The changing weather at this time of year is something we often welcome. However, rain and warm temperatures also welcome the start of crabgrass season. Crabgrass has earned its name because in summer, the dense mat of low-growing grass resembles the shape of a crab. By August, un-mowed crabgrass can begin to reach upward with claw-like seed heads.
Crabgrass produces seeds from midsummer until frost. The spreading mat of coarse blades produces finger-like panicles in summer. As the seed-carrying panicles mature, they become purple-tinged. Mowing these seed heads short doesn’t stop crabgrass, as plants just ½-inch tall still produce seed.
Crabgrass seeds remain inert for a short period after maturity and dormant throughout the cold winter. However, the seeds are viable for years. When soil temperatures are in a range of 59 to 65 degrees, the seeds sprout and continue the lifecycle. Penn State University research shows that crabgrass seeds usually stop sprouting after July.
Because a single crabgrass plant sheds up to 150,000 seeds, controlling the seeds before they sprout is preferential to hand-weeding multiple plants or applying repeat treatments of post emergent herbicides. Use a pre-emergent herbicide in spring, before soil temperatures rise to 60 degrees. Although crabgrass does not emerge in early spring, RIGHT NOW is the best time to control it. It can be controlled with an application of pre-emergent herbicide. This will reduce crabgrass germination by about 80-90% in your lawn, but the best defense against crabgrass is to keep your lawn thick and healthy so it can’t compete.
It’s important to keep in mind that pre-emergence crabgrass control products cannot be used if over seeding is planned for the spring, since the herbicide will inhibit germination of the desirable grass as well as the crabgrass. (The length of time that must elapse from pre-emergent herbicide application to seeding varies according to the product selected – the label will have the details).
Enjoy your spring, but if you don’t want to become crabby in early summer, make sure either you or a trained professional lawn care service put down your crabgrass control!