Have your soil tested
To determine the exact components of your soil, you can do any of the following three things:
You can purchase a soil test kit at many retail garden centers and do the testing yourself
Source: HortTechnology 17:358-362 (2007)
Or you can send a soil sample to a testing laboratory
Or you can visit Orange County Farm Supply in Orange and drop off a sample; be sure to call them at (714) 978-6500 first to find out how to take a sample.
Click here for an introduction to amending soils from Colorado State University.