Definition of Alkaline Soil

pH

On a scale of 0 to 14, pH is a measurement of the level of hydrogen ions in relationship to hydroxyl ions that exist within soil.

Alkaline Soil

Soil that is alkaline has a pH reading above 7.0.

Acidic Soil

Acidic soil measures below 7.0 on the pH scale.

Neutral Soil

Soil with a reading of 7.0 has neutral pH. Most plants prefer soil at or near neutral.

Alkaline soil, sometimes referred to as "sweet" soil, registers above 7.0 on the pH scale. Unlike acidic soil, which has a pH value of less than 7.0, alkaline soil contains more hydroxyl ions than hydrogen ions.

The Importance of pH

Soil pH is important because it affects the availability of nutrients in the soil. If soil is too alkaline or too acidic, many nutrients that plants require for optimum growth—or even survival—are not accessible to them.

The majority of plants grow best in relatively neutral soil that falls within a range of 6-7.5 pH, a little above or below 7.0. At these levels, the essential nutrients most plants need are most available to them. However, just as some plants prefer acidic soil, a number of plants grow best in soil that is a bit alkaline. (See the chart below.)

The Law of Tolerance

In ecology, the law of tolerance refers to a plant's ability to live in a broad range of pH values.

Plants with high tolerance may perform poorly in soil with pH values outside their preferred range, but they won't die.

Some plants, most notably weeds and other invasive types, have a very high tolerance for a wide range of pH levels (Foerster 17).

To determine soil pH, run a soil test. If your soil is too alkaline to suit the plants you're growing, you can increase its acidity by adding organic matter. Over time, organic material, such as sphagnum peat moss, composted manure, leaf mold and other natural amendments, tends to bring soil pH values at or near neutral (7.0).

Although slow-acting, granular sulfur is an inexpensive amendment that will lower soil pH. Elemental sulfur, aluminum sulfate and iron sulfate will also decrease soil alkalinity (Everhart).

Everhart, Eldon. "How to Change Your Soil's pH." Horticulture & Home Pest News. Iowa State University Extension and Outreach. 6 April 1994. Web. 10 October 2012.

Foerster, John. "Ecology." Maryland Master Gardener Handbook. University of Maryland, 2008: 5-20. Print.

The Dirt Farmer has been an active gardener for over 30 years.

She first began gardening alongside her grandfather on her parents' farm. Together, they would plant acres of vegetable gardens, setting tomato, eggplant and bell pepper plants; sowing row after row of beans and corn; and building up mounds of soil for white squash, pumpkin, cantaloupe and potatoes.

Today, The Dirt Farmer gardens at home, volunteers at community gardens and continues to learn about gardening through the MD Master Gardener program.

Copyright © 2012 by The Dirt Farmer. All rights reserved.