Renovate an old or sparse lawn by overseeding. This means dropping new grass seed into an already-growing lawn, after having properly prepared the area by removing weeds and thatch, adding fertilizer and then roughing the soil surface. Watering frequently over a period of weeks will bring you good grass growth from the new seed at much lower cost than restarting a lawn entirely. Lawn renovation by overseeding should be done in the fall or spring when young grass plants have time to establish root systems in cool, moist conditions before summer heat arrives.
Clear existing weeds by spot spraying with weed killer before starting your overseeding project. Wait until the weeds turn yellow or brown--about a week--before continuing to the next steps.
Cut existing grass short, about two inches or less high, and collect the clippings. This helps expose thatch that must be removed, and also shows bare soil patches where seeds are most needed.
Remove thatch by raking with a firm-tined rake, pulling up the dead plant material covering soil and surrounding existing grass plants. If thatch is deep, rent a de-thatching machine for the work, or hire a landscaper to do it.
Scarify or roughen the soil to open holes and crevices where grass seed can make contact with the soil. Do this with a firm-tined rake, or rent plugging or verti-cutting equipment, especially for large lawn renovation projects.
Choose the correct grass seed for your climate and the lawn renovation area. Many grass seed mixtures are available for use in sunny and shady areas, but be sure to buy seed from a reputable dealer to avoid getting poor quality seed or mixtures that contain weed seeds.
Work into the soil a light, seed-starting fertilizer in granular form. Spread it by hand or with a lawn spreader, and then rake it evenly into the loosened soil.
Spread grass seed using a lawn spreader or a hand spreader, applying half the recommended seed concentration in one direction, following with the remaining seeds,and then going in a different direction. Cover grass seed on bare soil with a light patch of straw to protect it until it sprouts.
Water immediately after spreading seed, using a light spray until the soil is thoroughly moist and the seeds are tamped down and in contact with the soil. Water at least twice a day until seeds sprout; then water enough to keep the soil moist over the next two weeks.
Cut new grass after it reaches two to three inches high and is fairly dense in growth. This may take about a month, so don't be in a hurry to mow newly sprouted grass.