Will your garden soil produce well? One of the best items to check is your soil pH or acidity. pH stands for the “potential of hydrogen” and is a scale that indicates whether your soil is acid or alkaline (basic). The pH scale runs from 0 to 14 with 7.0 being neutral. If your pH is below 7.0, it is acid. If it’s above 7.0, it’s alkaline.
The acidity or alkalinity of soil affects various chemical processes and controls how chemicals bind together. For vegetables, a pH between 6.0 and 7.0, slightly acidic, is best. A pH of 6.5 is ideal and allows all the nutrients in your soil to be easily accessed by vegetables. Many fruits also like this pH range; but strawberries like 5.5 to 6.5 and blueberries need 4.5 to 5.5. Hydrangeas will produce blue flowers in acid soil and pink in alkaline soil.
If your pH is outside the desired range of a plant, its roots won’t be able to access nutrients in the soil, and the plant won’t grow well. As a very rough rule of thumb, native plants “up the hill” are adapted to slightly acid soil and natives in the lower foothills are better adapted to neutral or slightly alkaline soil.
Water can also affect the pH of soil. If water comes from a well in certain areas, it may contain dissolved lime. For example, there was a line mine on Lime Kiln Road back in the day. With irrigation over time, dissolved lime will raise the soil pH level. My soil is slightly alkaline due to my well water. Ditch water is generally near neutral.
You may read about putting wood ashes or lime in your soil. Tuolumne County does not have very acid soils like back east, so usually these alkaline additives aren’t helpful here.
If your soil is slightly alkaline like mine, elemental sulfur, aluminum sulfate, peat moss, pine needles or oak leaves incorporated into the soil can lower pH. Aluminum sulfate is fast acting and should be applied carefully. If too much is added, it can result in aluminum toxicity in the soil. The other materials are slower acting and will not cause toxicity. But it is possible to add too much and shoot out the other side of your desired pH range.
If possible, add materials to your garden in fall. I often put about an inch of oak leaves on my vegetable garden each fall to balance my well water’s slight alkalinity. If you want to grow a plant that requires low pH, like blueberries, more would be needed. The advantage of elemental sulfur is that the package will tell you how much to add based on your target pH.
Master Gardeners of Tuolumne County have pH meters and will gladly check a soil sample for you. Bring a soil sample in a baggie to Open Garden Day (first Saturday of the month) at the demonstration garden at Cassina High School or to the master gardener information booth at the Sonora farmer’s market.
