all the dirt on soil

To really know what creates healthy plants, you need to test your soil

by Lynn Snyder

Whether you’ve just moved into a new home, or you’ve owned your home for many years, horticulture experts suggest a soil test could be in order.

If you’ve never tested your soil, you really don’t have a baseline of knowledge on which to form your gardening and lawn maintenance decisions, according to Tim Malinich, an Ohio State University Extension agent based in Cuyahoga County.

Gardeners should test their soil at least every three years to determine what nutrients the soil might be lacking. For vegetable production, you might consider a soil test every year.

Soil Types
According to the Ohio State University Extension fact sheet, “Improving Soils for Vegetable Gardening,” the best type of soil is sandy loam soil, well supplied with organic matter. Unfortunately, many gardens do not contain such soils.

Very coarse, sandy soils dry out rapidly and are difficult to maintain at a high level of fertility. Clay soils are hard to work and usually remain wet until late in the spring. These soils are often yellow or dark brown and sticky when wet; or grayish in color where drainage is poor. Clay soils tend to form a hard crust after a heavy rain and become so compacted that the plant's root system is deprived of essential oxygen required for growth.

If you are interested in knowing your soil type, Malinich said your county OSU Extension office should have a soil map of your county. He also said you might be able to find your soil map on the Internet.

Maurice Watson, a soil specialist in the department of natural resources at the Ohio Agricultural Research and Development Center, describes soil as the thin skin around the earth, made from the weathering of rocks. Soil is a living system composed of layers of silt, sand, clay and microorganisms. “It is important to maintain organic material as best as you can,” he said.

The fact sheet goes on to say most soil nutrients are readily available when soil pH is at 6.5. When pH rises above this value, nutrient elements such as phosphorus, iron, manganese, copper and zinc will become less available. When soil pH drops below 6.5, manganese can reach a toxicity level for some sensitive plants. A soil test will determine the current fertility status. It also provides the necessary information needed to maintain the optimum fertility year after year.

Performing the test
According to Malinich, homes in urban and suburban areas tend to suffer from soil compaction. During the home construction process, heavy soils are brought to the surface and are layered on top of the topsoil.

“The topsoil gets buried,” he said. “It changes once construction happens. It doesn’t make the soil what it used to be.” This leads to faulty nutrient levels making it “even more important to soil test for lawns and gardens,” he said.

For the most reliable results, it is best to avoid the soil tests sold at garden centers. Instead, work with your local OSU Extension office and send soil samples away to a credible lab. Malinich said there is a great deal of variance with garden center soil tests and it is difficult to know how to interpret the results or what to do with them.

If you work with your local Extension office, most counties can recommend a lab it has worked with in the past. A basic test should cost $10 or less, he said. “The good part about this is when it comes back, it’s not just results of the amount of phosphorous, potassium, pH (present in your soil), but they come back with recommendations,” he said. This means a gardener would know what steps to take to improve soil quality.

Testing origins
Watson said modern soil testing has been around since the 1940s when farmers first started using soil testing as a technique to improve yields. The idea that soil testing could help correct nutrient deficiencies to get optimum crop production came to light in the 1970s. He noted the economic factor to soil testing, too: Adding nutrients is a cost of production. Farmers don’t want to add more nutrients to the soil than are needed.

The same can be said of home gardeners, who he said tend to over apply nutrients to their gardens and lawns. If the levels are too high, it can actually hurt gardens. “If you don’t need it, don’t add it,” he said.

Good soil is more than just proper nutrient levels, it’s also proper drainage, moisture level, texture and structure, plus avoiding the problem of erosion. Home gardeners and farmers can modify all of these components as well.

Help through OSU Extension
A wealth of gardening information is available through county Extension offices and the Ohio State University Web site. Visit ohioline.osu.edu for more information.

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