Planting winter grass seed is common in the warm southwest, but is also possible in snowy or cold climates as well. In the southwest, planting grass seed in the winter is called "overseeding" because you are planting over a dormant lawn of Bermuda grass. In snowy, cold climates, planting winter grass seed is called "dormant winter seeding" because you lay the grass seed either on top of or under the snow until spring, when it begins to grow.
Choose the method best for your lawn based on the climate where you live. In climates that have a very hot summer, such as southern Arizona, choose winter rye overseeding. In climates, where it is very cold or has snow, choose dormant seeding or placing the seeds on top of the cold earth or snow and wait until spring.
Whichever method you choose to plant grass seed, it is important to prepare the soil. Till the soil by turning it over with a rototiller or shovel and rake. Remove weeds, rocks, dead grass and sticks. Add good top soil if the soil is low in nutrients. Fertilize the soil with a starter fertilizer.
Choose plant seeds. For hot summer climates that have Bermuda grass lawns, choose winter rye grass. For dormant seeding lawns choose seeds that are still in their hulls, such as unhulled rye grass, unhulled fescue or unhulled Kentucky bluegrass. Unhulled seeds will be protected by their shell and lay dormant until the snow melts and the seeds sink into the warm soil.
Overseeding of Bermuda grass requires one of two methods of preparation and planting. Aerate your lawn by poking holes in the lawn with an aeration tool, or mow your lawn short and then thatch it with a thatching machine. Rent a thatching machine from a lawn and garden center or pay a landscaper to do it for you. Spread the winter rye on top of the lawn with a seed spreader and then throw down a layer of topsoil mixed with manure.
For cold, snowy climates, spread the unhulled seeds down before the first snow falls. The snow will hold the seeds in place.
Water the winter rye grass seed planted on top of the dormant Bermuda grass lawn. Keep the ground moist by sprinkling the lawn with water in the morning, and afternoon if the weather is very dry. Seed planted on top of snow will get watered by the snow melt, so you do not need to water the unhulled seed.