Soil acidity and its importance to plants is not a topic that enthralls many of us. Other than real soil scientists, people would rather know about the hottest new variety of plant or how to get rid of some bad bug. I like to keep the topics of acid and alkaline soils and lime real simple. Otherwise I have to look it all up.

For starters, most soil in the southeast U.S. is acidic for good reasons. Lots of rain and warm temperatures cause the chemical reactions within soil to be faster and more intense than in dryer, cooler climates. Other than the few areas of limestone formations, our native soil came from rock minerals that produce acid when they react with water.

Another thing that naturally makes soil more acid is the decomposition of organic matter. That one goes along with climate because the more rain and warmth, the more plant growth there is to decompose.

There now, an oversimplification if there ever was one and I’m going to leave it that way.

We measure and express acidity as “pH.” And that really does stand for something; potential Hydrogen. The pH scale is from 0 to 14 with 7 being neutral, above 7 alkaline and below 7 acidic. Most plants we grow here do best in a slightly acid soil with a pH between 6 and 7. The local exceptions are those few species that actually grow better in more acidic soil. They include azalea, blueberry, and centipede grass. Sometimes I tell people the likely reason their blueberry plants are not doing well is because their dirt is too good.

Even most newbie gardeners know lime is used to raise soil pH to a plant-happy level. The detailed chemical explanation is beyond me other than to say lime contains lots of calcium and calcium is one of the most alkaline of elements. A good off-season chore for gardeners, as well as farmers, is applying lime where it is needed.

And it is not just a matter of using up some otherwise idle time. Lime can be put out any day of the year. But since the good that lime does takes a while to happen, the sooner the better. If vegetable garden soil has become too acidic, adding lime now will have more effect on the 2013 crop than waiting until spring.

And who would guess that I will emphasize the only way to know whether or not lime is needed is to test the soil? A soil test needs to come with results in pH, not just the litmus paper test of acid versus alkaline. A pH of 6.5 is acid, but 5.5 is 10 times more acidic and 4.5 is 100 times more acidic.

One final point now that fireplace season is here; wood ashes are very alkaline. Ashes added to soil raise the pH similar to liming. So never pile ashes around a plant. Your grandpa might have scattered ashes on his garden. He didn’t pile them.

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Terry Rector writes for the Warren County Soil and Water Conservation District, 601-636-7679 ext. 3.