Soil pH – a Matter of Balance

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Written by: Charlotte Glen, Horticulture Agent

Do you know the pH of your soil? There is a good chance it is either too high or too low. Soil pH problems are common in our area, often causing poor plant growth, pale or discolored leaves, and wasted fertilizer applications. Adjusting soil pH can dramatically improve plant performance, but first you need to know which direction it needs to be adjusted. Lime and sulfur, both natural products, are used to adjust soil pH.

Finding Out Your Soil pH

Soil pH is a measure of how acidic or basic a soil is and can range anywhere from 3.0 (very acidic) to over 8.0 (moderately basic) in our region. Most plants grow best when the pH is between 5.5 and 6.5. At levels higher or lower than this, several important nutrients become unavailable to plants, even if they are present in the soil. If your soil pH is too extreme, plants will not grow well, no matter how much fertilizer you add.

Soil test kits can be purchased at garden centers or online, but they do not provide accurate results or tell you how to change your soil’s pH. Fortunately in North Carolina there is an easy and free way to determine your soil pH and get recommendations for how to adjust it, through our State’s soil testing lab in Raleigh.

Operated by the NC Department of Agriculture, North Carolina’s soil testing lab is one of the largest and busiest in the country. And it’s the only one that still analyzes samples for free (for NC residents only). To send samples to the soil testing lab, bring them to your local Cooperative Extension office. For each area you would like to sample you will need at least a cup of soil. Samples can be submitted any time of the year and results are posted online, usually within three to six weeks.

Adjusting Soil pH

The ideal pH range for your soil will depend on what you are trying to grow. Most trees, shrubs, vegetables and flowers are happiest when the pH is slightly acidic, ranging between 5.5 and 6.5, but there are exceptions. Acid loving plants prefer the pH to fall from 5.0 to 5.5. Common acid lovers include azaleas, gardenias, dogwoods, camellias, centipedegrass, loropetalum, and blueberries. When the pH is too high, the new leaves of these plants appear pale or yellow and they grow poorly.

If soil test results show that your soil has a high pH, you can temporarily lower it by adding elemental sulfur, but this must be done very carefully to avoid damaging plants. To lower soil pH from 8.0 to 6.5, till two to three pounds of elemental sulfur into the soil for every 100 square feet of area before planting. It will take a couple of months of warm, wet weather for the sulfur to change the soil pH, and the effects will only last a couple of years. If your soil pH is very high, over 8.0, it is probably unrealistic to grow acid loving plants.

In very acidic soils, where the pH is below 5.0, plants will be stunted and more prone to root diseases. Nutrient disorders like blossom end rot, a common problem in tomatoes, squash, peppers, and watermelons, are also more prevalent in acidic soils. Lime is used to raise soil pH, but should only be applied if your soil test report indicates it is needed. Many factors affect the amount of lime needed to change soil pH. The only accurate way to know how much you should apply is by soil testing. Like sulfur, lime needs to be tilled into the soil to work and takes several months to change soil pH.

Learn More

Soil pH is one of several common soil problems in our area. To learn more about soil problems and how to diagnose and fix them, attend “Growing Healthy Soils”, a free class offered at the Pender Extension Office, 801 S. Walker St. in Burgaw, Saturday, April 21, from 10 a.m. to noon. Come early to shop at the Master Gardener Plant Sale, which begins at 8:30 a.m. and finishes at noon. To find out more, contact the Pender Extension Office by calling 910-259-1235.

If you have questions about gardening contact your local Cooperative Extension office: