Topsoil contains a mixture of various ingredients, including sand, clay and decomposing vegetation. Although trees, flowers and vegetables grow in many types of soil compositions, certain soils contain excessive amounts of clay. Heavy clay soils hold water near the surface and limit the growth of roots. Healthy soils allow the passage of air and water to reach the roots. Increase the health of your garden and landscape plants by increasing the porosity and drainage in heavy clay soil.
Fill in any low areas to encourage drainage. Create a gradual and even slope away from structures and walkways. Fill in low areas with additional soil to create a level surface. Use a shovel to scrape soil from high areas to place in depressions. Clay soil drains slower than other soil compositions, so eliminate low areas to decrease unnecessary pooling in your landscape.
Till your soil in the fall to loosen it prior to spring planting. Use a garden tiller on dry soil before the ground freezes in late fall. Allow the natural effects of freezing and thawing to condition the soil over the following months. Choose to till on a day when the soil is dry to barely damp, to minimize damaging your clay soil.
Add organic materials, such as compost, straw and shredded bark. Spread the organic material over the topsoil. Work into the top 6 to 12 inches with a garden tiller. This provides adequate drainage near the roots of bedding plants and vegetables. Incorporate this organic material into the backfill of large holes when planting trees and deeply rooted shrubs.
Apply some ammonium sulfate with your organic materials to increase the amount of nitrogen in your clay soil. Organic compounds temporarily reduce the amount of natural nitrogen in the soil. Use about 1/4 pound of ammonium sulfate per bushel of organic mulch to guard against nitrogen depletion.
Construct a raised bed to provide adequate drainage in small areas of clay soil, such as herb gardens, flowerbeds and small vegetable plots. Use landscaping timbers or stones to build a 12-inch enclosure for your plants. Allow a little space for water drainage between timbers or stones. Fill the enclosure with a mixture of existing clay soil and well-draining potting soil.