Smooth crabgrass

About

A low-growing summer annual grass that shows up in thin lawns alongside large crabgrass. It sets seed even when mowed short, then dies at frost and leaves gaps.

Also called crabgrass

How to identify it

Look for

Smaller than large crabgrass and often lies flat. Leaves are smooth, about 1/4 inch wide, with just a few long hairs near the base, and older leaves and sheaths turn reddish purple. Seedheads have 2 to 6 finger-like spikes at the stem tip.

Look-alikes

Large crabgrass is hairy on the leaves and sheaths. Goosegrass also grows flat, but it has a silvery-white center and its stems don't root at the joints.

Where it grows

Thin, sunny lawns, lawn edges, garden beds, cracks in paving and other bare soil.

When

Sprouts from spring into early summer when soil reaches the mid-50s F, flowers and seeds from late summer into fall, and dies at the first frost.

How it spreads

Spreads by seed, even from plants mowed as low as 1/2 inch, and now and then by low stems rooting at the joints.

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 at the right height for your grass (about 3 inches for cool-season lawns), water deeply and less often, and fertilize properly so turf shades out seedlings.

2. Pull young plants before they seed By hand

   Hand-pull or hoe small plants in beds and lawns before seedheads form.

   Bag plants with seedheads instead of composting them.

3. Mulch garden beds Barrier

   Keep 2 to 6 inches of wood chips or compost, or fabric under mulch, on bed soil to block the light seeds need.

4. Corn gluten meal before seeds sprout Organic spray

   Spread corn gluten meal in early spring, 3 to 5 weeks before crabgrass sprouts, and water it in lightly. It won't kill plants that are already up.

   Don't use it where you plan to sow seed.

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

   Apply prodiamine, dithiopyr or pendimethalin before soil reaches about 55 degrees F and water it in. Young plants in lawns can be spot-treated with quinclorac or mesotrione.

   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.

Uses, wildlife and pets

Pets

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