Your crabgrass has been killed by frost and the seeds have been deposited in your lawn to germinate next spring when your weather warms up. This time of year it is helpful to ID the dead crabgrass plants so that you know to add crabgrass prevention to your “to do” list for next spring. By next spring these dead plants will be mostly gone so now is the time to have a look around your lawn.
One helpful ID tip is to look closely at dead crabgrass where you will see the shriveled up “fingers” of the seed head. Click picture to enlarge.
This is a crabgrass seed head in August when seeds were being spread over your lawn. Notice the three fingers. These fingers will be less prominent on dead crabgrass this time of year.
One grassy weed that gets confused with crabgrass is Nimblewill. Even though Nimblewill is dead-looking in winter, it actually is still alive. A crabgrass preventer does not prevent this dormant perennial weed from growing back from its roots in spring. Click picture to enlarge.