Lime is most often used to add calcium to the soil which raises the soil pH. By raising the soil pH, you would be able to place plants in acidic soil that would require a neutral or alkaline soil conditions. Lime also helps open thick clay soil to moisture and air penetration which assists in the decomposition of organic matter.

The only way to be sure if you need to add lime is to have your soil tested. If the pH reading is below 6.0, add lime. If the soil test indicates that your soil is short of calcium and magnesium, add lime. Lime can be added at any time and most recommendations for lime placement is on top or placed very shallow in the soil and then watered in. A good example from the plant world for quick response to lime is the clematis. Quicker growth and plant health can be observed in just 1 season after lime is applied.