Soil testing can provide information on your soils texture, pH, salinity and the level of essential plant nutrients and fertility. This information may be very useful if you are starting a new garden in an area where plants have not been grown before.
Soil testing may also help you find out why plants are not growing well in an existing garden. A soil test is not always necessary, however, and it will not tell you if poor plant growth is caused by pests or diseases, improper irrigation or poor cultural practices, such as planting at the wrong time of year.
One of the most useful soil tests is the measurement of soil pH. The test will tell you if your soil is too alkaline or acidic and if corrective measures are needed. A lab can measure soil pH for you or you can do it yourself. A simple pH meter and test kit are available at local nurseries or from mail order companies.
Commercial soil testing services are available through some nurseries and garden centers. You can also find analytical laboratories listed in the phone directory. Soil testing is not performed by the County or State Agriculture Department, or the University of California.
You will only get good information from a soil test if you collect a good sample. To collect soil for testing, dig a small hole 6-8 inches deep with a trough and collect a thin slice of soil from one side of the hole. Put the soil in a bucket and collect more samples from several locations in the garden. Mix the samples together to produce a representative sample from your garden. If you use a commercial testing lab, ask if they will provide a report to help you interpret the results of your soil test. Also ask if they provide recommendations on how to correct soil problems.