You should mow this type of lawn two an one-half to three inches above the soil line. Grass cut to this height shades the soil, and helps keep weeds from establishing themselves. This shade also keeps the soil temperature cooler. The higher you mow your lawn, the less frequently you need to do it. Mowing the grass shorter may make it more susceptible to injury from drought and disease.
Shorter grass has a smaller, shallower root system.
Thus, during dry spells, with a restricted root system, the grass may not have access to enough soil water to sustain growth and function. Remove no more than 40 percent of the total plant height in one mowing. For example, mow the lawn back to two and one-half inches when it is four inches high. You can grow grass longer in stress areas, such as shade and dry, sunny slopes. It is important to have a sharp mower.