Do you know the first rule of lawn mowing (other than bribing a teenager by withholding the car keys)?
The rule is: never cut more than one third of the standing growth. Proper mowing not only keeps the lawn attractive, it produces a lawn the resists weeds, insects, and disease, and prevents thatch. Proper mowing encourages the development of a healthy root system.
Here are some of the recommended lengths for various lawn grasses:
Bahiagrass: 2-3 inches
Bermuda grass: 3/4-1 1/2 inches (a little shorter for improved Bermuda grass)
Bluegrass: 2-3 inches (a 1/2 inch shorter for improved Bluegrass)
Centipedegrass: 1-2 inches
Fescues: 1 1/2-2 1/2 inches
St. Augustine grass: 2-3 inches
Zoysiagrass: 1-2 inches
So, if the recommended length is 3 inches, cut when the grass is about four inches long.
Keeping grass a little on the tall side--especially Kentucky bluegrass--prevents damage caused by scalping and helps to shade out weed seeds that try to get established.
If a lawn looks yellowish after it is mowed, you have waited too long and cut too deep. Your lawn may be shocked and at risk for damage by strong sunlight.
Lawns need to be cut frequently during the growth seasons and even more frequently if you have overdone the fertilizer. When the slow or dormant season comes, cut less frequently. In the North, set the mower 1-2 inches or more higher during the hot, dry months of summer.
Some northerners advocate setting the mower lower for the last mowing of fall. This prevents matting over the winter (discouraging disease and insect hide-outs) and opens up the lawn to the first warming rays of spring.
Photography by National Gardening Association.