Clay soil is characterized by slow drainage, sticky texture and a plastic-looking appearance. It is often difficult for plants to survive since most need adequate water drainage. Unfortunately, simply mixing sand with the clay will not successfully improve it. Rather, a combination of sand and organic matter, applied at a rate that creates a 50-50 mix of the original clay and the sand and organic matter, is needed. The amending process creates a slightly raised bed, which also helps water drainage, that is ready for most plants.
Measure the area in which you are going to amend. For example, a 10-by-10-foot space equals 100 square feet. The square footage of the space determines how much sand and organic matter is needed. The larger the area amended, the better off plants are, since their roots aren't confined to the small improved area.
Purchase builder's sand or sand labeled as coarse. To add 3 inches of sand, you will need about one cubic yard for every 100 square feet; therefore, it may be more advantageous to buy it loose rather than in prepackage bags. Loose sand is often available at garden centers and local landscaping companies.
Obtain coarse organic matter, such as compost, wood chips or aged manure. Local yard waste facilities, garden centers and landscape companies may have what you need. Like the sand, about one cubic yard is needed for every 100 square feet in order to add 3 inches to the soil.
Spread evenly the organic matter over the area to be amended and mix it into the top 6 inches of soil. A rototiller makes quick work of this step, particularly for large areas. If a rototiller is not available or cannot be rented, a shovel, hoe and garden rake can be used. However, this is much more labor intensive.
Spread the sand over the area and mix it into the clay soil and organic matter mix. The new soil now consists of 6 inches of original soil, 3 inches of sand and 3 inches of organic matter.
Amend the soil further when planting, if necessary. If some of your plants require deeper planting than the depth of your amended soil, dig holes that are twice as wide and just as deep as the plants' current containers or root balls. Then, for every extra inch in depth, mix in 1 inch of sand and 1 inch of organic matter into the soil you dug out before planting your plants. Alternatively for container plants, dispose of the extra clay at the bottom of the hole because you can plant using the containers' soil.