Crabgrass is a warm season annual grass. While it germinates in spring, its most vigorous growth depends on warm summer days.
Crabgrass seeds germinate late winter and early spring when soil temperatures reach 65 degrees Fahrenheit for at least one week.
The best way to rid lawns of crabgrass is to apply a preemergent herbicide. This herbicide creates a barrier in your lawn that prevents crabgrass seeds from germinating.
The time of year to apply a preemergent depends on the weed as well as the weather we’re having. Warmer weather in February and March will accelerate things, while cold, wintry weather will delay weed seed germination. Also, some seeds germinate relatively early while others wait until later when things have warmed up nicely. A good rule of thumb is to apply preemergents when the forsythias are blooming around town.
Don’t rake, aerate or dethatch your lawn after applying crabgrass preemergent. The barrier can be destroyed.
Most preemergents must be lightly watered in immediately after application. A delay of even an hour will reduce the effectiveness of the product.
Know your weeds. A lot of people think they have crabgrass when in reality they have Bermuda grass or a field fescue which are both perennials and won’t be affected by a preemergent.
Something else to remember about crabgrass is that it absolutely will not grow in the shade. If your weed is growing in shade, it’s not crabgrass.
Prevention of crabgrass invasions is best accomplished by having a thick, vigorous lawn. Proper fertilizing schedules and amounts along with the appropriate mowing height will keep crabgrass seed from getting a foothold in your lawn.