All soils are composed primarily of mineral particles, ranging in size from fine, dense clay to medium-size silt to coarse, loose sand. The proportions of these ingredients—along with decayed vegetable and animal matter, known as humus—determine the texture and quality of the soil. Soil that has too much clay in it retains water almost indefinitely, causing problems with drainage. Sandy soil dries too quickly and allows nutrients to leach out.
The best garden soil is called loam and is a balance of clay, silt, and sand, with plenty of humus to help hold the mineral particles together and aid in the retention of moisture. Crumbly in texture, loam has plentiful spaces to let both air and excess water pass through, while nutrients are retained. Humus keeps the soil fertile and makes the soil easy to work.
Proper texture is only one requirement of good garden soil. In addition, the soil must contain nutrients necessary for plant growth, and it should be neither too acidic nor too alkaline—conditions that impair the ability of roots to extract the nutrients from the soil.
With a few simple tests, you can evaluate your soil’s texture and chemical composition. The water test shown at right can gauge the need for texture-improving organic amendments. Peat moss and dehydrated manure are two widely used amendments, but the best of all is compost; it adds nutrients as well as improving soil structure—and you can make it in your backyard (page 41).
For chemical tests, use an inexpensive soil-test kit, available at garden centers. Most of these kits contain an array of test vials and chemicals, along with charts for interpreting the results. There are tests for nitrogen, phosphorus, potassium, and—most important of all—the degree of acidity or alkalinity, known as pH.
The scale that measures pH runs from 0 to 14. Neutral soil has a pH of 7. Above 7, soil is increasingly alkaline; below 7, it is increasingly acid. Most plants grow best in slightly acid soil, with a pH level between 6 and 7; consult the appendix for plant preferences.
To reduce acidity, add dolomitic limestone, which includes magnesium, an essential nutrient. In light, sandy soil, 4 pounds per every 100 square feet will raise the pH by .5; add 20 percent to this formula for loamy soil and 30 percent in heavy, clayey soil.
Excess alkalinity is corrected by adding sulfur—either pure ground sulfur, iron sulfate, or aluminum sulfate. Pure sulfur acts more slowly than the others but lasts longer; iron sulfate puts iron in the soil, producing lush, dark foliage; aluminum sulfate must be used cautiously because too much aluminum can be harmful to plants.
To reduce the alkalinity in 100 square feet of sandy soil by a pH interval of .5 to 1, use 3 to 5 pounds of iron or aluminum sulfate, or ½ to ¾ pound of ground sulfur; use 1½ times as much in loamy soil, 4 times as much in clayey soil.
Add amendments to your soil 4 to 6 months before planting, to give them time to become thoroughly incorporated. Mix in organic amendments by tilling the soil (page 40). Broadcast dolomitic limestone or sulfur on the surface, then rake it into the top few inches.
For a small area, you can do the tilling with a spade and spading fork (page 40). To till a large area quickly and easily, rent a power tiller. A model that has the tines set behind the engine is more stable and generally preferable for a beginner; a model with tines mounted on the front is more maneuverable in tight places.
Do not till soggy soil; it will break up into large, heavy clods that can dry as hard as rocks. A good time for tilling is generally 3 days after a rain, when the soil is neither too wet nor so dry that the job creates annoying dust.
At several different spots within the area you intend to plant, dig holes about 6 inches wide and 6 to 9 inches deep. Slice a thin wedge of soil from the wall of each hole (right). Wearing gloves so that your hands do not affect soil chemistry, remove sod and any small stones or roots from the samples, then mix them all together in a plastic bucket with the spade or a trowel.
A water test for texture
Fill a quart bottle half full with water and add soil until the bottle is nearly full. Cap the bottle, shake it well, then wait for the soil particles to settle in layers—from 3 hours to a day. Measure the thickness of each layer—clay on top, silt in the middle, and sand on the bottom—and divide it by the total height of the soil column to get each component’s percentage. When you adjust your soil’s texture with organic amendments (page 41), add about 2 or 3 inches of peat moss, manure, or compost if the soil is less than 25 percent silt or more than 25 percent clay. For soil that is more than 30 percent sand, add twice as much.
Testing the pH level
Fill the pH test chamber of a soil test kit to the correct mark with soil and add the amount of chemical called for in the kit’s directions. Using an eyedropper, fill the chamber with water up to the indicated line (right). Cap the chamber and shake it to mix the soil and the liquid thoroughly. After the soil particles settle, compare the color of the remaining solution with the kit’s color chart. The closest match of colors indicates your soil’s pH level.
Turning the soil by hand
With the point of a spade, outline the area to be worked and divide it into sections 2 feet wide. Dig out the soil from an end section to the full depth of the spade (6 to 9 inches), depositing the soil on a plastic sheet or tarp (above, left). Then fill this trench with soil from the adjacent section (above, right). Spread the desired organic soil amendments (page 37) on the first section and work them in with a spading fork. Transfer the top 9 inches of soil from the third section to fill up the second, and add amendments. Continue in this way until you reach the last section. Fill the last trench with the original soil from the first section.
Operating a power tiller
Put the tiller in neutral, position it at one corner of the planting area, and set the tines to the correct depth—from 3 inches for heavy, clayey soil to 8 inches for sandy soil. Start the engine, shift into forward, and guide the machine along one side of the bed. Make a broad turn at the far end, and work back in the opposite direction, creating a U-shaped area of tilled soil. Continue back and forth until you reach the end, then reverse directions and repeat the pattern in the untilled strips (inset). If your soil is very heavy, set the tines at 6 inches and till again. Spread the desired amount of organic soil amendments (page 37) on top of the soil. Set the tines at maximum depth and till in a direction perpendicular to the first set of lines to work in the amendments. If the tiller bucks excessively, go more slowly and raise the tines slightly.
Making compost is somewhat like setting up a fertilizer factory in your own backyard. If organic matter is simply heaped in a pile, the composting process can take up to a year. But if you place the materials in bins that distribute heat and moisture evenly, you will have usable compost in just 3 or 4 weeks. The most efficient composting system uses three bins: one for fresh organic material, one for half-decomposed matter, and one for the finished product. You can buy bins—plastic barrels, for example—or you can make them.
One easy-to-build arrangement is shown below. These bins are 4 feet high and 3 feet square. No floor is necessary. The vertical posts, set into the ground for stability, are 2-by-4s. Grooves cut into the front posts with a router or circular saw allow 1-by-6 slats to slide in and out for easy turning of the compost.
Air circulation around the pile is very important. Here, the front slats are held apart by screws that are driven into one side of the boards. The sides and backs of the bins are heavy-gauge wire screening, held in place by 1-by-6 boards nailed to the top and bottom of the posts.
To start a compost pile, you need equal proportions of so-called “browns” (shredded sticks, sawdust, and leaves) and “greens” (grass and hedge clippings, garden refuse, and vegetable scraps). Other organic materials, such as wood ashes, fruit peels, crushed eggshells, and coffee grounds, are also helpful. Do not include diseased plants, invasive weeds, pet droppings, or cooked scraps, which will attract vermin.
Place 6 inches of coarse brown material on the bottom. Then add an inch of commercial manure to provide food for the microorganisms, followed by 6 inches of green material, another inch of manure, and an inch of soil. Water until damp, then keep stacking layers in the same sequence and proportions until the bin is full.
COOKING THE PILE
Leave the pile alone for a few days, then start turning it with a spading fork several times a week to speed decomposition. After a couple of weeks, shift part of the pile to the next bin, and add fresh kitchen and yard waste to the first; layering does not matter now.
Water both bins occasionally to keep the piles moist. In another 2 weeks, the compost in the second bin should be dark and crumbly; store it in the third bin until ready for use.