The good thing about Vinca minor, or periwinkle, is that it’s a great groundcover, growing quickly to fill in problem areas. These plants even thrive in shady spots with lousy soil, and serve well for erosion control. The bad part is that periwinkles spread beyond their intended boundaries. Vinca quickly rages out of control, even encroaching into forested areas where it crowds out and displaces native plants. Then comes the ugly part--it's difficult if not impossible to eradicate. Gardeners are typically instructed by retailers and extension services to destroy the noxious weed by killing the roots with potent herbicides. If this doesn’t appeal to you, try the old-fashioned approach: time, effort, patience and persistence. Although challenging and time consuming, you can kill those invasive periwinkles without the use of dangerous chemicals.
Dig and pull up all the Vinca that you can by hand. Rake up and destroy all parts of this noxious weed. Don’t leave any of it lying around because these plants root readily from cuttings. You already know that any roots left unattended will sprout up, too. Don’t add Vinca to your compost heap.
Mow or cut remaining plants as close to ground level as possible.
Add 2 oz. liquid hand dishwashing liquid to a gallon of white vinegar. Stir slowly to avoid creating excessive bubbles. Pour into a garden sprayer and apply generously to the cut Vinca plants. The vinegar may not kill the weeds, but it will weaken them. Don’t expose desirable plants to the solution, which kills indiscriminately.
Flood the soil of the affected area with the vinegar solution.
Cut large empty cardboard boxes down into sheets. Cover the Vinca-infested area with cardboard, overlapping the ends of the sheets. If possible, extend the cardboard several feet beyond the perimeter of the affected area to completely deprive the weeds of light. Soak the cardboard with the garden hose.
Pile 6 to 8 inches of compost or shredded mulch on top of the cardboard and walk on it to pack it tightly. Drench it thoroughly with water. This barrier will reduce the weed’s vigor and inhibit growth as it struggles to reach the light.
Pull stray runners that attempt to emerge from beneath the barrier. Keep it packed and heavy with water at all times.
Soak the mulch and cardboard barrier with white vinegar once weekly thereafter and continue to keep it wet until periwinkle shoots stop sprouting up from underneath.