For generations, farmers have added limestone or loads of marl to ‘make the land sweet and the keep the land up’. Most of us have probably heard these words from ours grandfathers, who believed that lime would make the soil tilth and easy to plow, leading to better crops. Obviously your grandfather did not know anything about soil pH so to say, but that it is essentially what determines whether your garden plants will thrive or not. This leaves us wondering, what exactly is soil pH? In a nutshell, the pH value is a measure of the acidity of the soil and is based on a set of numbers from 1 to 14, that are universally recognized. It is a measure of the concentration of hydrogen ions in the soil solution. While the number 7 is the measure of the soil that is neutral, numbers above 7 indicate an alkaline soil and numbers below 7 indicate an acid soil.Most plants grow best where the soil is slightly acidic, in the range of pH 6 to 7. While a few plants, such as azaleas, gardenias and blueberries, grow best at lower pH levels, others such as centipede turf, camellias and potatoes, grow well in a wide range of pH conditions, but seem to flourish in more acidic soils. The other reason for lowering soil pH, is its effect on the nutrient availability for plants, as soils with a pH of over 7.8, have a prevalence of iron, zinc, and phosphorus deficiencies. The high salt levels can lead to yellowing and poor growth of the plants.
The reason for high soil pH can be deemed to the arid climates, with the rainfall not leaching the calcium and other basic materials out of the soil, like the Black Belt prairie region of central Alabama . Sometimes the high pH can be the result of gardeners inadvertently adding more lime to the soil, than needed, without taking a soil test.
The first step in lowering soil pH, is to test the soil using a soil testing kit. There are two basic types of soil testing kits, available. While one is a capsule that will change the color of the soil & water mixture, that is then viewed against a color coded chart, the other is a fully reusable probe, with a simple-to-read meter at the top. The next step includes the challenging and slow process of lowering the soil pH, using organic or inorganic soil amendments. Based on the pH, lime content, soil texture, and mineral and nutrient content, you can use any of the following methods to lower the soil pH.
In the majority of the cases, soil pH can be lowered, simply by using fertilizers containing ammonium, like ammonium sulfate and sulfur coated urea.
You can also amend the soil by adding sulfur, that is available in the two forms of dusting sulfur and aluminum sulfate. While dusting sulfur might take several months to correct the soil pH, aluminum sulfate has a more immediate effect. A costlier but effective way to lower soil pH, is by using iron sulfate. While adding sulfur is mixed with the soil, it is important that the soil is moist, aerated and warm, to enable the rapid growth of bacteria.
For those who prefer the more organic method, compost acts as a buffer to protect plants from unbalanced soil pH. You can use decayed vegetable matter, compost, stable manure and straw, etc. to increase the acidity of the soil. This method allows the pH to be slowly lowered over time, while increasing microbial life and improving the structure of your soil.It is important that before acidifying the soil, a gardener ascertains the reason as to why pH levels are high and the soil’s type. So, sandy soil would require less amendment than clay soil. Ensure that while applying the soil amendments, the correct amount of the product is added. Soils that are over acidified should be limed, to neutralize soil pH to the desired soil pH level. Once the soil pH has been acidified to the desired level, it has to be monitored over time with regular sampling and soil analysis.