Home Grown Notions: pH Level--It Matters

by Beth Cook, Mammoth Cave Transplants
What is the pH level of your soil? Did you know that the pH level greatly affects the fertility of soil and quality of plant growth? If you plan on growing a bountiful harvest of delicious vegetables, soil pH is an important factor to know; it measures the degree of acidity or alkalinity of your soil, both of which are vital to the health of your plants.

Each influences the availability of essential nutrients in the soil. To truly know your levels, a soil test is needed. Contact your county extension agent for more details. The pH scale has 14 units and is centered on 7, which is neutral. Levels below 7 are considered in the acidic range; readings above 7 are alkaline. Soil nutrients are at their optimum availability in the range between 6 and 7. Most plants grow best in this range, although some type of plant growth can take place anywhere between 3.5 and 10.

Acidic soils are common in areas with abundant rainfall, especially east of the Mississippi and the Pacific Northwest; pockets of acidic soil can occur in other places. In acidic soils, nutrients dissolve slowly or not at all. Critical plant nutrition is locked up in insoluble mineral compounds that plants cannot utilize.

Fertilizer is of little use in acidic soils because it cannot be absorbed. To correct high acidic levels in soil, add ground agricultural limestone (Lime); try to keep to manufacturer recommendations. The limestone replaces the calcium and magnesium in the soil that rain washes away; it effectively raises the pH of acidic soil.

Also try keeping the soil amended with large amounts of organic matter to help increase the soil’s buffering capacity (ability of the soil to resist a change in the pH) and the plants ability to tolerate levels of acidity. Plants grown in acidic soils have weak, shallow root systems, making it more difficult for the plants to take up the needed nutrients and water in the soil. This leads to a less vigorous plant and decreased production. Acidic soil can also cause abnormal leaf color, an increase in disease, and robust weeds that are more tolerant of acidic soils.

​One large result is tomato blossom end rot. By reducing your fertilizer, especially nitrogen, and adding lime to your garden will help. But if you add lime now to your garden in the Spring, hold off on fertilizing, to make sure and not counteract your efforts. The optimum time to add lime to your garden is in the fall. However there are several plants that may need a more acidic soil to be at their best, such as blueberries, azaleas, rhododendrons, hydrangeas, camellias, foxgloves, bleeding hearts. With these you may need to add more acid to these plants by special plant food.

As it is important for us as humans to “know our numbers” to stay healthy, it is important to know your soils numbers to keep your plants healthy.

~A gardener learns more in the mistakes than in the successes - Barbara Dodge Borland~