When my bright yellow flowers are done,
The process of spreading has only just begun.
These black seed pods split open when dried,
Spreading this invasive far and wide!
This noxious invasive is a common sight along the Sea to Sky Highway. Scotch Broom (Cytisus scoparius) coats the landscape in a sea of yellow in early summer; by fall these plants are covered in hundreds of green to black pea-like pods that split open to spread their seeds.
The story of how Scotch Broom was introduced to North America really goes to show the impact that one person can make. In 1850, Captain Walter Grant planted three Scotch Broom seeds in his garden on Vancouver Island as an ornamental. Nearly 175 years later, the species is commonly found all over Vancouver Island, the Lower Mainland, and up into the Sea to Sky!
Native to Scotland, this perennial shrub is an aggressive spreader in the Sea to Sky region. Scotch Broom is excellent at spreading, as a single plant can produce up to 3,500 seed pods, each holding up to 12 seeds. That’s up to 42,000 seeds per plant (yay, math)! This invasive has ‘explosive’ seed pods that, once dry, split open and launch their seeds into the surrounding area. If that wasn’t already enough, the seeds can survive in the soil for up to 60 years!
Scotch Broom is recognizable this time of year by its green, ridged, woody stems 1-3 m tall and its hundreds of flat, fuzzy seed pods. As the pods dry out, they go from green to brown and then to black right before they split open and shoot their seeds up to 6 metres away. By fall, Scotch Broom has dropped its small leaves, leaving small ridged leaf scars up and down the stems.
Scotch Broom is a threat to natural areas in many ways. It forms extremely dense thickets that both limit animal movement and crowd out other plant species, which reduces the biodiversity of our local areas. Scotch Broom also disrupts the natural food chain by altering the nitrogen composition of the soil and altering which plants can grow in the area. Only to make matters worse, Scotch Broom is highly flammable: the woody stems contain an oily, resinous sap that readily fuels wildfires. Definitely not helpful during fire season!
Without Scotch Broom’s small yellow flowers, it is easily confused with fellow invasive Spanish Broom (Spartium junceum). These species are closely related, with Spanish Broom appearing as a bigger version of Scotch Broom. Spanish Broom typically grows 2 – 4m tall, while Scotch Broom grows 1 – 3m tall. Spanish Broom’s seed pods are also much bigger than Scotch Broom’s, growing 4 – 10cm long as compared to 2.5 – 4cm. (Note: there have been no reported sightings of Spanish Broom in the Sea to Sky thus far, so be sure to report it if you see it!)
Per SSISC’s Invasive Plants Priority List, Scotch Broom is listed as a species to contain in Squamish and eradicate in Whistler and Pemberton. We rely heavily on reports from the public to understand the current distribution of plants in the Sea to Sky and prevent their spread. With that in mind, we invite you to keep your eyes peeled for Scotch Broom and report any sightings.