How to Reduce pH for Growing Potatoes

Test the soil at a university extension office or at another reputable testing site to be certain of a correct, specific pH reading before attempting to reduce pH. Significantly lowering some highly alkaline soils, such as soils formed from limestone, with its high calcium levels, or soil contaminated by certain construction materials, is impossible. Testing and analyzing why the soil is alkaline is key to attempting to lower pH.

Apply peat moss or animal manure once or twice a year to lower pH. Organic materials like these decompose and need to be replaced.

Add soil amendments with ammonium sulfate, iron sulfate or aluminum sulfate to lower pH. Look for these sulfate materials in fertilizers classified for “acid-loving” plants in your garden store.

Add sulfur for a faster fix, but prepare for a more complicated application process. Sulfur must be mixed with moist, aerated, warm soil to create the necessary chemical reaction to lower pH. It’s also temporary and will affect only the immediate application area.

Measure sulfur applications carefully to avoid damaging plants. Use 1.5 pounds of sulfur for 100 square feet of soil to lower pH by 1 unit. Too much sulfur or too many applications can hurt plants.