Clay soil is dense and does not allow great water drainage. Poorly draining soil does not retain nutrients and causes either water run off or too much water retention, causing root rot or poor plant performance. Clay soil requires amending with the addition of organic matter. Organic material is essential to good plant growth because it adds nutrients to the soil and breaks up the soil so that it drains efficiently and retains a greater percentage of fertilizer.
Measure the length and the width of the garden. Multiply the length times the width to get the surface area.
Spread a 3- to 4-inch layer of organic material onto the area. Organic matter includes peat, manure, wood byproducts and homemade compost, says the University of Missouri. One cubic yard of material will cover 100 square feet.
Till the material into the first 6 inches of soil using a rototiller. Spread another 3 to 4 inches of sand onto the organic material and clay mixture and till this in as well.
Use a pH test every few weeks to determine whether the soil pH is balanced and is not changing too drastically due to the organic amendments. These tests are found at most gardening centers and contain instructions.