Large crabgrass

About

A summer annual grass and one of the most common lawn weeds in the country. It fills thin, sunny spots in summer, then dies at the first frost and leaves bare patches where next year's seeds sprout.

Also called hairy crabgrass, crabgrass

How to identify it

Look for

Pale green clumps with sprawling stems that often turn purplish and can root at the lower joints. Leaves and sheaths carry long, stiff hairs on both sides, and the collar has a thin membrane (ligule) but no ear-like auricles. Seedheads are a few slender, finger-like spikes at the stem tip.

Look-alikes

Smooth crabgrass is smaller with nearly hairless leaves. Bermudagrass has similar finger-like seedheads, but its spikes fan out from a single point and it is a creeping perennial with a ring of white hairs at the collar.

Where it grows

Sunny, thin lawns, garden beds, sidewalk cracks and any bare or disturbed soil.

When

Sprouts from early spring into summer once the top inch of soil stays around 55 to 58 degrees F, flowers from midsummer into fall, and dies at the first frost.

How it spreads

Spreads by seed: one plant can make 100,000 to 150,000 seeds that last at least 3 years in soil, and low stems can also root where they touch the ground.

Most common in

What to do, gentlest first

Start at the top. Weed killers are a last step; always read and follow the label.

1. Mow high and keep the lawn thick Prevent

   Mow cool-season lawns about 3 inches tall and water deeply but not often. A dense lawn shades the soil, so crabgrass seeds can't sprout.

2. Pull or hoe young plants before they seed By hand

   Pull or hoe small plants in beds and lawns in late spring and early summer, before seedheads form. Small patches come out easily by hand.

   Bag plants that already have seedheads instead of composting them.

3. Mulch garden beds Barrier

   Spread 2 to 6 inches of wood chips or compost, or landscape fabric under mulch, in beds. It blocks the light crabgrass seeds need to sprout.

4. Corn gluten meal before seeds sprout Organic spray

   In early spring, 3 to 5 weeks before crabgrass sprouts, spread corn gluten meal (about 20 pounds per 1,000 square feet) and water it in lightly. It only stops sprouting seeds, and control improves over several years.

   Don't use it where you plan to sow seed. Soap-based organic sprays only burn back the tops of young plants.

5. Spring pre-emergent, or spot-treat young plants Conventional spray

   Before soil warms to about 55 degrees F, apply a pre-emergent such as prodiamine, dithiopyr or pendimethalin and water it in. For young plants in lawns, quinclorac or mesotrione work best before plants spread out.

   Read and follow the label. Many lawn herbicides kill garden plants, so keep spray and drift off beds and vegetables. Most pre-emergents also stop grass seed you sow, so skip them where you are reseeding.

Uses, wildlife and pets

Pets

Not listed as toxic to dogs, cats or horses by the ASPCA.