Just what is clay soil and why does it matter? 

It's a combination of sand, silt, clay, minerals and organic matter that also contains some air and water. Clay soils are sometimes referred to as heavy soils and sandy soils are called light. To be classified as clay soil, it should be made up of about 50% clay particles, the finest particles found in soil. As far as the gardener is concerned, clay soil can cause a number of problems.

On the positive side, working with clay soils isn't necessarily all bad. It has good moisture and nutrition retention. But that same "good" moisture retention can also be a problem. Clay soil drains slowly. So, as snow melts and rains set in, clay soil tends to remain saturated long after average or sandy soils have drained. It is also much slower to warm up in spring. Clay compacts easily making it hard for roots to penetrate, resulting in stunted root systems. With clay soil, there are often problems with frost heave and root damage as the soil freezes and thaws during changing weather. More often than not, clay soil is alkaline (has a high pH) and that can be hard on plants too. And worst of all, the stuff is heavy, sticky and hard to work. Gardeners having to deal with clay soils can help enrich the soil through the practice of organic gardening.

Clay soil is sticky and feels like plastic. Silt is the middle ground, with much smaller particles than sand and it feels slippery when wet. A heavy clay soil will form a solid lump that is difficult to crumble when it's squeezed together. It's hard to get sandy soil to form a lump and it crumbles easily. Another easy way to check the soil is with a quart jar filled about half way with a sample of your soil and then topped off with water.

If you have it, add a teaspoon of Calgon. Put the lid on the jar and shake it energetically until everything is swirling around. Then set it aside and let it settle until the water clears. The sand particles are the heaviest and they will settle to the bottom within a few minutes. Within an hour or two, the silt will have formed the next layer. The fine clay particles will finally settle, but it may take a day or so. Organic matter may remain floating around on the top. Looking at the layers, you can now see, comparatively, just how much sand, silt and clay make up your soil. If the clay layer makes up half or more of your sample, you have a heavy clay soil. Soil that is equal parts of clay, silt and sand is called loam. Sandy soils have very little clay. The best way to do a percolation test is to dig a hole about 2 feet deep and a foot wide. Fill that hole with water and let it drain completely. Now fill it again and keep track of how long it takes to drain. If it drains in less than 12 hours, the soil should be able to support plants that require well-drained soil. If it takes 12-24 hours to drain, the soil is best suited to plants that tolerate heavy or clay soils. If it takes more than 24 hours for the hole to completely drain only trees that withstand occasional flooding will survive. continued....