Unlike sand or silt soil that crumbles in your hand when you close your fist, clay soil sticks together when you squeeze. Despite the fact that clay soil is nutrient-rich, plants that require an airier soil will struggle when planted in clay. Poor drainage poses the biggest threat to plants grown in clay soils. Amending clay soil will improve drainage and give the roots of your plants more room for expansion.
Break up the clay soil to a depth of 6 inches using a rototiller, after three to four days of dry weather. A pitchfork or garden spade will suffice for smaller areas. Remove large stones, branches and debris during the tilling process.
Fill a wheelbarrow with organic compost. Use your spade to shovel a 3-inch layer of compost onto the soil. Mix the compost into the soil at the 12-inch depth.
Add a 3-inch layer of coarse sand, also known as builder's sand, to the soil. Shovel the coarse sand onto the soil and work it in with your garden spade or pitchfork.
Test the soil to see if the drainage quality has improved after amending. Dig a hole 2 feet deep and 1 foot wide.
Fill the hole with water from a garden hose and wait for the hole to drain. If the water drains within 12 hours, the amended clay soil can sustain plants that require well-drained soil.
Any type of organic matter that is available to you will work for compost. Good choices include rotted manure, cut grass and leaf matter left over from the fall. A cubic yard of compost or coarse sand will cover 100 square feet of soil at a 3-inch depth. Add a 2- to 3-inch layer of compost to the soil around your plants each year. As the compost breaks down, it will further reduce the density of the clay soil.
If the drainage test fails, and the water does not drain within 12 hours, add an additional 1 to 2 inches of compost and coarse sand. Repeat the test afterward. Never amend clay soil when it is wet.