Cutting grass at the right height is important because mowing affects the depth of the root system.
Cool season grasses and fescue grow best when mowed at a height of 3 to 3.5 inches. During cool weather a shorter height is best. The height of the deck should be raised to 3.5 to 4 inches during the months of July, August, and September.
If the grass has been allowed to grow tall it is best to shorten it gradually. Grass should never be mowed to remove more than 1/3 of the grass height at any one time.
FACTS ABOUT GRASS CLIPPINGS
USING GRASS CLIPPINGS AS A SOURCE OF FERTILIZER FOR YOUR LAWN CAN SAVE TIME AND MONEY AND HELP PROTECT THE ENVIRONMENT. Leaving grass clippings on your lawn can generate up to 25% of the lawn's yearly fertilizer needs and reduce the amount of time and money you spend fertilizing and bagging. Lawns stay greener and healthier when clippings are left on them.
GRASS CLIPPINGS DON'T CAUSE THATCH. Thatch is caused by excessive growth from over-fertilizing, by allowing grass to get too high before mowing, or by incorrect watering.