A note about soil testing: if your plants are growing well, you may not have to worry about it. However, from the Master Gardener Handbook 2nd Ed.: "because most nutritional disorders of plants are difficult to diagnose from visual symptoms alone, tissue and soil analysis are often needed as well. In some instances, plants may not show symptoms of nutritional deficiencies until severe stress has occurred."
Soil testing options
The UC Master Gardeners do not offer a soil testing service. If you're interested in learning more about the composition of your soil, you should contact a commercial laboratory. Inexpensive do-it-yourself soil test kits are available but they are not very accurate. Commercial analytical labs are more expensive but provide more accurate results.
Testing services may include the following. Please contact the lab for specific services.
- Soil testing for pH, salts, nutrients, trace elements
- Water testing for biological and mineral components
- Plant pathology testing for diseases and nutrient deficiencies.
UCCE Sonoma has a list of Northern California laboratories. Many universities also have testing laboratories that can be used even if they are located out of state (a good starting point is searching for "soil testing services" on educational websites).
After receiving results from a commercial soil test, this soil test interpretation guide from the Oregon State University Extension may be helpful to interpret it.