Get a Feel For It
The one most important physical property of your soil is its texture, which refers to the relative amounts of sand, silt, and clay in the soil as a whole. Texture gives a soil its feel and has much to do with how a soil can be used. A soil may be sandy, silty, clayey, or some combination of those. Collect a handful of moist soil from your garden spot and then rub some of it between your fingers. Sandy soil feels gritty. Silty soil feels smooth, like flour or talc.
Clayey soil feels sticky and will hold together in a ball. Most likely, your soil will be a mixture and will not fit neatly into one category. That’s good. The perfect garden soil has a texture known as “loam.” A loamy soil will have about 50 percent sand, about 25 percent silt, and about 25 percent clay. That mixture allows for optimum use of water and nutrients. A soil that is too sandy allows water to flow through too quickly and plants can dry out. A soil that is too clayey, however, gets waterlogged, and plants suffocate from too much water.
Sandy soils also tend to be quite poor nutrient wise, while clayey soils can be almost impossible to work. So, you want a mixture of sand, silt, and clay to get things just right. Here’s a quick test to determine the texture of your soil. Take a handful of the moist soil and roll it into a ball in your hand. If the soil will not form a ball or if the ball falls apart as soon as you open your hand, your soil is sandy. If the soil forms a sticky ball, it is clayey. If the soil forms a spongey ball that holds its shape when you open your hand without sticking to your fingers, you have a loam. Congratulate yourself if you have a loam soil–you are one step closer to the perfect garden. If your soil is sandy or clayey, you will have garden success–you just need to work with it a bit more. Read on.
Too Much Sand
With a sandy soil, you have two gardening options: plant sand-loving plants, or add soil amendments that will improve soil texture. A few common plants that prefer sandy soils are annual phlox, coreopsis, oregano, rosemary, Russian sage, tulips, and yucca. Most vegetables, however, do not fare well in sandy soils because water runs out too quickly, carrying with it valuable nutrients. To improve the texture of your sandy soil, apply a 1 inch layer of dry clay and then till it in a few inches. The clay can be obtained from a local nursery or landscaping company. You can also use “green manures,” which are crops grown for the purpose of tilling in later. Grow buckwheat, clover, or oats for about 6 months. Then till them into the soil before they mature. The added organic matter will boost your soil’s capacity to hold water and nutrients.
Too Much Clay
The best aid for a clayey soil is a good dose of compost or manure. Compost or manure can be added to the garden at a rate of about 2 pounds per square foot. Dig it in deeply, mixing the soil well as you dig. The churning of the soil and the addition of the compost or manure will lighten the soil, break up clumps of clay, and make it easier to work with. Another trick is to add gypsum, or calcium sulfate, to a clayey soil. Gypsum is often sold at garden supply centers as “soil conditioner.” Apply approximately 20 to 30 pounds of gypsum per 100 square feet of garden space. Also, be sure to stay off clay soils when they are wet. Do not till or walk on the soil after a rain. The compaction only makes the clay soil worse.
Get a Reaction
While texture is your soil’s most important physical property, pH is soil’s most important chemical property. Soil pH refers to the level of acidity or alkalinity in it. It is measured on a scale that runs from 0 to 14; 0 is pure acid, and 14 is pure alkaline. Most garden plants prefer a pH somewhere around 6- 6.5, slightly acid. Soils in warm and wet areas where rainfall is frequent are often on the acid side. Soils in dryer, cooler areas can be more alkaline. For example, a soil in eastern Virginia in the Southeast United States may have a pH of 4 or 5. A soil from the desert of Arizona may have a pH of 8 or even 9. Most garden soils will need a little amending to achieve optimum pH levels. The pH of the soil is important because it plays a role in the availability of nutrients. Some nutrients that are necessary for plant growth, such as iron, can only be taken up by a plant when pH is at a certain level. See Table 1 for the optimum pH suggested for a number of garden plants. To determine where your soil is on the pH scale, you can have a professional test conducted. Information on professional soil testing is available in the next chapter. You may also purchase a quick test from your local garden supply center and do it yourself. Do-it-yourself kits are fairly self explanatory. Professional tests will often come back with information on what to add to your soil to improve its pH level. In general, acid soils benefit from amendments of lime. Add about 2 1/2 to 10 pounds of dolomitic limestone per 100 square feet of garden space. A clay soil will need additions more toward the 10 pound side; looser soils will require less. Limestone can be bought at garden supply centers. You may also add ashes from your wood burning fireplace or stove. About 5 to 10 pounds of ashes per 100 square feet of garden works well. Lime takes a few months to work, but it will last for years. An alkaline soil benefits from additions of peat moss, sulfur, or aluminum sulfate. Add about 5 pounds of peat moss, 1 to 2 pounds of sulfur, or 10 pounds of aluminum sulfate per 100 square feet of garden area.