Mowing is a lawn care practice that helps to keep the lawn thick and healthy. But this doesn’t mean that you should start cutting the grass after noticing some new seedlings sprouting. If you mow too early, you are likely to rip the new growth out of the ground.  For first-time mowing, you should ensure that the grass has reached at least 3.5-4 inches long. This should take about two months, depending on the grass type.