Vent: my neighbor swore by leaving the mower deck high in July, and my lawn paid for it
My next door neighbor Ray, who has kept the same push mower running for 19 years, stopped me at the mailbox in early July and gave me some free lawn advice. He said to keep the deck on the highest setting all summer because tall grass shades the roots and you won't have to water. Sounded smart so I did it for six weeks. By mid August my yard looked like a hayfield that lost a fight, and the crabgrass moved in thick along the driveway side. When I finally dropped the deck back down, the mower bogged out every ten feet and I had to go over the same strips twice just to make it look half decent. Ray's yard looks fine, but he also waters twice a week and I found out he fertilizes in spring, which he never mentioned. So now I'm doing a full scalp and overseed in September while he watches from his porch. Was his tip actually bad, or did I just skip the other half of what he does?
Scalping before overseed is the right call, just rent a power rake or dethatcher first or the seed won't hit dirt and you'll be feeding the birds instead. His tip wasn't wrong, it's just half a system. Tall grass in July does shade the soil, but only if you're also watering and feeding so the grass actually grows thick instead of going stemmy and letting crabgrass slide in. Drop your deck gradually over a couple mows instead of jumping from highest to lowest, or you shock the turf and the mower chokes on six weeks of wet clippings.