Carpet burweed (Soliva sessilis) is an invasive plant that spreads easily and aggressively in open natural areas, as well as in lawns, golf courses, RV parks, and tent sites. Each tiny carpet burweed plant produces up to 200 seeds with sharp, spiny tips. The spines enable the plant to disperse its seeds. The spines can pierce and lodge into tents, tarps, equipment, tires, shoes, paws, fur, and other objects and inadvertently be carried to new locations, sometimes at considerable distances.
Carpet burweed is a winter annual. Seeds begin to germinate with the autumn rains, and continue germinating throughout the spring. By early spring the plants start to form a lush green carpet. Seeds are produced in spring and summer, and the plants die back during the summer drought. Seeds can remain viable in the seed bank for up to 20 years.
Once burweed gains a foothold, it starts to outcompete the other vegetation. Its early germination and carpet-forming habit in early spring excludes plants that are just beginning to grow at that time of year. When burweed dies back in the late summer, it creates bare patches that are ideal for its own occupation the following year. The species poses a serious threat to Garry oak, rock outcrop, coastal bluff, and other open, sensitive ecosystems in the region.
The spines on carpet burweed seeds can readily and painfully pierce the skin of humans and animals, sometimes leading to infections. The large brown patches left after burweed dies back in late summer are also detrimental to the aesthetic and recreational values of picnic areas campgrounds, and other sites with intensive human use.
Where Carpet Burweed is Found
Carpet Burweed is native to South America and has since spread to many parts of the world. The known range in Canada is primarily southern and southeastern Vancouver Island and the Gulf Islands. Carpet burweed has been found in Garry oak and associated ecosystems, particularly in areas with heavy use.
How Carpet Burweed is Being Treated
Beacon Hill Park treatments include spot burning burweed plants with a propane “tiger” torch where infestations are thick, hand-pulling of more scattered burweed plants, and sowing grass seeds. To prevent seed dispersal, burweed patches in the parks have been fenced. However, as an invasive species, it can be difficult to fully eradicate and ongoing management efforts will be required to prevent its continued spread.