Testing on your own or sending a sample to the tab

Home test kits give you a basic pH reading and an estimation of the major nutrients in your soil. Nurseries and garden centers sell test kits ranging from extremely simple to elaborate. The more sophisticated tests cost more but give you more accurate results.

You can also send a soil sample to a lab for testing. The nutrient level and pH test results are more accurate and detailed than those provided by home kits. In addition, testing labs can look for things that home kits can't, such as organic matter and micronutrients, as well as heavy metals and other industrial residues. (Soils near heavily traveled roads or on old industrial sites can contain chemicals and metals that you may want to know about before planting a vegetable garden.)

Lab reports also offer specific recommendations about which nutrients to add to your soil (and in what quantity) for your plants' optimum growth. Many state-university extension services offer free or low-cost soil test kits. To find the extension office nearest you, consult the U.S. Department of Agriculture's Cooperative State Research, Education, and Extension Service Web site at www.csrees.usda.gov/Extension.

The soil ecosystem changes constantly, so a soil test is just a snapshot of your soil at the time you gather the sample. Although the soil pH and many nutrient levels are relatively stable, other nutrient levels (such as nitrogen) can change forms depending on precipitation, temperature, and crop cover. Use your soil test results as guidelines, but focus on building a healthy ecosystem rather than on simply adding nutrients.

Your soil's pH results

Most plants grow best in a pH range between 6 and 7, with 6.5 to 6.8 considered ideal. Some plants, however, such as blueberries and rhododendrons, like a highly acid soil (pH below 5), so you may need to adjust the pH to individual plants.

Generally, soils in areas with low rainfall often are alkaline; those in highrainfall areas usually are acidic because rain leaches calcium from the soil. To paint a broad stroke, if you live east of the Mississippi River, you probably have acidic soil; if you live in the arid Western states, your soil is probably alkaline. Testing your soil to be sure is a good idea, however.

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Nutrient test results

A soil test also shows the quantities of soil nutrients that are available to plants, especially the three nutrients that plants use in the greatest amounts: nitrogen, phosphorus, and potassium. Soils also contain many other nutrients, such as magnesium and calcium, that plants need in smaller amounts. If any nutrient is insufficient, plants don't grow to their maximum potential.

Soil test recommendations may not follow organic principles. They may suggest, for example, that you add specific synthetic fertilizers to boost certain nutrient levels. You may need to look for organic alternatives to provide these nutrients.

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