Diagnose the Lawn Problem
Figure out why you need to repair your lawn. If you don’t determine the problem, fixing your lawn could be a waste of time. For example, if grubs are the problem, you’ll need to treat for them before laying a new lawn. But if too much shade is the problem, you’re better off forgetting a lawn and investing in low-maintenance shade-loving ground covers instead.
Learn even more about growing the best lawn you can.
Give Your Lawn a Fresh Start
If more than half of your lawn is screaming for help, start from scratch. Spray the lawn with an herbicide containing glyphosate (be sure to follow all directions on the packaging). It kills all vegetation but allows new turf to re-establish quickly.
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Mow the Lawn Low
Wait a couple of weeks after applying the herbicide, then mow the turf as short as you can. It may seem counter-intuitive to really scalp it as you repair a lawn, but this low mowing leaves the area with short, dead plants, to prevent erosion, and keeps the dead plants from shading your new lawn too much.
read more at Better Homes & Gardens