Trying to grow a bountiful vegetable garden or lush lawn in hard clay soil can be both difficult and frustrating even for the most experienced landscaper or gardener. Malleable when it’s wet and rock-hard when it’s dry, clay soil needs supplemental organic materials for you get the most you can out of it. According to the Oregon State University Cooperative Extension, clay soil is capable of holding a lot of water but doesn’t allow the water or air to flow through the soil particles, which limits plant growth. Adding organic materials to hard clay soil maximizes the soil’s ability to hold oxygen and provides nutrients and growth for your plants.
Mark off the area of hard clay soil that you want to improve. It’s easier to work on a larger area of soil at one time rather than repeatedly improving small locations, so determine the maximum area of soil that you want to improve. For example, if it’s a garden, determine the largest dimensions that you may need for the next few years and mark the perimeter with string and a set of wooden stakes.
Remove all vegetation from the clay soil. If you’ve already grown a garden or flowerbed, simply remove the leftover plants. If it’s a new site, you must remove all of the sod. Use the shovel to remove the sod, which will be especially difficult because of the clay. Try to find some friends to help make the job go faster and easier on your back and your hands.
Collect and mix a range of organic materials. Common sources of appropriate organic materials include grass clippings, dead leaves, hay, straw, cow or horse manure, and fruit or vegetable residues. You should be able to collect most of these items for free from your own property or from neighbors and friends. Aim for your organic material mix to include about 50 percent brown, or carbon-rich, materials and 50 percent green, or nitrogen-rich materials.
Spread the organic materials across the surface. Use the garden rake to spread the materials over the exposed hard clay soil in a solid sheet. Your goal is to cover the soil with a 6- to 8-inch layer of well-mixed organic materials.
Mix the organic materials with your hard clay soil. You can use a variety of tools, including the shovel or a rototiller. A rototiller requires the least output of manual labor, but Oregon State University Cooperative Extension points out that rototillers can damage your soil structure. Unless you’re improving a very large area of clay soil with your organic materials, your most effective option is using a shovel or spade. This allows you to incorporate the organic materials as deeply as you wish.