Fall is a great time to test the soil and alleviate questions about fertility in your vegetable gardens or beneath that beloved shade tree. Fall soil testing allows the gardener to make additions to the soil before winter.

Individual types of plants (vegetables, trees and flowers) require ideal soil pH and nutrient levels to thrive. The soil test is a scientific way of gathering pH and nutrient available information and using it to make decisions on what plants to grow and/or what can be added to the soil to optimize productivity of crops. A soil test also enables the gardener to apply only what the plant needs and minimizes fertilizer runoff and its negative impact on the environment.

It is a rule of thumb to test soil often to see if pH has been altered or nutrients have been depleted. For instance, potassium is incorporated back into the soil but phosphorous is taken into the plant and may need to be amended. Potassium is usually only needed in low levels in our mid-Illinois soils.

A standard soil test reads the soil pH, phosphorous, potassium and organic matter. pH is important information for a gardener to know because some vital nutrients are unavailable if the pH is too high or too low. The ideal pH for garden and turf soils is 5.8 to 7.0.

Phosphorous is responsible for root development in establishing new turf. If you have a pH higher than 7.5, you may have a phosphorous deficiency in your lawn. A phosphorous deficiency is expressed by slightly stunted plants, blue-green discoloration of older leaves and the purpling of the edges.

Garden soils require a slightly higher level of phosphorous than turf. In garden soils, phosphorous promotes root growth, flower and fruit development and is beneficial to root crops like flowering bulbs.

Organic matter content also will be given and is usually around 1 percent to 2 percent. Organic matter can be added to the soil or lawn in the form of hummus, composted manure or garden compost. Organic matter has numerous beneficial effects on a soil profile. It improves soil structure, increases efficiency of fertilizers, aids in soil productivity, holds moisture and ties up toxic ions. A test result of 3 percent to 6 percent would be great, but 10 percent is ideal.

The best time to apply soil amendments to alter pH, add phosphorous and potassium and incorporate organic matter is in the fall. Follow up six to 12 months later with another soil test. For information on where to get a soil test contact your local extension office.