For home gardeners, soil testing is valuable to establish a base line on soil limitations related to pH, salt levels and the need for phosphate and potash fertilizers.
In some gardening situations, soil testing has limited value. For example, testing for nitrogen has limited use for the home gardener because the level constantly changes in response to soil organic matter additions, soil microorganism activity, temperature, moisture levels, leaching and nitrogen consumption by plants and other soil life.
A standard soil test will not identify common garden problems related to overwatering, underwatering, poor soil drainage, soil compaction, diseases, insects, weed competition, environmental disorders, too much shade, poor varieties or simple neglect.
A standard soil test typically will give you baseline information about the following: texture, organic matter, pH, lime, soluble salts, nutrients such as nitrate nitrogen, phosphorus, potassium, and micronutrients such as copper, iron, manganese and zinc.
In the neutral and alkaline soils of Colorado, repeat the test when dramatic changes are made to the soil (such as addition of larger quantities of manure, biosolids or compost that may be high in salts) or approximately every four to eight years to reestablish the base line.
A soil sample may be taken at any time of year, although spring or fall sampling is usually the most convenient.
The results of a test are no better than the quality of the sample sent to the laboratory. The sample must be representative of the yard or garden being considered. Gardeners who try to shortcut the sampling procedure will not receive a reliable result.
Submit a sample for each area that receives different fertilizer and soil management treatments. For example, if the front and back lawn are fertilized the same, the sample should include subsamples taken from each and mixed together. Because vegetable garden areas are managed differently from lawns, the vegetable garden should be sampled separate from the lawn.
Home soil test kits have questionable value. The actual process used in some procedures is based on soil pH. Most home test kits were designed for acid soils, and have questionable accuracy on the alkaline soils of the west.
Soil test kits are available at the Colorado State University Extension office at 25 N. Spruce Avenue, which is open 8-12 a.m. and 1-5 p.m. weekdays.
The cost is $35 per sample and includes a container, instructions on how to take the soil sample and where to mail it. You should also plan on mailing costs.
Additional tests could be run for special needs like lead content or sodium problems.
Information for this article was taken from Colorado Master Gardener GardenNotes #221 and is available online at www.cmg.colostate.edu.
When you have questions, Colorado State University Extension has research-based answers. Get answers to your horticulture questions by visiting ask.extension.org any time day or night. Follow the El Paso County Master Gardeners on facebook.com/ColoradoMasterGardeners.EPC/.