Does mowing harm grass plants? Not if the cutting blade is sharp. It’s like pruning shrubs or deadheading old flowers. Mowing removes the old growth and stimulates a lawn to spread out, thicken up and choke out weeds. It’s not only important to mow – it’s important to mow properly. Mow on the high side to encourage a deep root system. Be sure to mow in a different direction each time, so turf doesn’t develop a "lean", leaving spikes of uncut grass. And mow often enough to cut the top one-third of the grass plants. This will help promote a healthy root system.