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Farm Advisor: Soil pH Is Important To Your Plants

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{b” >This article was provided to by Calaveras County Farm Advisor Ken Churches.{/b” >

San Andreas, CA — Soil pH can make a big difference to the plants in your garden. Scientifically speaking, pH measures the concentration of hydrogen ions in soil solution. It is measured on a scale from 0 to 14, where values below 7 indicate acidic soil, and those above 7 indicate basic or alkaline soil. Each unit change is a 10-fold difference in the concentration of hydrogen. That means if your soil pH is 6.0 and your neighbor´s soil pH is 5.0, your neighbor´s soil pH is 10 times more acidic than yours.

As soil pH decreases, the solubility of iron, zinc, manganese and aluminum increases. The concentration of some of these metals can reach levels that are toxic to some plants. Alfalfa, garlic and many garden vegetables are particularly sensitive, whereas blueberries and rhododendrons are quite tolerant. Standard soil tests can determine the pH level of your soil. If it is too acidic, the addition of lime can help raise the pH.

Coffee is a good example for understanding. With a pH of about 5.5, coffee can be too acidic for some people. How do you reduce the acidity of coffee? You add cream. The action of cream in coffee is the same as adding lime to soil. And just as you would need to stir the cream into the coffee, so you need to mix the lime into the soil before planting. The goal of putting lime in your garden or cream in your coffee is not to neutralize all hydrogen or raise the pH to 7, rather it is to reduce acidity to a tolerable level.

The pH of a liming material is not as important as its ability to combine with hydrogen, the primary component of soil acidity. Just as an oyster shell in your coffee cup would do little to neutralize the acid, so some materials react differently with the hydrogen in the soil. Effective liming agents such as calcium carbonate (agricultural lime) or dolomitic lime, bind with hydrogen and remove it from soil solution, which in turn reduces acidity. Inexpensive soil pH test kits are readily available at most nursery supply stores. Test your garden soil before planting this year to insure a quality crop.

Please contact the Farm Advisor´s office at or call (209) 754-6477 with your agricultural questions.

Ken Churches is the county Farm Advisor and director for the University of California Cooperative Extension.