Well-drained, nutrient-rich, sandy, loam soil is the ideal soil for gardening. However, few gardeners are blessed with perfect soil. Soil can be too sandy, composed of heavy, dense clays, or be too acidic. Soil often lacks the vital nutrients necessary for healthy plant growth. Don't despair. Garden soil can be greatly improved by adding organic materials and intense tillage.
Test the soil to determine nutrient content and pH levels. To prepare a soil sample, dig multiple test holes across the garden plot or landscape in a checkerboard pattern. Dig a hole 6 to 8 inches deep. Disregard the soil from the hole. Move back 1 inch from the diameter of the hole, take a clean 1-inch slice of soil 6 to 8 inches deep and place in a plastic bucket. Proceed to dig additional test holes in the same manner, placing each 1-inch slice of soil in the bucket. Mix all the soil samples together well in the bucket, breaking up clods and removing rocks and roots. Spread the mixture out on a layer of newspaper to dry. When dry, place 1 pt. of the soil in a ziplock plastic bag for submission to a testing facility. Soil tests are available from your local county extension office or the agricultural departments of most colleges and universities.
Plan to amend the soil as recommended by the results of the soil test. If the pH level is lower than ideal, add dolomite (calcium and magnesium). An application of 2.27kg. of dolomite to every 100 square feet of soil will raise the pH level by 1 point. The texture and permeability of heavy clay soil is greatly improved by adding gypsum to the soil. Gypsum is nontoxic to humans and animals, and does not burn plants. Following label directions, broadcast 13.6kg. of gypsum across every 1000 square feet of gardening space. Cultivate well into the soil with a garden tractor or tiller.
Add organic compost to the soil. Spread a thick layer (10 to 12 inches) of compost on the soil. Cultivate the compost into the soil. Repeated tillage is the secret to improving soil texture. Till the width and length of the garden plot several times until the compost is thoroughly mixed into the soil.
Add 22.7kg. of sand per 100 square feet of soil. If soil is lacking iron, broadcast blood meal per package directions. Cultivate well. Sand will improve the moisture-retaining ability of the soil and break up clay.
Apply a 4- to 6-inch layer of aged, non-treated sawdust or small wood chips to the gardening area. Cultivate into the soil, once again tilling repeatedly to integrate the sawdust into the soil. As you till the ground, remove tree roots and rocks. Do not till when the ground is wet. Tillage of wet soil will cause clumps and compaction. The goal is to till until the soil has a crumbly, mealy texture.
Cover the soil with a heavy layer (12 to 18 inches) of organic mulch. Straw, dead leaves, shredded newspaper, torn strips of cardboard, grass clippings or manure from herbivores (cow, sheep, horses, goats, lamas) may be used. Water well until the material and the soil are saturated.
Allow the soil to rest and the organic materials to decompose until the following spring. (If feasible, cover the garden plot with black landscape plastic. The plastic will trap the heat of the sun and conserve moisture, which accelerates the decomposition process.) In spring, remove the plastic and allow the ground to dry out. Repeatedly till the mulch layer into the soil. Rake and level. The soil is now ready for planting.
When preparing soil samples, make sure the sample is thoroughly dry. A damp sample can cause false results. Always gather your samples with clean tools and in a clean plastic bucket (do not use a metal pail). Residue from fertilisers, pesticides or herbicides will contaminate the sample.