Human error, improper blade maintenance and incorrect mower adjustment are all reasons that a mower may not only fail to cut smoothly but also leave behind rows of uncut grass. These rows make the lawn look untidy. They also may interfere with the "striping" that lawn mowing leaves behind as it becomes necessary to backtrack over even passes in order to fix a missed spot. It also adds extra time to the job.
Poor equipment operation can cause missed swatches of tall grass. Running the mower at too low an engine speed rather than opening up the throttle not only stresses the engine but causes it to miss spots and strips because the blades are not spinning quickly enough. Taking turns too quickly and too sharply, especially with models that don't have a floating deck causes missed grass. Incorrect tire pressure or tires that are unevenly inflated causes missed strips as well. Misjudging the overlap of your passes also accounts for missed rows.
Mower blades cut with the tip of the blade. As the blades dull, they begin to tear at the grass rather than cutting it evenly and cleanly. Keep blades at their optimum sharpness all the way to the tip. When replacing the blades after sharpening, it is an all-too-common mistake to put them back on the mower upside down, which also causes improper cutting. The inside deck of the mower must be kept clean and free of impacted clippings; otherwise, air flow is disrupted or cut off. Air flow lifts the grass toward the blades for smooth and even cutting.
You can correct the problem by checking the air pressure in the tires and the deck height, as well as double-checking that the mower blades are installed correctly. If you are unsure of the adjustments that need to be made, have your mower serviced by an authorized repair technician. If you are familiar with machines and lawn care equipment, a quick read-through of the manual may allow you to diagnose and correct the problem yourself.
If you have recently replaced the blades on your mower and notice rows of missed grass, double-check the blade size. Blades that are too short or small for your model mower will fail to fully cover the cutting area, leaving unsightly strips of uncut grass behind. If this is the case, the only remedy is to replace the existing blades with blades that are the correct size for your mower model.