Many lawns in this area are planted with cool-season grasses including Kentucky bluegrass, tall fescue, perennial ryegrass and fine fescues. They typically withstand cold winters, but each summer their growth slows. But a few simple steps can revive them in late summer. Youâll often see lawns planted with these varieties begin to brown out in the summer. This is the time to raise that mower deck, because short mowing heights promote shallow roots, which makes it harder for the plants to access water and nutrients in the soil. Cutting your grass at a height of 3 or 4 inches will help promote deeper roots, as well as allow the grass to out-compete weeds, such as crabgrass. Research has shown that tall fescue lawns mowed at 3 or 4 inches will naturally inhibit 85% to 100% of crabgrass germination.