How Long Does Grass Need to Grow Before You Mow?
When starting a new lawn, early maintenance is critical for its long-term health, and mowing is no exception. Grass should be allowed to grow to one-and-a-half times its recommended height before its first mowing, or about 4 to 5 inches if the recommended height for grass is about 3 inches.
When to Mow
Grass started from seed takes about two months to reach a height suitable for mowing, while grass started from plugs or stolons and sprigs needs about three to six weeks before mowing. Sod should be in place for at least two weeks before running the mower over it. Mow new grass when it is dry. The roots are still pretty weak and mowing wet grass not only clogs the mower, but it also tears new grass from the soil with even the slightest pull. In dry ground, the soil is firmer and the roots more secure.
How to Mow
Only take off about one-third of the grass’s total height, even if this doesn’t bring it down to the recommended height for the particular type of grass. That will leave plenty of leaf blade for photosynthesis. Take gentle turns, as sharp turns will also tear out the grass, even if the soil is dry.
Type of Mower
On a new lawn, it's best to use a hand-powered reel mower over a gas-powered rotary mower. Reel mowers make a clean cut across the grass blades, while the often dull blades of a power rotary mower have a tendency to tear the grass. The reel mower allows you to tidy up the lawn’s appearance without damaging the blades. Once the grass is truly established, it’s OK to use a gas-powered mower.
Once you’ve made the first pass, let the grass sit for a few days then mow it again, this time to the recommended height. Always remove no more than one-third of the grass and leave the clippings on the lawn to act as a mulch/compost. Sticking to the one-third rule slows the development of thatch in the lawn, which is an accumulation of dead plant material that can suffocate the grass.