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When should I treat my lawn for crabgrass?

Wednesday - 3/17/2010, 5:00am  ET

By Caitlin Hillyard
Special to

WASHINGTON - Spring means weeds are getting ready to attack your lawn.

Gray from Springfield asked WTOP when he should treat his lawn for crabgrass and other weeds.

Garden Guru Mike McGrath says you can't mark a date on your calendar. The best time to treat a lawn is different every year. In years with heavy snow, like this year, crabgrass will sprout later.

But there is a way to plan when to treat your lawn. Certain plants will let you know when the time is right.

"Crabgrass seed germinates at a soil temperature of 55 degrees, which luckily is about the same time that forsythia and redbuds first begin to bloom," McGrath says.

When you see the flowers, treat your lawn. Forsythia blossoms are yellow and redbuds are pinkish-red.

You don't have use chemicals, McGrath says.

Corn gluten meal will keep crabgrass away and fertilize your lawn. It's a byproduct of manufactured cornstarch that's high in protein and nitrogen.

"All crabgrass died over the winter, but before it died it dropped a ton of seed. That seed is waiting to sprout right now, as soon as the soil temperature gets warm enough," McGrath says. "That's why people use pre-emergent herbicides. They want to prevent the weed from emerging, from sprouting successfully."

Corn gluten won't hurt your lawn because your grass doesn't germinate in the spring. It also won't harm the environment.

The best time to put down corn gluten is before it rains, especially if a dry spell will follow. The gluten gets wet and then dries, which forces the seeds to destroy themselves at the fastest possible rate.

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