While most plants can survive in a wide range of pH levels, there are optimal pH levels for plant growth. To make the most of your garden, it helps to be aware of your soil's pH level. Organic matter, fertilizer and even excessive rainfall can increase soil acidity. However, you can add lime or wood ash to your soil as a counter measure.
Test the pH level of your soil to determine how acidic it is. This test is best done in the fall to allow time for any soil amendments you apply to take affect before planting season. You can use litmus paper or purchase a pH testing kit from a garden center. Any number less than seven is acidic; any number greater than seven is alkaline. Most plants prefer a pH of 6.0 to 6.5---which is slightly acidic. At this pH, more soil nutrients are available to the growing plant.
Determine the amount of clay in your soil. The higher the clay content, the more difficult it is to lower the soil's acidity. Sandy soil is easily made less acidic. Also consider the size of the area you are working with and the type of crop you plan to grow when determining how much lime to add.
Choose a liming material. While a granulated or pellet form of lime may be easier to spread, pulverized lime is finely ground and more easily absorbed by the soil. Some of the lime products available are produced from natural shell deposits, sugar beet by-product, slag, and limestone. An alternative to lime is wood ash.
Apply lime using a fertilizer spreader in the fall or winter---well ahead of planting season. This will allow plenty of time for the lime to be absorbed by the soil and take effect. Apply the lime when the soil is moist---not dry---for optimal results. Too much lime can scorch the roots of plants, so take care to follow package instructions. If you use wood ash, it may need to be added more than once---in thin layers---to have the desired effect.
Work lime or wood ash into the soil with a tiller or pitchfork for faster, more efficient absorption.