PH refers to whether soil is acidic or alkaline. On a pH scale of 0 to 14, neutral is 7; above is alkaline and below acidic. The Iowa State University Extension explains that soil pH affects the availability of nutrients in the soil. Highly acidic soil can have deficiencies of nitrogen, phosphorus, potassium or zinc. Adjusting the acidity of garden soil is not a quick process and requires repeat testing and possible repeat amending. If you are going to add plants that need akaline soil in the spring, begin to amend the acidic soil in the fall.
Dig up the garden soil to at least 8 inches deep; be careful not to damage plant roots in established gardens. If you are unable to dig to 8 inches, dig to at least 4 inches. Test the garden soil, using a soil-testing kit. Repeat this test on several sections of the garden. Alternately, take soil samples to the local extension agency.
Test the garden soil, using a soil-testing kit. Repeat this test on several sections of the garden. Alternately, take soil samples to the local extension agency.
Incorporate hydrated lime or lime to a depth of 8 inches to raise the pH. Mix well. Loam or clay soils will require more lime than sandy soils.
Retest the soil in a month. Add more lime if the pH is not at the desired level. Depending upon how much the pH needs to be changed, this process might take more than a year. According to the Virginia Cooprerative Extention at Virginia Tech, "Lime incorporated into the soil will increase the pH to the target level (i.e., 6.5) in about two years."