pH is the symbol that represents the alkaline/acid relationship in soil, or in a swimming pool or drinking water for that matter. pH is numbered in a linear scale from 1 to 14. When there is a balance it is called “neutral” soil and is 7 on the pH scale.
Plants cannot take up nutrients from a soil that is too alkaline or too acidic. When soil is out of balance plants are anemic, and vulnerable to pests and diseases. The farmer that learns this too late is disappointed at harvest as well as all along the way. A good pH balance is one of the most important qualities of a good soil.
Most plants will do fairly well in neutral soil, but they really thrive when they are in the soil they prefer. Veggies generally prefer a pH of 6.5 to 7. Many fruit trees and berries prefer a more acidic soil of 5.5 to 6 pH. If plants show signs of deficiencies, first check the pH as the application of fertilizer is futile as the plants can’t take up the nutrients. . Test kits are available from most garden centers or on-line at resources below. Or you can take a soil sample and have it analyzed at your local Cooperative research & Extension Service.
Affecting a change to the soil pH cannot be accomplished immediately; therefore adjusting should be done at least six months before planting. Before adding amendments that may be in themselves acid or alkaline, a gardener’s best start comes in testing the target soil and only then can amendment selection be the most accurate.
Even if the pH of the soil is not optimum, either too acid or too alkaline, most plants will do well in soil amended with plenty of compost or organic matter. Humus or organic matter is the best remedy for alkaline soils, especially peat moss. Coffee grounds are a good addition to your garden or to the compost pile, as are pine needles or even watering with a very diluted solution of vinegar and water. For really high pH levels, you can also adjust pH down with the addition of elemental sulfur, which is an organic substance but is very potent. Because it is used also as a fungicide, some organic gardeners say that it may do harm in large doses by killing off beneficial microorganisms in the soil. So use with caution!
Humus will also neutralize an acid soil in large doses. Another organic method to raising pH is the addition of limestone. Dolomite lime is preferred as it is a natural rock and contains some magnesium along with calcium that is found in ground limestone. Hydrated lime will act faster but is caustic to seeds, seedlings and soil bacteria so should not be used. When adding lime, it must be calculated as it is a potent amendment. Use ½ to 1lb. limestone for each 10 sq. ft. This amount should raise the pH by about 1 pt. Lime should not be added all at once, as adjustments may be needed for your particular site. It should be worked into the soil as deep as possible.
As a general rule, most areas of the country have slightly acid or alkaline soils. The annual addition of organic matter and compost will adjust the soil gradually over the years to a more neutral pH. Testing every year for pH and major nutrients will help you adjust before anything gets too out of whack.