Many Connecticut residents spread limestone on their garden beds and lawn as an annual ritual. Why do we do this? Some do it because their parents did it, or the guy at the garden center told them to and sold them the limestone. How much should be purchased and applied is another mystery to most. The real answers of limestone’s why, how much and when lies in the science of soil.
Soil is made up of sand, silt, and clay. The percentage of each of these three determine the soil’s texture, which will determine how the water will move through it, or hold on to moisture. More clay equals wetter soils; more sand, better drainage. The sand, silt and clay are tiny pieces of rock, broken off of bigger pieces over much time by weathering. The rocks that makes up much of Connecticut has a naturally low pH in the 4.5 to 5.5 range. Other areas of the country and world have different rocks with different pH ranges. Acid rain falling onto the ground lowers pH levels, as does the action of organic matter decomposing which produces organic acids. Even the normal function of respiration by plants mixing oxygen and water together produces carbonic acid in the soil. More acid equals lower pH. No wonder why we need to test, monitor and fight the natural tendency of our soil to stay in a low pH range.
Most plants we want to grow require a pH range of 6 to 7. This means we have to change the pH to grow plants like grass, tomatoes, peppers, squash or garlic by adding limestone which raises the pH level. The only plants consistently happy with our native range are native plants! They have evolved in the local soil. This is why blueberries, oak trees and mountain laurel fill our forests and wild areas. Pines are another tree preferring our lower pH.
Why do the grass and vegetables prefer the 6 to 7 pH range? Because more of the nutrients that these species of plants need are available when the soil pH is in that range. The easiest way to think of pH is it is a measurement of the amount of hydrogen ions in the soil. The more hydrogen ions, the more acidic the soil is. The pH of the soil affects the availability of all plant nutrients. Just as plants have ideal moisture and light requirements, they have a preferred pH range as well.
The pH range numbers 0 to 14. The middle is neutral at 7. Pure water has a pH of 7. 0 is acid or bitter; 14 is alkaline or sweet. Old time farmers used to taste the soil to determine if it was bitter (acid, low) or sweet (high, alkaline). I am glad we have pH meters and laboratory soil testing equipment now!
0_________________________________________7_____________________________________14 Acid (Bitter) Neutral Alkaline (Sweet)
Soil pH levels also affect other life in the soil such as insects, worms, fungi and bacteria. The soil is alive with more than just plants. It is an entire ecosystem sustaining many life forms all interacting with each other. The pH level is probably the most important place to start when trying to provide the best environment for whatever plants you are growing.
Have your soil tested for pH and nutrient levels at the UConn Soil Nutrient Laboratory www.soiltest.uconn.edu. Have the $12.00 basic test for Home Grounds and Landscapers done. Forms and directions are on the website. We will be offering free pH only tests at the CT Flower Show February 23-26, 2017. A half cup of soil is needed. If you don’t have snow covering your ground now, go gather some soil now and hold it until the show. Once you know the pH of your soil, we can tell you how much limestone to apply in the spring. Fall is the best time to put down lime as it needs about six months to fully react and change the soil pH. Never put limestone down on frozen or snow-covered soil to avoid it running off to areas you didn’t intend to lime, like the storm drain. Limestone will not soak into frozen soil.