Lowering Soil pH

Lowering soil pH can be critical for the garden plants you want to thrive.

Grandfather knew nothing about the pH scale. Even if the theory had been invented in his day he probably would have called it "book rubbish." Nevertheless, he knew enough about soil reaction to spread load after load of marl or ground limestone on his fields every third or fourth year. He did this to "make the soil sweet and keep the land up," as he phrased it. He knew that when the lime began to "dissolve" his crops grew better and he made more money. Too, the soil would be in better "tilth" and would turn more easily under the plow.

In this simple but important chore he was repeating what generations of farmers since Roman days had done before him - overcoming a too-acid soil with lime. Although ignorant of chemistry, he knew a soil was "sour" if sorrel grew well, or "sweet" if clover and alfalfa thrived. Sometimes, if in doubt about the time to lime, he would touch a grain or two of soil to his tongue. If it had a soapy taste he knew it had some lime in it but if it tasted acid or sour he laid plans to supply the missing element. Plant growth improvements seemed so directly connected with these applications that he thought of limestone as "rock manure," supplying something the plants had to have. Today we know that while lime does supply calcium, usually the indirect effects are much more important than the direct. This in no way detracts from the soundness of grandfather's methods - he got results.

You need know little more than he did in order to use pH correctly. True, you have the help of modern soil testing equipment much more accurate than the human tongue, and you can regulate the actual pH range more accurately. But without any scientific background you can correctly apply lime and fertilizer on acid soils, or if your soil is too alkaline you can apply sulfur for lowering soil pH.

Lowering soil pH can be important when growing all but a limited number of plants (acid-loving species like blueberries, mountain laurel [kalmia], hollies, camellias, azaleas and rhododendrons). You should strive for a soil reaction somewhere between 6.0 and 6.9. Ordinarily, a reading of 7.3 is as high as your garden soil should be allowed to go if you are growing the usual mixture of annuals, perennials, vegetables and shrubs. For many plants, even this is a trifle high. Growth would be better with the use of sulfur to lower soil pH.