Sowing new grass seed is the first step to a new or rejuvenated lawn, but you must still wait for the seed to germinate and grow before you may see the fruits of your labour.
Different types of grass seed germinate at different rates. Ryes and fescues may germinate within a week or two, while bluegrass and buffalo grass may take up to a month. Once the seed is germinated, the time it takes to grow long enough to cut may vary, but is usually about the same as the germination time.
To give your grass seed the best chance of producing grass, sow a variety that is right for your climate. Make sure the air temperature is above 18.3 degrees Celsius and rake the seed lightly after sowing, to mix it with the soil. Provide frequent light waterings just to keep the soil moist, and cover it with 1/8 inch of mulch if the soil is not holding the moisture.
Avoid using cheap grass seed, as it may be dormant or dead and likely contains weeds. Burying the seed too deep will prevent it from breaking the surface: The seed should be just lightly covered. Birds like to snack on grass seed, so keep them away with a scarecrow, a plastic owl or whatever works in your area. Never sow seeds in an area that has recently been chemically treated. The label on the treatment bottle will tell you how long to wait.