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Smooth and Hairy Crabgrass

Lawn Weed Identification and Control

How to identify and manage crabgrass, one of the most common and invasive grass weeds. Pictures are included to help with identification.

Every landscaper, gardener, hobbyist or do-it-yourself homeowner is -- or will be at some point -- very familiar with crabgrass, it grows everywhere, but the good news is it is very easy to prevent.

This weed is a warm-season annual grass, which means it sprouts from seed when temperatures rise in late spring and through the summer and then will die when temperatures cool or with the first hard frost in the fall.

It thrives on moist sites with plenty of sunlight and will invade areas where your lawn is thinnest and along edges and sidewalks - wherever sun hits the ground and there is little competition from lawn grasses. A dense and thick lawn is the best weed preventer.

Crabgrass Control

Annual weeds are easy to control with preemergence herbicides. Timing of application is very important, they need to be applied before weed seeds sprout. Preemergent weed killers work on germinating seeds or seedlings (young plants) that have not developed a root system. They have no effect on established weeds so they have to be applied before seedlings emerge from the soil.

Tip from seasoned gardeners: Forsythia blooms in the spring (a shrub covered with yellow flowers) when the soil temperature reaches 55 F°, and crabgrass will germinate when soil temperatures are above 55 F°; many gardeners use forsythia as a reminder to apply their preemergent herbicide.

Daffodils and flowering dogwood blooms are also good reminders.

Weed Images

Hairy Crabgrass Smooth Crabgrass
Hairy (Digitaria sanguinalis)

USDA-NRCS PLANTS Database / USDA NRCS. Wetland flora: Field office illustrated guide to plant species.
Smooth (Digitaria ischaemum)
USDA-NRCS PLANTS Database / Hitchcock, A.S. (rev. A. Chase). 1950. Manual of the grasses of the United States. USDA Miscellaneous Publication No. 200. Washington, DC.

Crabgrass The seed heads look like fingers at the ends of the seed stalks.
crabgrass Thrives on moist sites with plenty of sunlight. Your best defense is a dense and vigorous lawn.
crabgrass Its spreading growth habit will crowd out lawn grasses.
Crabgrass Grows in areas where your lawn is thinnest and along driveways, curbs and sidewalks.

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