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Improving Vegetable Garden Soil pH

If a test of your vegetable garden soil shows that is too acidic or too alkaline, you can improve the pH. The right soil pH is important for vegetable crop growth and yield.

Most vegetables do best in neutral or slightly acid soil. Gardeners often called acid soil “sour” and alkaline soil “sweet.” Acid or alkaline soil is usually expressed in terms of pH (the degree of acidity or alkalinity) on a scale of 1 to 14. Seven is neutral, below 7 is acid, and above 7 is alkaline.

The availability of nutrients to your plants depends on how acid or alkaline the soil is. A hand-held pH meter will give a reading of the soil’s pH after the prongs are inserted in the soil.

The greatest availability of nutrients–nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, iron, manganese, boron, copper and zinc, and molybdenum—occurs when the soil pH is between 5.5 and 7.5.

Garden lime spread on garden soil
Garden lime spread on garden soil to reduce acidity and balance the soil PH and add calcium.

How to improve soil too acidic

To improve acidic soil, add alkaline material, a process commonly called liming. Ground limestone, specifically calcitic limestone, is the most common material used to raise the soil pH. Ground limestone is slow to break down in the soil and is best added in autumn to improve the soil in time for spring planting. As a general rule, add 4 to 5 pounds of ground limestone per 100 square feet for each unit of pH below 6.5.

Regions with heavy rainfall and forest cover tend to have acidic soil. A soil that tends toward acidic should be limed every third or fourth year in the autumn. Apply lime a month before adding manure or compost to avoid undesirable chemical reactions. It is important to note that soil texture also can affect how additives raise or lower soil pH so if your soil is problematic have it tested and follow the soil lab recommendations.

How to improve soil too alkaline

Regions that are very dry and droughty can have alkaline soil. It is rare that soils are too alkaline, but if that is the case in your garden add sulfur to the soil. Elemental sulfur, Epsom salts, gypsum, and fish emulsion are three sources of sulfur. To correct alkaline soil, add elemental sulfur at the rate of 4 pounds per 100 square feet for each unit of pH above 7. Again, follow soil lab recommendations when adjusting soil pH.

Optimum pH Range for Vegetables

Soil pHVegetable
6-8Asparagus, beet, cabbage, muskmelons
6-7.5Peas, spinach, summer squash
6-7Cauliflower, celery, chives, endive, horseradish, lettuce, onions, radishes, rhubarb
5.5-7.5Corn, pumpkin tomatoes
5.5-6.8Beans, carrots, cucumbers, parsnips, peppers, rutabagas winter squash
5.5-6.5Eggplant, watermelons

Related Articles on Soil pH:

Soil pH and Vegetable Crop Nutrition

Understanding Soil pH

How to Test Your Soil

Adjusting Soil pH

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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