The Part-time Gardener #2: What’s a soil test, and do I need one for my home garden?

When I first started home gardening, at no point did it ever cross my mind that I should get a soil test done before planting.  I thought people just plunked their seeds or transplants into whatever soil they had in their yard. This might work in some parts of the country, but apparently it’s not the best idea here in Southern California. As I learned more about urban agriculture, I realized that a soil test should be one of the first steps in planning ANY garden.  Especially if your garden is like mine:

1) Located in an urban area.
2) You don’t know the full history of your land. (Also known as site history. For example, was it ever a site for manufacturing, chemical industries, heavy pesticide use, etc.)
3) You plan to grow edibles.

What can a soil test tell me?

Potential human health impacts
All soils naturally contain some trace elements, and some of them are essential for maintaining life on this planet. In a world without humans, we wouldn’t necessarily have to worry about them. However, in any place that has been subjected to human activity, we should be aware of the potential for elevated levels of trace elements.

A soil test can tell you if elements called heavy metals such as lead, cadmium and arsenic are present at worrisome levels. These metals can be released into the air through, for example, vehicle exhaust, power plants or homes with lead-based paint.  The particles can eventually land in your garden soil. (Source: Heavy Metals and Urban Gardens) Plants can absorb these metals, but it is usually in relatively small amounts. The real danger to humans is more likely through swallowing or inhaling contaminated soil or dust.

Soil health
Aside from learning about potentially harmful metals in your soil, you can also gain some insight into basic nutrient levels through a soil test.  This is critical information, since nutrients can dictate how your plants fare. For example, the most common nutritional problems in California are related to deficiencies of nitrogen, phosphorous, potassium, zinc and iron, plus toxicities due to excesses in boron, chloride and sodium. A soil test will reveal what kind of specific issues may be present in your case.  The test will also cover pH. Most crops grow best when the pH of the soil is between 5.5 and 7.5.  (Source: California Master Gardener Handbook, 2nd Edition, Pg. 62-63).

So do I need a soil test? Which one should I get?

According to University of California Agriculture and Natural Resources, a soil test is recommended for any type of urban agriculture. If you want to err on the safe side, this is definitely the way to go.

These days, it is also fairly simple to get a test done. A commercial laboratory can preform a diagnostic test using a provided sample for ~$50.  To make our lives even easier, the University of California Agriculture and Natural Resources has a drummed up a List of Soil Testing Laboratories.

In my case, I decided to get a basic soil analysis as well as a heavy metals test through UMass Extension.  I’ll cover my experience actually doing the test in my next blog!

With hands to soil,

Erin

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