Gardening Articles: Flowers :: Annuals
Soil Common Sense
by Charlie Nardozzi
Soil Texture: What You Inherit
Soil is composed of air spaces and organic matter, but mostly mineral particles. There are three kinds of soil minerals: sand, silt and clay. The relative percentage of each of these particles in the soil makes its texture. Soil texture won't change unless you literally excavate your soil and replace it.
Sand has the largest soil particles (.4- to .01-inch diameter) and the largest pores between particles. A soil with 50% sand tends to drain well, dry out and warm up quickly, but also tends to be less fertile and doesn't hold moisture well throughout the season.
Silt soil particle size is between clay and sand (.01- to .0001-inch diameter). The characteristics of silty soil are similar to those of clay, but moderated by its larger particle size.
Clay soil has the smallest soil particles (less than .0001-inch diameter) and the least amount of water and air spaces between particles. Consequently, a soil with at least 50 percent clay will have all the opposite characteristics of sand. It drains, dries out and warms up slowly, but is very fertile and once wet, holds water well.
Soil Structure: What You Make
The way sand, silt and clay particles are grouped together in aggregates is called the soil structure. The size and arrangement of these aggregates influence the nutrient availability and drainage of the soil.
Whether you have dry, sandy soil, silty soil or wet, heavy clay soil, adding organic matter in its many forms will improve the soil structure. The ideal amount of organic matter in most soils is between 5 percentand 10 percent. Organic matter helps any soil become more like the ideal loamy soil. Here's how.
Microorganisms feed on organic matter and produce polysaccharides. Polysaccharides help form humus, which enables small clay or silt particles to stick together to form larger aggregates. Larger aggregates create more pores for water and air to flow. The soil drains better, the plants grow better because of the increased pore space and more nutrients are available.
In sandy soils, humus acts like a sponge to catch and hold moisture. Humus also helps accumulate nutrients, making a sandier soil more fertile.
Soil pH: Acid or Alkaline?
pH is a measure of the sweetness (alkalinity) and sourness (acidity) of the soil. It is measured on a scale of 1 to 14. A soil pH below 7.0 is considered acid; above 7.0 is alkaline. The correct pH for your plants is important because certain nutrients are only available to plants within a specific pH range. Usually areas of high rainfall have a low pH and areas of low rainfall have a high pH.
The ideal soil texture is loam. It is composed of 40% sand, 40% clay and 20% silt. The ribbon test will determine the percentage of clay in your soil and the jar test shows approximate proportions of sand, silt and clay.
Remedy for poor texture: In all cases, adding organic matter in the form of leaves, hay, grass clippings or compost will make a sandy soil hold more water and nutrients and a clay soil easier to work and more fertile, as well as drain better. Apply a four- to six-inch-deep layer of grass clippings, hay or leaves or a one- to two-inch-deep layer of compost and till it into the soil.