Clay dirt is made up of tiny particles that cling tightly together. These particles cling to water, making the atmosphere wet and heavy. Grass roots need to be able to spread easily through the ground. Clay dirt makes this very difficult. If you amend the soil, though, you can successfully create a lawn with clay dirt. You must be willing to devote the time to site preparation to plant grass in this environment.
Remove debris such as stones and weeds from the planting area. Grass seed needs contact with the soil to germinate.
Fill in low lying areas with a quality topsoil. Dips will cause water pooling. Rake until the planting area is level.
Run a rototiller over the top of the clay dirt to loosen it up. Work to a depth of 4 to 6 inches. Make sure to dig until all the clay dirt is loose.
Test the soil pH with a test kit from a planting center or nursery. Add hydrated lime to boost the pH and neutralize it. Apply 12 ounces of lime per square yard of clay dirt.
Lay down 1 inch of sand and 1 inch of compost. The sand will help dry out the clay dirt and improve drainage. The compost adds nutrients. Work them into the top few inches of the dirt with the rototiller. Rake until smooth.
Enrich the dirt with a starter seed fertilizer. Follow the instructions on the label. The fertilizer will add the proper nutrients to the clay and create a green lawn faster. Use a broadcast spreader to apply it.
Spread the grass seed evenly with a mechanical or hand spreader. Too few seeds will result in gaps and too many will cause them to compete for nutrients.
Water the grass seed 10 minutes twice daily for the first two weeks. After that, cut down watering to once a day. Because of the amount of clay dirt present in the amended soil, pay close attention that you're not overwatering the seed.