Killing Crabgrass Weeds in the Organic Lawn and Garden

Even those who aren’t sure what crabgrass looks like or whether their lawn is afflicted with it know that these grass weeds are a pestilence in the landscape. In the spring, it’s difficult to miss the crabgrass killer advertisements one hears on the radio and television, a call to arms that gardeners can’t afford to ignore. What can gardeners who eschew chemicals in the lawn and garden do to get rid of crabgrass? The answer is plenty.

Identify Crabgrass

Crabgrass actually refers to a genus of annual plants that encompasses approximately 300 species of grassy weeds. The varieties of crabgrass common to North America can grow as tall as three feet, but the plant is very adaptable and can still form seeds when the mower keeps it short.

Gardeners with thin or struggling lawns can recognize these thugs sending their spreading stem clumps and fingerlike seed spikes growing from summer to fall. The leaf blades may appear bluish or purplish green, and the plants can be smooth or hairy.

Cultural Crabgrass Control

Gardeners who have a minimal crabgrass problem can control it by increasing the vigor of their lawns. A thick, healthy lawn can prevent crabgrass from germinating by shading the seeds. Mowing grass no shorter than 2 to 3 inches strengthens turf grass by providing more plant surface to engage in photosynthesis, and also keeps the sun from triggering growth in weed seeds.

Proper irrigation can influence crabgrass growth in the lawn. Organic gardeners should strive to water the lawn infrequently and deeply, applying one inch of water to the lawn weekly, which encourages deep grass roots.

Applying organic fertilizers to the lawn during the growing season can increase the vigor of the turf grass to the point where it will crowd out the crabgrass. An application of finely screened compost promotes healthy grass at any time during the growing season. Gardeners can put down fish, blood, and bone meal in the early spring and summer to provide slow-release feeding during these peak growing times.

Organic Crabgrass Preventer

Organic gardeners can apply corn meal gluten in the spring and in the fall to stop crabgrass from germinating. This natural corn byproduct stops all seeds from germinating, including turf grass seeds, so gardeners shouldn’t apply it at the same time they are reseeding their lawns.

Crabgrass Control in the Vegetable and Flower Garden

Ornamental beds with inadequate mulch are ripe for an invasion of crabgrass. A 3-inch layer of organic mulch not only suppresses the germination of crabgrass, it makes established weeds easier to pull. Gardeners should dispose of crabgrass weeds rather than placing them in the compost bin, as the seeds can stay viable for up to three years if the bin doesn’t generate enough heat to destroy them.

Source:

University of California Integrated Pest Management Program