A large portion of the southern United States is in what is known as a transitional zone for lawns. In these zones, cool-season grasses, such as ryegrass, will not live through the hot summer months, but warm-season grasses, such as Bermuda grass, go dormant in winter. The solution for growing a green yard year-round is to seed coo-season grasses into the lawn with warm-season grass. Cool season grasses should be treated as annual grasses and reseeded every winter.
Mow your summer grass to its lowest recommended length, which is typically 1 to 1-½ inches.
Position a lawn dethatcher over the lawn at the point you want to start. A dethatcher shortens the layer of thatch on your lawn, which is a layer of grass roots, dead stems, stolons and rhizomes. A thick layer of thatch will prevent water from reaching the soil and stop seeds from germinating in the lawn.
Rake up the thatch debris from your lawn, bag them and have them taken away. Thatch may be used in your compost pile.
Place a soil aerator over your lawn in a starting position. Repeat this process up to four times, varying the pattern in which you push the aerator over your lawn each time. There should be between 40 and 60 holes per square foot in your lawn when you have finished. A soil aerator removes cores of soil from your lawn so that oxygen and nutrients can reach the soil through the grass thatch layer.
Spread compost in a 2-inch layer over your grass and comb it into the grass with a lawn rake. The compost will work its way through the root zone and soil cores to improve the soil beneath the lawn.
Fill a broadcast spreader with a cool-season grass seed such as ryegrass or Kentucky bluegrass. Repeat this process up to four times more, varying your path by 90 degrees.
Water your lawn up to four times daily using ¼ inch of water per 1 inch of lawn to keep the lawn damp enough to encourage germination.
Mow your lawn so that it remains 1-¼ inch long until the new grass reaches this length. After that, raise the lawn mower's decking to the grass's recommended length, which is typically between 2 and 3 inches long. Reduce the watering frequency and increase watering amounts until you water with 1 inch of water per 1 inch of lawn every seven to 10 days.