I have mentioned in previous columns a very common phrase in gardening don’t guess; soil test. When gardeners speak – or in my case – write the phrase, it is in reference to a laboratory analysis. The lab results measure the nutrients in the soil, their availability to the plant, the soil pH (measure of acidity), and organic matter. What this test does not reveal is the soil’s texture.
What is soil texture? It is the amount of sand, silt, clay, and organic matter in the soil and how it is distributed. Soils in our area are generally well-weathered fragments from granite rock, known as parent material. If we measure these fragments, we start with 2 millimeters (mm). Particles larger than 2mm are referred to as course. Sand ranges from 2mm down to 0.5mm and feels gritty. Silt is 0.5mm down to 0.002mm and feels floury (yes, floury is a word). Clay which is less than 0.002mm. If you are thinking to yourself that clay can be a thousandth the size of a grain of sand, you are correct.
Soil texture effects how water and nutrients are retained. Sandy soil does not hold nutrients or moisture nearly as well as clay soil. The loss – or leaching, as it is referred to – means they are not available to plants. Clay soil on the other hand is so small that water has difficulty draining, roots have difficulty penetrating, and when it dries it is, well, a brick. As gardeners we want what is referred to as sandy loam, a mixture of 50 percent sand, 40 percent silt, and 10 percent clay. Sandy loam is like gold to gardeners, but rarely do we have it. Frankly, your soil texture is only going to change if you remove it and replace it.
Instead of removal, improve the situation by adding organic matter such as yard waste compost. Compost added to clay soil improves drainage, adds porosity, and reduces density. Compost added to sandy soil also improves drainage as well as the soil’s ability to hold nutrients longer because of the reduced leaching. Regardless of clay or sand, improving soil is a continuous effort, not a one -and-done.
Okay, how do we determine our soil texture? One way is to take a sample to a soils laboratory for a texture analysis. Another one that is less accurate is to conduct the jar test at home. The test takes a quart jar with a leak-proof lid, a trowel, water, soil, a ruler, and a calculator.
Start by taking five to seven samples of your soil down to about four inches for lawns and most perennials or six inches for trees. Lay the soil out on newspaper to dry for a day. After drying, remove any rocks, roots, and grass. Then, finely pulverize the soil and add it to the jar until the jar is one-quarter full. Next, add water until the jar is three-quarters full and add the lid. Now shake the jar for 10 minutes. The shaking separates the particles. Place the jar in a place where it will not be disturbed for two days. The sand will be at the bottom, the silt in the middle, and the clay at the top. A fine line of organics will float, so it cannot be measured. Place the ruler beside the jar and measure the sand, silt, and clay thicknesses – recording each – and add them for a total thickness. Next, calculate the percentage of each by dividing each type by the total thickness. For example, your clay thickness is 0.5 inches and your total is 2.5 inches. Divide 0.5 by 2.5, and you get 0.20, or 20 percent. Yes, gardening does involve math. If you have access to the Internet, search the USDA Soil Textural Triangle. Plot each soil percentage and determine your soil’s texture. No internet? Call the extension office at 751-4401. Tell the Master Gardener on duty the percentages and they can inform you of your soil texture.
There it is my fellow garden enthusiasts; you know have the dirt on soil.
