Fertilizing Sandy Soil
Most of the soils in and around Santa Maria are composed of fine sand (old sanddunes). In their native state they contain very few nutrients and are especially deficient in nitrogen. Most of these soils also have only poor to fair water holding capacity, so that the root zone (top) layers of soil tend to dry out fairly quickly.
On the other hand, these soils are excellent for buildings and homes. When these soils are watered down and compacted by heavy equipment, they tend to stay compacted and provide a good foundation for the concrete slabs on which houses and other buildings can be built.
In order to grow a nice garden under these conditions (low nutrient, compacted sand), several things are needed. Initially, the landscape and garden area should be worked up at least 12 inches deep (18 inches would be better) to get some air and pore space back into the soil. During this process organic matter should also be incorporated. Composted animal manures, composted potting mix, or other composted materials are ideal, but wood chips, lawn clippings, saw dust, leaves, silage, finely divided organic matter of any kind will help to loosen up and aerate the soil. After this is done, the landscape and garden can be planted. Special attention should be given to sites where trees will be planted, so that the roots of the growing tree can penetrate the soil and develop properly and “normally.”
Once the garden is established, I would suggest that the flower beds receive an annual top-dressing of composted manure. This practice adds more organic matter, and most composts contain about 1% nitrogen (N) plus about 1% phosphorus (P) and potassium (K). The top-dressing should occur in January or early February, so the spring rains can help move the nutrients into the root zone. Besides the top-dressing, the landscape and garden should receive small applications of garden fertilizer. I find that on sandy soils it is best to apply small amounts of fertilizer often rather than to apply larger amounts infrequently. Soluble fertilizers tend to leach through the root zone as the plant cannot use a large application all at once. Therefore, a light fertilization once a month during the growing season usually works well. If you are lazy like I am, applications every other month will also work. I top-dress my flower beds in February with about ½ inch of manure, then add fertilizer in late March, May and July. You can use either granules or liquid (hose-on applications) fertilizers. Usually a “general garden fertilizer” formulation with a “balanced” analysis works well.
Acid soil loving plants like gardenias, azaleas, citrus, persimmon and hydrangeas may need special attention. These plants often develop iron chlorosis.