How to Fix Acidic Soil Organically

A pair of gardening gloves and gardening tools laying on freshly worked soil.
What You'll Need
Soil pH testing kit
Garden shovel
Sample containers
Ground calcite limestone
Wood ashes
Organic compost

Many vegetables, such as asparagus, celery, and lettuce prefer a nearly-alkaline soil, as do flowers like chrysanthemums, sweet peas, dahlias, and tulips. Follow these guidelines to raise the pH of your garden soil from acidic to more alkaline.

Step 1 - Test the Soil pH at Various Places in Your Garden

Use the soil pH testing kit to get an idea of the average pH of your garden soil. Check the clay and sand content of your soil as well. Sandy soils tend to be more acid to begin with, whereas clay soils can be highly alkaline. Do this testing in the fall or before you plant in the spring. If you find your pH too low for your intended crop, raise the pH to lower the acidity.

TIP: Our expert gardening advisor, Karen Thurber notes, "Home pH test kits can be unreliable and inexact. Instead, have a soil test done by your local county or state extension service. This will provide you with a clear picture of your soil pH and soil type. It will also include recommendations of amendments that will benefit the soil."

Step 2 - Prepare the Soil for Organic Ingredients

Till the soil thoroughly with a rototiller. Add the high-pH organic compost and till it so the soil and compost are fully blended.

Step 3 - Adjust the pH

ashes from a fire in an area of lawn

When raising the pH of your soil, there are a few additives to choose from. Choosing the one that is right for you will depend on the size of your garden, and what is available to you. For home gardens, the most commonly used pH raising additives are calcite limestone or dolomite limestone.

Calcite Limestone - Add the ground calcite limestone, a naturally occurring material, to the soil at the ratio of five pounds per 100 square feet of garden soil. Dolomite limestone can also be used.

TIP: Karen adds, "The application rate of lime will depend on the type of soil and the initial pH. Refer to your soil test results and recommendations for application rates."

Hydrated Lime - Hydrated lime is a solution of quicklime and water. The water added makes a solution of calcium hydroxide out of the calcium carbonate. Adding hydrated lime to garden soil alters its pH to an alkaline level quickly, but can also result in soil that is too alkaline, if applied improperly.

TIP: Karen warns you, "Use caution when working with hydrated lime. It is corrosive and can burn your skin. Wear protective clothing, dust mask, boots, gloves,

and goggles. Ground or pelletized lime is safer and easier to use."

Wood Ashes - Ensure your wood ashes come from untreated, natural wood. Add wood ashes at twice the rate of calcite limestone, as wood ash contains 50 per cent of the calcium carbonate that makes soil alkaline, compared to limestone. Wood ash is a useful and inexpensive way to raise the pH of a very small garden area that is isolated from the main garden. Natural wood ashes also contain potash, a source of potassium, an important plant nutrient. Potassium helps bud, flower, and fruit formation in plants.

Step 4 - Maintain the New Soil pH

Rendering soil more alkaline may take several growing seasons. As you adjust the soil pH toward more alkaline values, grow plants in it that prefer an alkaline soil, and plow them under for two seasons. These plants will increase the nitrogen levels in the soil, so what you plant will engage in more vigorous photosynthesis. Continue to add more organic compost every season in the fall and check the pH before planting each year.