Once the grass of a new lawn reaches a height between 3 and 4 inches, it is ready for an initial trim. It is important to remove only about 1/2 to 3/4 inch the first time a lawn is mowed.
Not only is it important to make sure the mower's height is set appropriately, the throttle needs to be at the lowest possible setting. This gives the new lawn a less aggressive trimming for the first round. New seedlings cannot completely root themselves, so if the mower is going too fast, the young grass can be pulled out of the soil. This is why it is important to make sure not to water excessively during the initial stage of growing a lawn.
Subsequent trimming can be done at the mower's recommended settings for the specific grass type that comprises the lawn. Each subsequent mowing after the initial run should remove no more than 30 percent or about one-third of each blade of grass. This maintains a healthy root system for the grass, and it allows future sprigs and plugs to develop. This development helps spread the growth of a lawn into maturity and ensures soil cohesion, preventing erosion and runoff.