There is no easy way to prepare clay soil for growing plants, but if well prepared, organic matter added, well drained, fertilized, clay soils will support the growth of almost all plants.
Clay is composed of very minute particles which have a large surface to absorb water. High water content causes its stickiness. Clay soil should not be worked when wet because it puddles and hardens and makes a poor environment for roots. Digging too soon in the spring may make it practically useless for the season. Fine cinders, well-rotted manure and wood ashes are a benefit. Steam cinders are usually mixed with clay to make it better for flowers; a 2-inch layer spaded in will be safe. Steam cinders in clay soil are better than sand since they are of more help in opening it up and admitting air.
If you dig under leaves in an effort to add humus to the soil it is advisable to test the soil for acidity.
Chemical fertilizers The only chemical fertilizer which has a bad effect in clay is nitrate of soda. It causes the soil to become greasy and sticky. It is often necessary to furnish mineral elements so plants will grow. Ground limestone, a 2-inch layer, spaded into clay will make it more workable.
If your clay soil is slightly acid and in partial shade, add organic matter or peat moss to increase root growth. Slight acidity is all right for vegetables and for most ornamental plants. The physical conditions of an extremely wet clay soil can be improved by using 4-inch agricultural drain tile and the incorporation of liberal amounts of screened cinders or sand. Add ground limestone, as necessary, to lower the acidity.
The gray clay contains less iron than red clay and it is quite fertile, but it is better for plants if it is fertilized. Clay soils vary in their degree of acidity. To determine the reaction of the particular soil in mind, test it or send a sample to your state agricultural college.
When white clay becomes baked hard after a rain, it needs organic matter in the form of peat moss, compost, or leafmold to become loose and mellow.
Any plant will grow in sandy soil if fertilized frequently. Apply fertilizer high in phosphorus and potash. Extremely sandy soil needs loam but also plenty of organic matter. Add 3 inches loam and spade to a depth of 6 inches. However, without additional organic matter, on very sandy soil loam is usually lost by being washed down into the sand.
Some flowers grow better on sandy soils than others. These include Portulaca, California poppy, annual phlox, calliopsis, cockscomb, morning-glory, anthemis, milkweed, aster, baby's-breath, liatris, yucca.
The only way to make a vegetable garden on pure sand is in raised beds made out of 2- by 12-inch planks for sides. Lay plastic and set the beds, usually 3 feet by 12 feet, on this base. Fill with a good loam. If soil is heavy, punch holes in the plastic. Another way to solve this problem is to dig out the entire garden to a depth of 12 inches, lay down plastic, and replace the soil. Either method slows up loss of fertility and water.
To grow roses on sandy soil, add manure, compost, or peat moss. Keep soil fertilized and water heavily when necessary. Plenty of organic matter will be needed or roses will do poorly.
If the soil is solid sand, surfacing it with a layer of topsoil will not be sufficient for planting fruit trees. A very large hole should be dug for each tree and filled with good soil in which to plant. If you are on the seashore where there is a lot of sand and the soil is acid, establishing a vegetable garden will require additional efforts: increase the organic content of the soil by incorporating green-manure crops, farm manures, or other nonacid materials such as leaves, straw, plant refuse, or nonacid peat. Apply lime as needed to modify the acidity.