By Jan Phipps

To be a good gardener, it helps to understand a little about soil, especially if you consistently have problems growing plants in the ground.

About half of soil by volume is composed of partially decomposed rock material called mineral matter, mixed with the remains of plant and animal life called organic matter. Pore spaces between the mineral and organic particles comprise the remaining half. Those spaces are filled with air and water. For optimum growing conditions air and water occupy the pore spaces in equal proportions, or 25 percent each. Organic matter should be a minimum of 4–7 percent with the mineral matter making up the remaining bulk of 43-46 percent.

The mineral layer is further divided into three textures that are categorized by particle size: sand, silt, and clay.

Sand, the largest particle size, feels gritty and is visible by simple observation. Roots move through sand easily, it drains fast and also changes temperature rapidly. Since the particles are large, so are the pore spaces between them allowing nutrients, water, and air to flow through quickly.

Silt is a medium size particle and can only be seen with a microscope. It looks and feels like flour. Silt holds nutrients and moisture well, but water can run off before soaking in.

The smallest particles are clay which are so fine they cannot be seen even with a microscope. They hold nutrients and moisture well but tend to drain slowly. Clay takes longer to warm up and shrinks and cracks when it dries.

The ideal ratio is 30-50 percent of both sand and silt, 20-30 percent clay, with the remaining 10 percent organic matter. This ratio is called loam and combines all the best characteristics. It warms fast in spring, works easily, plus retains nutrients and moisture.

Now for the fun part: doing the "jar test" to determine the ratio of sand, silt, and clay in your soil. Take a straight-sided glass jar with a tight-fitting lid. Using a shovel, collect a scoop of dirt from the top 6" of soil. Break up the clumps and remove any extraneous matter like weeds or insects. Add 2 cups of the soil to the jar, fill the jar with water, tighten the lid, and shake vigorously until the soil particles are suspended in the water. Set the jar on a flat surface and start taking measurements.

At one minute, measure the sand layer on the bottom. At two hours, measure the silt layer that settled on top of the sand. At 24 hours, measure the clay on the top. To get the percentages, divide the depth of each layer by the total soil depth in the jar. Then multiply each by 100.

Do not confuse the soil jar test with a regular soil test. The jar test gives you percentages of the three textures and can be done at home. A regular soil test determines different nutrients present (or lacking) in your soil and must be sent off to a lab. Illinois Extension offers soil testing in the spring every year.

For soil or any other gardening questions, please contact the Illinois Extension Master Gardeners of Edgar County at 217-465-8585.