Wait as long as possible before mowing your newly sodded lawn for the first time. Generally, about 6-8 weeks after sodding is sufficient or allow the grass to grow up to 1/3 higher then its normal height before cutting. It is a good idea to let the grass grow at least 3 inches tall; 4 is better. For that first mowing, take just a little off the top and come back 2 or 3 days later and take it down to two inches.