LIME AND SULFUR ALTER pH
As mentioned, 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 if sulfur were used to lower the reading.
It is difficult to make exact recommendations for amounts of chemicals needed to raise or lower soil pH. Light soils require lesser and heavy soils need greater quantities of acidifying or alkalizing agents. A soil high in organic matter has a different requirement than one low in organics. If the organic matter in the soil has been reduced to humus, the "buffering" effect of the humus usually increases the amount of pH alteration material needed.
The only sensible way to solve the problem is to treat the soil and recheck the pH reading after two weeks, after a month, and again after two months. If not enough material was applied, simply add more. If too much, there is no harm in using sulfur to undo the effects of limestone, and vice-versa.
Here are some suggested amounts:
To raise the pH of light sandy loams one full point (i.e., from 5.5 to 6.5) add 35 pounds of ground limestone to 1,000 square feet. On a medium loam soil, apply 50 pounds, and on a heavy clay loam, 70 pounds. (Either agricultural limestone or the fine chips used for top-dressing driveways can be used.)
To lower the pH of light sandy loams one full point (i.e., from pH 6.0 to 5.0) add 10 pounds of dusting sulfur per 1,000 square feet. In medium loam soil, add 15 pounds, and to heavy clay loam, 20 pounds. (Ordinarily dusting sulfur is perfectly satisfactory; no need to pay a premium for special grades.)
Within the 6.0 to 6.9 range, all foods needed by the majority of shrubs, annuals, perennials and other "average" garden plants are
available in the soil in soluble form, provided the foods are present in the first place. Bacteria thrive and do their vital work better in this pH range, and certain potential poisons, such as aluminum, are locked up so they cannot injure plant roots.