How high you should allow the grass on lawns to reach before cutting it is perhaps the most frequently asked question about lawn care. And "How much of the grass blade should be removed when you're cutting grass?" is a natural companion to that question.An optimal height for a cool-season grass in fall is about 2 1/2 inches. And at each mowing, you should only be removing about the top 1/3 of the grass blade. Consequently, a good time to mow lawns is when your grass is about 3 2/3 inches high.
Why is 2 1/2 inches an optimal grass height? You’re striving for balance. Mowing the grass is like "pinching" a garden plant to stimulate rugged growth. If you let the grass get too tall, you’re not mowing very much, which means you’re passing opportunities to make your lawn healthier and more attractive. If you cut grass too short, you stress it.
The height of the grass should determine when it's time to mow. It would be arbitrary to establish a schedule for mowing based on length of time between mowing. For instance, advising someone to "mow every other week" fails to take into account the growing conditions during that period of time. For instance, rainfall stimulates growth in lawns, so the presence or absence of rain will have a great impact on mowing frequency.
While the 2 1/2-inch height for a cool-season grass is optimal for the fall, it is hardly an absolute figure that must be adhered to throughout the mowing season. If you have a crabgrass problem, for instance, you may wish to make an adjustment in spring and summer. That’s because it is during these seasons that crabgrass, an annual weed, competes for space with your lawn grass. Some experts recommend keeping lawn grass around 3 inches tall during spring and summer because the extra shading that results may inhibit crabgrass enough to keep it in check. In fall, you can go back to maintaining the 2 1/2-inch height, since, by then, frost will have killed the tender crabgrass.
