor to conifer seedlings; Douglas fir plantation failures in Oregon and Washington have been credited to infestations of this plant.
Dense thickets can:
- increase wildfire fuel loads, thereby escalating wildfire intensity;
- obstruct site lines on roads, resulting in increased maintenance costs for removal;
- limit movement of large animals; and
- displace native plant species.
A few native and ornamental alternatives to plant instead of Scotch broom include: Prickly Rose; Shrubby Cinquefoil; Forsythia; Deciduous Yellow Azalea; and Japanese Kerria. Read more about these alternatives in the Grow Me Instead booklet for BC.