Perennial Garden Weeds
- Herbicides formulated for broadleaf weeds like Canada thistle and plantains also kill broadleaved garden plants. Herbicides for perennial grasses, such as Bermuda grass, damage grassy garden plants and 2,4-dichlorophenoxyacetic acid persists in food crops. Pre-emergent herbicides also kill seeds of self-seeding garden plants like hollyhock.
- Perennial weeds die back to the ground in fall and grow again in spring, so taproots and rhizomes must be removed during fall clean-up and before spring planting. Clemson Cooperative Extension recommends light organic mulches to keep soil cool and deny light to weeds. Regular shallow cultivation throughout the season cuts off leaves, eventually killing the roots. Rototilling is best avoided as it produces more roots and rhizomes.
- Herbicides like glyphosate are effective, but they should be applied when soil is fallow or as weeds enter dormancy. Weed growth slows when other plants shade the soil. Cover crops help to keep the pressure on weeds. Tom Cleere and Steve Nowotarski of the American Dahlia Society recommend rye, buckwheat, clovers and peas to fix nitrogen and crowd out weeds.
