Soil Savvy

by Elmer Krehbiel, Master Gardener
July 18, 2003

The soil determines the health, growth, and production of our plants. The ideal soil is a complex mixture of mineral elements (45%), organic matter (5%), air (25%) and water (25%) for most garden and landscape plants in this area. Then there are the acid, neutral and alkaline soils, and the clay, loam, and sandy types to consider.

Physical Property

Physical properties of the soil are visible, but may not be easy to improve. The most desirable soil is crumbly (friable), so the plants roots, water, air and fertilizer elements can penetrate easier. Soil type determines texture and how easy it is to till.

Clay soil may be mellowed with gypsum and organic matter. Sandy soils may be mellowed with organic matter.

Gardeners can prevent compaction by not walking on the soil (plant in two-, three- or four-foot wide raised beds), minimizing cultivation, nit tilling when soil is wet, and leting the soil lie fallow once every several years.

Chemical Property

Chemical properties are not visible, but they must be suitable for the plants health, growth, and production.

The pH is a logarithm scale that measures the acidity (0 to 6.9), neutral (7), or alkalinity (7.1 to 14) of the soil and water. The pH is a major controlling factor for roots to absorb nutrients. Each plant species has an adaptable pH range. The pH range preference list includes hundreds of flowers, grasses, herbs, houseplants, shrubs, trees and vegetables. The preferred range of the soil/water is 6.0 to 6.8 pH for most garden plants, 5.5 to 7.0 pH for most landscape plants, and 4.0 to 5.5 pH for acid-loving plants. The pH range for crape myrtle is 6.5 to 7.5, and for tomato it is 5.5 to 7.5.

Chemically, sulfur amendments will lower the pH and limestone applied will raise the pH. Organically, compost, peat moss, and shredded bark applied will lower the pH. Local water and clay soil types are alkaline. Amendments must be well mixed into the soil, but still may require a year or so to become completely effective.

The major elements (macronutrients) nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur are in the soil. The minor elements (micronutrients) iron, zinc, molybdenum, manganese, boron, copper and chlorine are also in the soil. Carbon, hydrogen, and oxygen are in the air and water. The roots absorb the nutrients (98%) from the soil, after they are dissolved in the soil moisture. Foliar feeding is usually not an efficient method to fertilize plants.

Earthworms in the soil indicate excellent conditions.

Do not disturb the soil if it is so wet that it sticks to you and your garden tools!

If the soil in your garden did not develop a bumper crop of flowers and/or vegetables, now is the time to have soil samples analyzed. Samples should be taken when no crop is growing in the soil. They should represent the problem area, and be taken from the surface to the depth of the root zone of the next crops.

It may be advisable to analyze subsoil samples to stop some problems. After obtaining a topsoil sample, place the probe into the same hole and push it down to 16 to 24 inches deep for the sub-soil sample.

You can obtain detailed information about soil testing from the Brazos County Extension Office, 2619 Highway 21 West, or call 823-0129.

More on Soil for the Garden

Dr. Elmer Krehbiel is the former President of Keep Brazos Beautiful. See his column in The Eagle.