In warm climates summer grass often goes dormant during the cooler months of November through April, leaving the lawn looking brown and unsightly. Even if the temperatures stay warmer, the waning sun and shorter days tells the grass it's time to rest. Planting winter grass by overseeding the lawn keeps the yard green and attractive through the winter until the summer grass comes out of dormancy in May.
Watch the temperature. Summer lawns start to slow down their growth when temperatures cool off. Winter grass seed prefers to germinate in cooler temperatures. When the highs are below 75 to 80 degrees it's time to start the winter lawn. Overseed too early and the ryegrass seeds will burn out.
Mow the summer grass as low as possible. The lower the grass the higher the probability that the winter grass seed will reach the soil and not be held up by sprigs of grass. Mowing as low as possible also slows down the growth of the summer grass so it doesn't compete with the new winter grass.
Rake the area to be overseeded. Remove as much of the mown grass as possible. Summer lawns of Bermuda grass usually grow by runners; if enough of the runners are raked up you may have to mow again to get rid of them. Go over bare patches in the lawn to loosen up the soil. This can be done with the rake as well or with a hand shovel.
Water the area well.
Broadcast the winter grass using a seed broadcaster or by hand if the area is small. As you're walking backwards take a handful of seed and throw it out in an arc in front of you. Spread the grass seed evenly. After a few tries you'll get the technique down.
Cover with topsoil. The cover doesn't have to be deep. The grass seed will sprout even if uncovered but the topsoil hides the seeds from the birds and retains moisture.
Water after planting and then at least twice a day for five to ten minutes until the seeds have germinated. After the grass is up taper off the watering to two or three times a week. Mow the grass when it reaches 3 to 4 inches high using freshly sharpened blades. Fertilize after the second mowing and then about once a month.