What Neutralizes Lime?

Lime

• Lime is a naturally occurring substance that makes soil alkaline, which many plants tolerate. If your soil is too alkaline, meaning its pH level is too high, then several substances can be used to lower its pH level. Incorporating 1 or 2 cubic feet of sphagnum peat per planting hole before putting plants in the ground is a good start. It can provide plants an acidic environment for a while but probably won’t have lasting results. Substances that have longer-lasting effects are elemental sulfur, sulfates and ammonium fertilizers.

Elemental Sulfur

• One of the best substances for soil acidification is elemental sulfur, but it works quite slowly. Seeing even a small change in pH can take months. The amount of elemental sulfur to use depends on the soil's type, the soil's starting pH level and the desired ending pH level. Clay soil requires more sulfur than loam soil, and loam requires more than sand. Lowering soil's pH level a lot requires the incorporation of more sulfur than the amount needed to lower the pH level a little. For example, about 14 pounds of elemental sulfur is needed to lower 1,000 square feet of silt loam from a pH level of 7.5 to 6.5.

Sulfates

• Both iron and aluminum sulfate lower the pH of soil, but aluminum is dangerous to use because adding too much of it to soil risks poisoning plants. It is safer to stick with iron, which works quickly, reacting in only three or four weeks. Do not apply more than 9 pounds of iron per 100 square feet of soil in a single application, however. Because even a moderate reduction in pH -- from 7.5 to 6.5, for instance -- requires using 12 1/2 pounds of iron per 100 square feet of soil, splitting the iron amount into two parts and applying one part in spring and the other part in fall may be necessary instead of applying the entire amount at one time.

Ammonium Fertilizers

• Nitrogen-based fertilizers that contain ammonium (NH4) also lower soil's pH level. When you buy a fertilizer, check its package information for compounds such as ammonium nitrate, urea, ammonium phosphate and ammonium sulfate. The fertilizer is neither a quick way to lower soil pH nor a drastic way. Don't expect the soil's pH level to drop by more than 0.4 in two years. For instance, 3 1/2 pounds of ammonium applied annually to 1,000 square feet of soil lowers the soil's pH by a maximum of 0.2 units per year.