Mowing a new lawn requires special care. New grass blades are delicate and sensitive, and can be harmed much more easily than more seasoned growth. Be as gentle as you can to your new lawn, and you will reap the benefits of a thick, green, well-established lawn.
Wait to mow. Your lawn should be 3 to 4 inches tall and well-established before you mow it. Pick a day when there is no rain, and do not water your soil for 24 hours before you mow it for the first time. This will prevent the blades from sticking together and minimize the damage you and your mower will do to the soil by treading over it.
Thickening Your Lawn
If your new lawn is patchy, use mowing and aerating to help thicken it up. Mow the lawn down to about 1 inch tall over several days (you should never mow more than a third of your grass in a single mowing). Then, run a core aerator over your lawn to break up the soil. Finally, reseed your lawn with a seeder. The new seeds will help your new lawn grow in thicker and fuller and the mowing will shock the lawn, stunting the old grass and allowing the new grasses to grow in.
Take care to protect the roots the first time you mow. Move the mower slowly and corner carefully to avoid tearing up the grass. Your new grass seedlings will have shallow roots, which can be very easily damaged by aggressive mowing. To go even easier on your grass, start off by using a reel mower. While rotary mowers rip the grass blade with a spinning blade, rotary mowers snip the grass blades like scissors, placing less stress on them.