A wide variety of bedding, plants shrubs and trees thrive in or require an acidic soil to grow, fruit and flower at their optimal potential. Acidity is defined by the lower half of the pH scale, ranging from 0 to 7, while alkaline soil ranges from 7 to 14. Soil acidity, or alkalinity, varies widely by region and can be manipulated with organic amendments and some ongoing management of the soil. A soil test is the only tried and true method to determine what kind of soil your garden has. Once you have this baseline information, it can be a powerful tool in tailoring your plant collection to suit your soil or amending your soil with organic material to create the desired acid-rich pH level.
Sphagnum Peat Moss
Lay down and till in a 2-inch-thick blanket of sphagnum moss onto the soil bed. Mix it into the soil at planting time, or top dress the soil around existing plantings. Peat is an effective acidifier, ideal for smaller tree plantings and garden beds, but can be a costly amendment when used over large expanses of soil.
Apply granular sulfur to raise acidity or lower the pH in your soil. Consult the label on the bag to determine application rates, and never exceed 2 pounds of sulfur for every 100 square feet. Lower the application rate by 1/3 if your soil is sandy, and by 1/2 if your soil is heavy with clay. Allow at least a three-month interval between applications of amendments.
Aluminum and Iron Sulfate
Organic aluminum or iron sulfate will each blend into the soil to raise acidity fairly quickly, but must be used in significant amounts. Apply it according to label directions, but do not exceed an application rate of 5 pounds per 100 square feet in one application. More is not better.
Organic Wood Mulch
Lay down a 3-inch-deep blanket of shaved or shredded wood chips over the soil around the plant or bed. Replenish the mulch every year as it degrades and melds into the soil.