Anchorage Daily News

Q. Where can I get my soil tested, and how should I collect the sample?

A. You can have your soil tested by the lab at the UAF Agricultural & Forestry Experiment Station in Palmer, but first ask yourself why you want to test. We've all been taught that good gardeners test their soil, but because the price of the standard test is $40, I find myself quizzing gardeners to see if they have a problem before I recommend testing.

The standard analysis done by the Palmer lab includes pH, nitrogen, phosphorus and potassium. It's a good test done with research-grade equipment. In fact, at last week's Anchorage Master Gardeners meeting, Jeff Smeenk, commercial horticulture specialist with the UAF Cooperative Extension Service, compared lab results with numerous home soil test kits and meters.

One of the inexpensive pH meters gave a reading that was two levels different from the lab test. Another didn't work at all. The colormetric pH tests, in which you mix a magic capsule or solution with your sample, weren't much better.

If you decide to purchase a pH meter, I'd suggest one that can be calibrated so you'll know your reading is accurate. There are also greenhouses in Anchorage that test soil pH as a public service.

The home test kits for nitrogen, phosphorus and potassium didn't work either. In some cases it was impossible to match the color of the sample to a color on the chart of the soil test package. In others, the readings didn't coincide with the results from the lab and tested high when the lab indicated nutrients to be low.

To collect a representative sample for an average-size garden, I suggest taking at least five sub-samples. For vegetables and flowers, dig a hole 8 inches deep and, from the side of the hole, take a sliver of soil and put it into a bag. Do this in five locations and shake up the soil to mix it thoroughly.

The UAF soil testing lab in Palmer needs 1 to 2 cups of soil to run a test. For lawns, sampling 4 inches deep should be adequate, but before you take your sample, pull off the plug of grass on top.

Soil test packets can be obtained from your local UAF Cooperative Extension Service office. In Anchorage, we are at 2221 E. Northern Lights Blvd., behind Medical Park at Northern Lights and Lake Otis Parkway. The packet contains an information sheet, a bag for your sample and an envelop you can use to mail your sample and payment to the lab. It takes about two weeks to receive your results. Your lime and fertilizer recommendation come from Cooperative Extension.

If you've already planted or recently amended your soil, I suggest not testing at this time. Watch to see how your plants grow this summer to determine if you need to add more fertilizer.

If you are interested in testing for soil microbial activity, the National Sustainable Agriculture Information Service maintains a long list of laboratories at attra.ncat.org/attra-pub/soil-lab.html#introduction.

Julie Riley is the Anchorage horticulture agent for the University of Alaska Fairbanks Cooperative Extension Service.

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