Most of the Southeast falls in a transition zone for lawns, meaning that warm season grasses such as St. Augustine, zoysia or Bermuda go dormant and turn yellow in winter. For lawns to stay green year-round in these zones, homeowners should overseed warm season grasses with a cool season grass such as rye or Kentucky bluegrass.
Mow your warm season grass to its lowest recommended level, typically 1 to 1½ inches high.
Check the thatch level in your lawn. Thatch is a combination of grass roots and runners, dead grass stems and debris. Thatch more than an inch thick prevents water, nutrients and grass seed from reaching the soil. To reduce the thatch level in your lawn, rent a dethatcher from your nearest garden center. A dethatcher contains vertical blades that cut through the thatch and operates similarly to a lawn mower.
Position your dethatching machine at the starting point on your lawn. Start the machine with the pull rope and push it over the lawn in sections. Make a second pass over your lawn, walking in a pattern perpendicular to the first.
Rake up the grass debris left by the dethathcher. Bag the debris in lawn bags and discard.
Position a soil aerator over the lawn and start it with a pull rope. A soil aerator, available from a lawn and garden center, operates like a lawnmower and removes soil, thatch and grass in round, narrow cores. Push the soil aerator over the lawn in sections the way you push a lawnmower. Pass the aerator over the lawn up to four times, varying the pattern each time. When you have finished, there should be 40 to 60 cores removed from your lawn.
Spread compost over the lawn as a top dressing. Rake it into the grass and aeration cores using a leaf rake.
Water the lawn using 1 inch of water per 1 inch of soil 24 hours before seeding.
Pour cool season grass seed into a broadcast spreader set to distribute seed at a medium rate. Slowly push the spreader over the lawn in sections. Make a second pass with the spreader, varying the pattern by 90 degrees.
Water the lawn using ¼ inch of water per square inch of lawn up to four times daily until the grass seed sprouts. Gradually reduce the watering rate to 1 inch of water per 1 inch of lawn once weekly.
Mow your lawn 1 to 1½ inches tall until the new grass reaches this height. Then raise the deck of your mower to the cool season grass's recommended height.