What Do You Put in Dirt to Bring Up the Acid Level?

pH Simplified

• The pH scale ranges from 0.0 to 14.0, with 7.0 being neutral. Plants such as blueberries and azaleas tend to prefer acidic soils with a pH below 5.5. While you cannot easily change the pH of a huge area, it is simple to create and maintain patches of low pH soil for specific plants. Start acidifying your soil by sending a sample to your local university extension.

Organic Additives

• Amend your garden with organic materials to both acidify the soil and help build soil structure. Acid sphagnum peat moss and cottonseed meal can be used to lower the pH of the soil, while feeding it with additional nutrients. Compost and manure are also effective at acidifying soil, but vary widely in levels of soil nutrients. Organic compounds must be worked into the soil far in advance of planting, so they have time to break down. Retest the soil in early spring, prior to planting.

Other Additives

• Soils requiring simple acidification can be adjusted using many different elements and minerals. Elemental sulfur, iron sulfate, aluminum sulfate and ammonium sulfate are common acidifiers. Iron sulfate reacts much more quickly than some of the other acidifiers, becoming available in as few as three weeks. Use iron sulfate with caution, as it can lead to an excess of salts in the soil. Aluminum sulfate is recommended only for hydrangeas because of its high potential to poison other types of plants. Ammonium sulfate has the potential to add too much nitrogen to the soil, so use it sparingly or as part of an acidifying mixture.

Application of Acidifiers

• The most effective way to amend soil with an acidifying compound is to rototill it into the soil. Rototill down about 12 inches, pulverizing the soil completely. Apply the amendment of your choice to the top of the worked soil at the rate recommended by your soil test. Rototill the amendment until it's completely mixed with the soil. In about three months, send another sample off for testing, and reapply acidifiers if necessary. Ensure you amend a wide enough area for your plants' roots to spread, as the roots of some acid-loving plants are unable to survive outside the acidified zone.