Gardeners should put lime on their gardens when the pH level falls below 6.0. Plants grow best in a slightly acidic environment, with a pH between 6.0 and 6.5, and lime helps to raise the soil pH to an appropriate level.
Before adding lime to his garden, a gardener should first test the soil using a soil test to ensure that the pH levels are low enough for lime. Adding lime to soil that already has a pH of 6.5 can harm plants by preventing nutrients from being available. Plants in soil with a too high pH typically have yellow leaves and stunted growth.