Grass seed tends to grow in many different types of soil. A clay-based yard, however, can be challenging. Clay is a very heavy, wet substance. It does not contain many air pockets, which makes it difficult for grass seed's roots to spread and develop. Clay is made of tiny particles that cling to wetness. To successfully plant grass seed, you need to loosen up the soil and get rid of some of the moisture. More fertile, drier soil will lead to successful grass germination.
Remove debris such as rocks and sticks from the planting area. Use a shovel to dig up large rocks. Grass seed needs to touch soil to germinate. It will not grow well if on top of debris.
Cut up weeds, old grass and roots with a sod cutter. You can rent gas-powered sod cutters from a landscape company or rental company.
Till the top of the clay soil to loosen it up. Run a rototiller at least 4 inches into the ground. This adds air pockets to help the grass roots develop and spread.
Level the planting area. Pour topsoil into the dips to even them out. Dips will cause water to pool, which could wash away the grass seed. Rake until the area is smooth.
Add compost and other organic materials to the clay to make it more fertile. According to Gardening Know How, you can use well-rotted manure, compost or leaf mold. Spread 3 to 4 inches of the organic material on the clay and till it into the top 4 to 6 inches of earth.
Get a pH test kit from a garden center. Test the pH of the clay soil. Grass prefers a pH between 6.0 and 7.5. If yours falls into that range, you do not need to make amendments.
Adjust the pH of the soil if necessary. Add hydrated lime to boost the pH of acidic soil. You should add 12 oz. of lime per square yard of earth. This will increase the pH by 1.0 point. Add 3.6 oz. of ground rock sulfur to 1 square yard of clay to lower the pH of alkaline soil by 1.0 point.
Fill a broadcast spreader with a starter fertilizer that is high in phosphorus. The package should tell you how to set the machine. The food will add nutrients to the clay to make the grass seed sprout faster. It will lead to a thicker lawn.
Rake the fertilizer and soil amendments into the clay well to make an even mixture.
Disperse grass seed with a push spreader for large lawns and a hand spreader for small spots. Check the seed bag to determine how much seed to use for a particular area.
Cover the seed with 1/8 to 1/4 inch of soil. Run the backs of the tines on a leaf rake over the seed gently to achieve this. The layer of soil will keep the seed in place and help it germinate faster.
Water the seed twice a day for five to 10 minutes. Cut back on watering after two weeks. Water it once a day. If you let the clay soil dry out, you can lose up to one-third of the grass seed.