You do not need a soil test to tell you organic matter is good for your garden. Perhaps the biggest landscape mistake is not addressing the health of the soil. With all the soil tests that I have read in the last five years of being an educator, tests find around 1 to 2 percent organic matter.
Experts would prefer this number be at 10 percent. Adding organic matter in the form of compost can prevent nutrients from leaching, improve soil texture for root growth and can prevent some diseases in the landscape.