CORVALLIS, Ore. — Himalayan blackberry has become one of the Pacific Northwest’s most invasive weeds, spreading rapidly from Northern California to British Columbia. A single plant can grow into a six-square-yard thicket in less than two years, crowding out native vegetation and desirable landscape plants.
“Blackberry canes can produce hundreds of berries, each full of seeds. Birds and animals feed on the berries and spread the seeds over long distances.”
“Blackberries keep popping up because of their tremendous and effective dispersal potential,” said Brooke Edmunds, horticulturist with the Oregon State University Extension Service. “Blackberry canes can produce hundreds of berries, each full of seeds. Birds and animals feed on the berries and spread the seeds over long distances. Even banana slugs help by eating the berries and dispersing the seeds.”
With persistence and good timing, even large blackberry patches can be brought under control. Physical removal is the most effective long-term strategy, Edmunds said.
Dig up canes or plow under thickets to remove existing plants — but be aware that this also creates an ideal seedbed for new seedlings. Replanting the area with hardy perennials, such as grasses, can help outcompete emerging blackberry shoots and prevent regrowth.
If digging isn’t possible, consider mechanical mowing or grazing with goats. Both methods weaken plants by repeatedly removing leaves, which starves the roots by cutting off the plant’s food supply. However, both require repeated effort and can damage surrounding vegetation.
“Goats tend to graze only around the edges of a patch,” Edmunds said. “People sometimes mow paths, lay boards or flatten canes so goats can reach the center of the thicket.”
Using herbicides carefully
Herbicides can also be effective if used correctly. Multiple products are available for residential and commercial use throughout the year, but always check the product label for rates, timing and application restrictions.
For home landscapes, consult OSU Extension’s Solve Pest Problems website for step-by-step blackberry control guidance. Professional applicators can find detailed information in the Control of Problem Weeds chapter of the Pacific Northwest Weed Management Handbook.
Contrary to popular belief, cutting plants before applying herbicide is usually not recommended unless they are too large to reach with spray equipment. Cutting reduces leaf area and limits how much herbicide is absorbed, making treatments less effective.
Don’t walk away after treatment
No matter which control method you use — digging, mowing or spraying — follow-up maintenance is essential.
“You can’t treat a patch of blackberry and then walk away,” Edmunds said. “Eradicating a large infestation can take several years. Don’t take a break and let the blackberries regain their strength. Check the area each year and remove new seedlings before they spread.”
After successful removal, replant the area with vigorous, competitive plants that will shade out or crowd potential regrowth. Consistent attention is the key to keeping Himalayan blackberry under control for good.
Previously titled Methods to control blackberry thickets
