Test the Texture
To test your soil’s texture, rub a pinch of moist soil between your thumb and forefinger. Soil that is too sandy feels gritty and will crumble. Silty soil feels smooth and slick, while clay soil feels sticky and rolls up easily. Good garden loam feels mealy, and it may contain about 50 percent sand, 25 to 30 percent silt, up to 25 percent clay, and five to 10 percent organic matter.
Estimate Organic Matter
To estimate how much organic matter is in your soil, drop a spadeful of moist soil on a hard surface; if it breaks into crumbs half an inch (13 mm) in diameter, its organic matter content is close to ideal. If it breaks into large clods or shatters into a sandy pile, it needs substantial amending.
Rich soil teems with more than a dozen of the nutrients plants need for growth, including trace elements. Soils that are naturally rich are usually limited to bottomland near rivers, which is enriched with organic matter each time floodwaters recede. Lean or infertile soils contain few plant nutrients. A soil test will tell you how your soil rates in terms of fertility, as will plant growth; plants that grow slowly and never reach the size they should are a clear indication of low soil fertility.
The single most important way to improve all soils is by adding organic matter. Work one to four inches (three to 10 cm) of rotted manure, compost, chopped leaves, or other organic matter into the soil each year to turn any type of soil into fertile garden loam. Dig as deeply as possible, because digging or deep tilling aerates the soil. Beneficial soil microorganisms need oxygen to break down organic matter and release nutrients.
Avoid Compacting Your Soil
To avoid compacting the soil by squeezing out the air pockets and pushing particles together, don’t walk on, work in, or drive machinery over it when it’s wet. Neither air nor water can move through tight, compacted soil.
Soil Problems to Watch for
Several common soilborne plant diseases and pests are permanent residents in gardens. If you’re new to an area, talk with gardening neighbours or master gardeners to find out if fusarium, verticillium, or nematodes are prevalent in your area. If they are, choose plant varieties that offer genetic resistance to these diseases, because it’s impossible to rid the soil of them entirely.
Some leafspot diseases overwinter in soil, so they can be spread to leaves when soil is splashed on foliage during heavy rains or routine watering. Use a soaker hose or drip irrigation and water only in the morning, so leaves can dry off quickly. Also use mulch, which forms a barrier between the soil and plant leaves.
Heating soil with solarization can rid it of weeds, insect and disease problems as well as soil-dwelling nematodes.