There are various reasons to test your soil.  Lead content determines if kids (or adults) should play near the soil or what kind of fruits or vegetables (if any) should be grown.  Soil testing can also determine what kind of nutrients exist, and, if some are lacking, how to fix the situation.  The process itself is rather simple and anyone can do it, but read through some of the links offered in this article to understand how to do it in a way that works for your situation.

Even in California, most gardening resources recommend sending soil samples to the Soil and Plant Tissue Testing Laboratory at the University of Massachusetts Amherst.  If you know of any local resources for soil testing (e.g. UC Davis), please add detail to this article.

Soil and Plant Tissue Testing Laboratory

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