Crabgrass: A seedy invader of thin lawns
Characteristics of Crabgrass
Although you might find this grassy weed growing under shrubs, around flowers and in the vegetable garden, crabgrass (Digitaria sanguinalis) is most infamous as a lawn invader. Crabgrass plagues lawns throughout the United States and beyond, usually elbowing its way into weak, thin lawns that are struggling to grow in poor or compacted soil.
Identify crabgrass by its long, wiry stems and ground-hugging habit. Grassy leaf blades fan out along the stems. It often roots at the leaf joints. Crabgrass is a highly effective and rampant seeder; an individual plant may produce upwards of 100,000 seeds. Once it finds a lawn, it can quickly dominate turfgrass.
Young crabgrass seedlings germinate from mid-spring through late summer and quickly send out bladed tentacles across the lawn surface. By late summer, flower and seed stems that look like small wheat stalks develop. The fleck-sized seeds mature, turn brown and drop to the surface. There, they await spring when they’ll germinate and start the next cycle.
This European weed is not cold-hardy. In much of the United States the parent plants will die off with hard frost, leaving plenty of dropped seed behind. This makes crabgrass vulnerable to weed preventer.
Getting Rid of Crabgrass
Crabgrass is an annual weed, shallow-rooted and easy to pull. Hand pulling is very effective if the infestation is light and plants are removed before they set seed. Crabgrass grows best in full-sun, so mowing the lawn high at 3 or 4 inches can discourage growth. A dense healthy lawn, overseeded in fall, will minimize crabgrass problems in the spring.
Apply Preen Lawn Crabgrass Preventer in early spring to stop crabgrass germination for up to 4 months. Preen Lawn Crabgrass Preventer will also kill crabgrass seedlings up to 4 weeks old. Timing is important. One good indicator is to apply preventatives when forsythia is in peak bloom. During cool, damp summers, crabgrass may continue germinating beyond 4 months, so a second treatment may be needed for later-season control. Always read and follow the label directions.