If your soil is in the alkaline range, you might need to seek help. Alkaline, or basic, is defined as any value on the pH scale (0-14) above a neutral of 7.0. Most alkaline soils are found in the western United States, where the pH of these soils can get as high as 10.0. A soil pH above 8.5 indicates the presence of sodium in your soil. These are known as “sodic” soils and can contain so much excess sodium that these soils become impermeable to water. It is most common that you will find alkaline soils in arid or dry areas like a desert. This is why it is more common to find acidic soils in residential areas since few plants tend to thrive in the desert.
Most alkaline soils are primarily caused by a calcium carbonate rich environment. An alkaline soil can be bad for your plant because the availability of many plant nutrients like iron, zinc, copper, and manganese is reduced at high pH levels (usually exceeding 7.0). This can lead to iron deficiency in plants which causes leaves to yellow, while the veins remain green.
Dr. David Han, associate professor and extension specialist (turf) Crop, Soil, and Environmental Sciences faculty at Auburn University, explained that resolving a pH that has become too high is tricky. Dr. Han said, “If a soil is too alkaline it can be done, it’s easy to overshoot, though.” You can try adding sulfur to your soil, which will produce sulfuric acid and make the soil more acidic, however by doing this, you are gambling with overshooting and making your soil too acidic rather than a more neutral pH level. Dr. Han recommended instead that you turn toward your fertilizer to solve the problem: “The way I usually tell people to make their alkaline soil more acidic is to make sure that when they fertilize they use a fertilizer that has ammonium sulfate in it.” The ammonium sulfate will help bring the pH down in your soil gradually without the risk of overdoing it. These fertilizers may be hard to come by, though, unless you make a special order.
This is when a soil test comes in handy. A soil test will tell you your soil’s pH by measuring the concentration of hydrogen ions in the soil. By understanding what level on the scale your soil has, experts are able to recommend alternative solutions for you.