Clay soil can cause several problems even though it retains moisture and nutrition well. Heavy clay soil drains slowly and, because it is so compacted, it is hard for plants to establish a strong root system. It is very heavy, sticky and hard to work with, with a tendency to freeze and thaw during the winter, contributing to root damage. Other soils can be added to clay soil making it more manageable to plant vegetation and grass.
Spray your lawn area with a non-selective herbicide that kills unwanted grasses and weeds. Choose a herbicide with glyphosate as the active ingredient; it does not harm the soil or move through the soil to other plants. Glyphosate kills weeds and weed-like grasses such as crabgrass, yellow foxtail, yellow nutsedge, wild onion and star-of-Bethlehem.
Till the clay soil 4 to 6 inches deep and mix 1 to 2 inches of sandy loam soil into the clay soil using a rake or tiller. Sandy loam soil consists of 30 percent or more of coarse sand, 30 percent fine sand and the rest silt. This mix helps break up the stickiness of the clay.
Rake the soil to your desired grade, removing any rocks, roots and debris. Grading your soil sets the slope of your lawn and the drainage. Ideally, your lawn should slope away from your house, descending 1 foot for every 50 feet.
Plant grass seed using a hand spreader to eliminate the wheel ruts from a push spreader. Make two passes with your seed, one pass north to south and the other east to west. Making two passes will eliminate any bald spots on your lawn.
Water your new lawn lightly and often until the root system is established.