Certain garden plants like azaleas, tomatoes and catnip need acidic soil to grow. In most areas, the local soil has a neutral pH of around 7. To make your soil suitable for the plants you love, you need to work slowly. Start the fall before you intend to plant and aim to raise the soil roughly one pH point per season. An abrupt change in pH may shock the soil and kill the plants. Work on raising the pH one point per season and your acid-loving plants will hang on until you get the pH just right.
First, test your soil to determine its exact pH and how much you must lower it. Pick up a pH meter at your local home and garden center or call and see if they offer free pH testing if you bring a soil sample in. Your local county extension office may offer soil testing for a nominal fee if you bring in a sample. Contact them first for instructions on how to collect and label the soil sample.
Apply a 4-inch layer of compost to the soil. Compost acts as a pH buffer. Soil with a pH of 7, for example, will support plants that require a soil pH of 6 or 8. If your soil only needs to be lowered by one point to become acidic, this is all you need to do before spring. Mix the compost into the top 8 inches of the soil and wait until spring to plant. If you need to make your soil more acidic, you’ll need to add more amendments to lower the soil’s pH another point this season.
Mix granular sulfur or peat moss to lower your soil’s pH another point. Add .13oz. of granular sulfur per square foot to lower the pH of sandy soil by one point. Add twice that amount to lower the pH of average or clay soil one point. A 2-inch layer of peat moss will lower any type of soil one pH point. Spread the amendments evenly over the compost. Then mix the compost and amendments into the top 8 inches of the soil.
Once your garden is prepared, it will take the months between fall and spring for the pH to drop down a full point. Once the weather warms, you’re all set to plant. Next year, test the soil again and make any adjustments you need to correct the pH and maintain or lower the level of acidity.