Mowing short will stress the grass...as will heavy raking. My suggestion: skip two mowings--let the crabgrass get tall and luxurious; then AMBUSH! Surprise it by cutting at 1/2 inch. Rake or bag as much crabgrass as you reasonably can--don't worry about the roots; frost kills them. Crabgrass is a hot weather annual. Apply your seed when the weather is still hot. Then its a battle between your new grass and whatever remains of the crabgrass. However, the crabgrass stops growing when the nighttime temps fall to about 45. The new grass then begins to take over. Stimulate it with fertilizer about this time. Get it to grow as fast as you can...the idea is to get as much growth and density as you can before the weather stops further growth in the fall. Crab disappears. Growth of the new grass stops when the day temps fall below 45 or the night temps fall below 32. In Michigan, that happens about mid November. Away from Lake Michigan, it will be a few degrees colder.
Last edited by RigglePLC; 07-28-2013 at 03:48 PM.