How to Adjust Soil pH

Adjust soil pH slowly over several years.

Plants require soil, air and water to thrive, but all soil's pH is not the same. The pH, or potential hydrogen ions, is the soil's alkalinity or acidity measurement. The pH scale goes from 0 to 14 -- with seven being neutral. Soil with a pH less than seven is acidic and soil with a pH above seven is alkaline. Some plants do well in specific pH levels and will not survive otherwise. You can change soil pH up or down the scale once you know what your soil pH is.

Difficulty:

Moderate

Instructions

Things You'll Need

• Soil test
• Spade
• Hoe
• Rake
• Mask
• Gloves
• Eye protection
• Lime
• Sulfur
• Organic matter

1. Test the soil's pH level with a soil test kit obtained from a garden center, hardware store or nursery. Contact your area cooperative extension office for information about soil testing if you don't want to test the soil yourself.

2. Wear protective gear when applying any type of chemicals to the soil to adjust the pH. This includes gloves, masks and eye protection. Read and follow any instructions included with the products.

3. Add hydrated lime powder to the soil to increase the pH by 1.0 point, depending on your soil type. Use 4 oz. per square yard for sandy soil, 8 oz. for loamy soil and use 12 oz. for clay soil.

4. Add ground sulfur to the soil to decrease the pH by 1.0 point in one season. Add 1.2 oz. per square yard for sandy soil or 3.6 oz. for any other type.

5. Mix the amendments well into the soil ahead of planting using hand garden tools, like a shovel and hoe or a mechanical tiller and then rake the area level for planting. Retest the soil over several seasons and repeat additional pH adjustments as needed until the ideal soil pH is obtained.

Tips & Warnings

• Use organic matter to raise or lower the soil pH. Peat moss, wood chips, mulched leaves, sawdust, well-aged manure or cottonseed meal will lower the pH; use crushed oyster shells, crushed marble, bone meal or hardwood ash to increase the soil pH. Add a layer a few inches thick of the organic matter, then work it well into the soil.

• You can use ground limestone in place of hydrated lime to increase the pH level in your soil. Refer to the package instructions for the amount to use and application procedure to follow.

• Changing your soil's pH typically is a long process that takes place over a number of seasons and should not be rushed. Do not expect quick changes or attempt to alter the pH more than 1.0 point per year. If big adjustments are needed in the pH number, you will most likely need to do several repeat treatments to see results.

References

• The Garden Helper: How to Test and Adjust the Soil pH in your Garden
• Iowa State University Extension; How to Change Your Soil's pH; Eldon Everhart; April 1994
• Organic Gardening Guru: How to Care for Your Soil

Resources

• United States Department of Agricultural: Cooperative Extension System Offices
• National Garden Association: Garden Calculator: Limestone
• National Garden Association: Garden Calculator: Sulfur