Crabgrass

Crabgrass is an annual weed and therefore reproduces by seed. The best way to control crabgrass is with a preemergent herbicide. Once crabgrass gets established, it is very hard to control with post emergent herbicides.

What about the timing of preemergent herbicides? In SE Michigan, we are right in the middle of the window to get effective control with preemergent herbicides. Soil temperatures of 50-60 degrees F are optimal for germination and that usually occurs in April. Your lawn care company has no doubt been out already or at least they have sent out a reminder.

Once the herbicide has been applied (in most cases it is impregnated on a fertilizer carrier) it should be irrigated, at  least enough to get it in contact with the soil surface. You should not aerate after application as this breaks the barrier that is formed by the herbicide.

Another method to control crabgrass ... or any other weed, is to promote a healthy and dense lawn so that the grass is more competitive. You can do this by having a reasonable mowing height, like 2.5 - 3 inches and fertilizing at an annual rate of 2-3 pounds of Nitrogen/1,000 square feet. These Nitrogen applications should be avoided during the summer months and saved for September through November. Spring applications are OK, but no more than 1/3 of the total annual Nitrogen used should be applied in the spring.

If you do see crabgrass mid-summer or later, my advice is to leave it. It will die with the first solid frost and then you can control any new plants the following spring.