Although there are differences in optimal mowing heights among different types of grasses, for most home lawn situations, a mowing height of 3 inches is a good target. Some grasses can tolerate lower mowing heights, such as perennial ryegrass and Kentucky bluegrass, but mowing too low decrease root growth and makes the lawn more susceptible to drought and heat stress as well as increases the incidence of weeds and diseases. Never mow your lawn lower than 2 inches.
Some people recommend lowering the mowing height in the spring and again in the fall, but this is not absolutely necessary. It is more important to maintain the proper mowing height and to mow frequently. Continue mowing late into the fall until the grass has stopped growing, sometimes as late as late November. This will remove excess debris and decrease the chance of snow mold. Raising the mowing height in the summer is a good practice. This higher mowing height, encourages deeper root growth and increases the lawn’s resistance to drought stress. Even a 1/4 inch adjustment (one wheel notch on most rotary mowers) will make a big difference in the health of the grass.
Check your owner’s manual for the correct height setting or place the mower on a flat surface and use a short ruler to check the distance between the mower blade and the ground. BE SURE MOWER IS OFF AND DISCONNECT THE SPARK PLUG WHEN MAKING ANY ADJUSTMENTS AND WHEN CHECKING BLADE HEIGHT.