Soil pH: The Secret to Happy, Healthy Plants

If you’ve done everything you can think of to help an ailing plant, but nothing works, it might be a pH imbalance in the soil. The soil’s degree of acidity or alkalinity (pH) is critical to healthy plant growth.

In fact, many plant problems aren’t caused by insects, disease or lack of nutrients. Instead, it’s a soil that’s too alkaline or acidic. If the pH is too low or too high, many nutrients can’t be released to plants. That means you can be fertilizing as instructed, but the plants never get the nutrients from that fertilizer.

A common example of a nutrient that can be lost to soil pH imbalance is phosphorus. This nutrient needs a pH near neutral to become available to plants. Without phosphorus, plants aren’t able to photosynthesize, root or flower.

Another common problem is chlorosis with acid-loving plants like citrus. Though chlorosis is officially due to iron deficiency in a plant, it’s not always a lack of iron in the soil that causes this ailment. Rather, it’s the fact that the soil is too alkaline and unable to release the iron to the plants. Acidic soil is best for absorbing iron.

Other important nutrients that can get tied up because of a soil pH imbalance include magnesium, nitrogen and calcium. Even soil microorganisms, like fungi and bacteria, can get caught up in a pH imbalance. And that means less healthy soil overall.

Tip burn in plants can also be a result of a pH imbalance.

About Soil pH

Soil pH runs on a scale of acidity to alkalinity, with a range of 0 to 14. The most common levels are found between 4 and 8.

With soil pH, 7 is neutral. Any readings above 7 are considered alkaline, and any readings below 7 are considered acidic. Many plants thrive between 6-6.5. Of course, there are exceptions. There are acid-loving plants, like azalea and citrus, that prefer even more acidic conditions. And then there are alkaline-loving plants, such as nasturtium.

If a point doesn’t sound like much, think again. Each point up or down on the scale signifies a tenfold increase or decrease in the soil alkalinity or acidity.

Certain areas of the country tend to be either alkaline or acidic. For instance, the west and southwest often have alkaline soil, while the Pacific Northwest, east and southeast tend to have acidic soil.

Test Your Soil

If you’re having trouble growing a plant, test the soil pH. This is easily done with a testing kit. Such kits generally use powders that you mix with water and soil. Then you consult a color chart, which will indicate the pH of the soil. You can also use a meter, but keep in mind that the less expensive models may not be accurate. These meters require calibration to work properly.

Take a few samples of the soil you’re testing from different areas. In the ground, go down two to six inches deep. In containers, go down one to two inches.

Use distilled water when doing a soil test, as it is neutral.

It’s good to test throughout the year, because soil pH changes depending on soil temperature. Keep in mind, as well, that areas near concrete will tend to be more alkaline. Fertilizer also alters soil pH, as does your tap water.

Adjust pH as Needed

If your soil pH needs adjusting, it can be done. Moving a point up or down the scale is relatively easy. To make soil more acidic, add agricultural soil sulfur, as directed on the package. Make soil more alkaline by adding agricultural lime, as directed.

Julie Bawden-Davis is a garden writer and master gardener, who since 1985 has written for publications such as Organic Gardening, The American Gardener, Wildflower, Better Homes and Gardens and The Los Angeles Times. She is the author of 10 books, including Reader’s Digest Flower Gardening, Fairy Gardening, The Strawberry Story Series, and Indoor Gardening the Organic Way, and is the founder of HealthyHouseplants.com. Her backyard is a Certified Wildlife Habitat by the National Wildlife Federation