Without a doubt, yes, they are. Mowing with a dull blade is like giving your lawn a bad haircut. Rather than cleanly cutting, a dull mower blade actually rips or tears grass blades. This not only increases the intensity of the plant injury, but also the ragged edges serve as ideal entry points for various lawn pests and diseases.
Dull mowing is especially visible in hot weather when the tip of each grass blade dries out and turns brown. Multiply this by several billion and your lawn may end up looking more like a field of straw rather than a lush green carpet.When mowing grass that is not wet at the proper height, a sharp blade ensures a clean cut that can seal quickly; which minimizes the potential for disease problems brought on by dull mowing.
On average, your lawn mower blade should be sharpened 2-3 times throughout the season, depending on the size of your lawn. The easiest way to manage this is to keep a spare blade handy that you can simply change when it’s time to sharpen.