The acid-alkaline balance of a gardening soil, commonly called "pH," determines what nutrients are available to growing plants. Most common flowers, vegetables and shrubs grow best in a fairly neutral-pH soil, rated between 6 and 7 on a scale of 14. Highly alkaline soils, usually present in areas known for large deposits of limestone, need to be acidified to nourish more than a fairly narrow range of plants. This process is not hard, but requires soil testing and may mean large or repeated applications of acidifying soil amendments to make soil hospitable to garden favorites.
Test your soil. This can be done with a commercial test kit or through your local county extension office for a small fee. County extensions are locally based and therefore can give more specific advice about soil conditions and successful treatment in your area than nationally based commercial soil test kits can provide. Testing results include crop specific recommendations to help you change the pH balance of your soil.
Dig in recommended amendments and mix them thoroughly with your garden soil, using your spade or spading fork. Amendments that make soil more acidic include peat moss, ground elemental sulfur and sulfer-containing compounds like aluminum sulfate. Shredded evergreen barks and wood chips, often sold as mulch, also contribute acidity to the soil.
Water amended soil thoroughly, and do not plant until the interval recommended by your county extension or package directions has passed. Like all chemical additions to soil, sulfur compounds need time to work, and tender plant roots can be burned or otherwise damaged by immediate post-application planting.
Retest your soil, especially if your growing plans involve considerable expense. The small cost of retesting is far less than the loss of large shrubs than cannot obtain enough nutrients from the soil to meet their needs.
Repeat acidifying measures as part of your annual soil preparation. Rain, erosion and the nutritional needs of your plants can reduce soil acidity. Keeping soil pH properly balanced cannot be done as a one-time job, but your ongoing efforts will be repaid by a thriving garden.