Soil testing: A necessity for plant productivity

By Bill Snyder

OSU Extension Program Assistant, Agriculture & Natural Resources

Is your garden ready for the growing season? Does the soil contain the nutrients needed for healthy plant growth? Is it rich in organic matter?

These are important questions that can only be answered by obtaining a soil test from a reliable laboratory.

Soil testing provides a measure of soil’s fertility and ability to support plant growth. A relatively inexpensive analysis provides the amounts of the plant mineral nutrients: phosphorus, potassium, calcium and magnesium. In addition, the soil pH and cation exchange capacity (CEC) are determined. These values indicate how available the nutrients will be for your plants to use.

With a representative soil sample and an accurate test, sound amendment recommendations can help gardeners improve plant quality and productivity.

Why Do I Need to Soil Test?

Soil fertility varies throughout the growing season. Large quantities of mineral nutrients are removed from soils as a result of plant growth and development and the harvesting of crops.

A soil test determines the current soil fertility. It also provides the necessary information needed for the gardener to reach and maintain optimum fertility.

Some plants grow well over a wide range of soil pH, while others grow best within a narrow pH range. Most turf grasses, flowers, ornamental shrubs, vegetables, and fruits grow best in slightly acid soils (pH 6.1 to 6.9). Plants such as rhododendron, azalea, mountain laurel, and blueberries require a more acidic soil to grow well.

A soil test is the only precise way to determine whether the soil is acidic, neutral, or alkaline. The test results will suggest ways to alter the pH to obtain an optimal value for your chosen plants.

The soil test takes the guesswork out of fertilization and is extremely cost effective. It not only eliminates the waste of money spent on unnecessary fertilizers, but also eliminates overuse of fertilizers, helping to protect the environment.

When Do I Soil Test?

Soil samples can be taken in the spring or fall for established sites. For new sites, soil samples can be taken anytime when the soil is workable. Most people conduct their soil tests in the spring. Autumn, however, also can be a great time to take soil tests if you want to avoid the spring rush and suspect a soil pH problem.

Fall soil testing will allow you ample time to apply lime to raise the soil pH. Sulfur or peat moss should be applied in the spring if the soil pH needs to be lowered.

A soil sample is best taken with a soil probe or an auger. Soils should be collected in a clean plastic pail or box. These tools help ensure an equal amount of soil to a definite depth at the sampling site. A spade, knife, or trowel, however, also can be used to take thin slices or sections of soil.

The test results are only as good as the sample taken. It is extremely important to provide a representative sample to the testing lab so that a reliable test and recommendations can be made for the entire area. This can be accomplished by submitting a composite sample.

A good representative composite sample should contain at least 15 cores or slices. Each core or slice should be taken at the same depth and volume at each site. Sample at random in a zigzag pattern over the area and mix the sample together in a clean plastic bucket.

Contact Ohio State University Extension – Mahoning County for instructions and appropriate forms or visit http://mahoning.osu.edu/topics/master-gardener-volunteer-program/plant-and-pest-diagnostic-clinic for testing information.

Adapted from Gary Gao, Joe Boggs and Jim Chatfield, Ohio State University Extension. Details: http://go.osu.edu/soiltesting