How to - Pests & Diseases

The top five most invasive plants in Canada

Canadian Gardening magazine’s TransCanada columnists identify the biggest eco-bullies across the country

Many aggressive exotics are invading our natural landscape, out-competing wildlife habitat and native plants. Here are the plants that should have you reaching for your gardening gloves and whatever weeding tool you have available.

British Columbia
Himalayan blackberry (Rubus armeniacus, above) is the Dr. Jekyll and Mr. Hyde of invasive plants in more temperate areas, such as Vancouver and the Gulf Islands, Lower Mainland, Sunshine Coast, the Okanagan and West Kootenays. Its merits are abundant berries, popular for homemade jams and pies, which is why it was brought here from India by American botanist Luther Burbank; but the dark side is an aggressive, thicket-forming alien species that smothers indigenous plants. Unfortunately, it has run amok through wildlife seed dispersal and rampant tip-layering (when the ends of young canes develop roots where they touch the ground, producing new plants). —Mike Lascelle

Prairies
Salt-cedar (Tamarix ramosissima) is a hardy shrub with arching branches and dense clusters of pink, late-summer flowers. Found in wetlands, it draws salt from the air, depositing it into the soil, killing native plants.  —Alison Beck

Ontario
Dog strangling vine (Vincetoxicum rossicum and V. nigrum) is a tenacious perennial invading natural areas of southern Ontario. The stems, up to two metres long, twine together, forming rope-like tentacles that climb through and smother other plants. Leaves are ovate with smooth edges, while pink to maroon flowers appear in spring. Seed pods are similar to those of milkweed. —David Hobson

Quebec
Common reed (Phragmites australis) is a tall marsh grass with feathery flowerheads. It spreads by creeping rhizomes, choking out neighbouring plants and blocking drainage ditches. This is the aggressive Eurasian strain, not the more sedate North American clone. —Larry Hodgson

Atlantic
Couch grass a.k.a. quack grass (Elytrigia repens) This perennial grows in clumps and bears dense, green, linear leaves. Spreading by distinctive, white rhizomes, it’s extremely invasive—quickly rebounding after rototilling (each section of chopped rhizome sprouts a new plant). It also creeps under mulch and entangles itself in perennials. —Sandra Phinney

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  • Page 1: Aggressive plants

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