Fall Is the Time for Lime

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I receive many calls throughout the year from both farmers and homeowners, with concerns about the quality of their crops, gardens, and lawns. One of my first questions is usually: “when was the last time you limed?”. The answer may range from “never”, “about 10 years ago” and only rarely “last year”. When properly applied (“properly” being the caveat – applied according to a soil report recommendation), liming needs to be done every three years or so. However, the effects of liming does diminish over time, and soil will need to be re-tested and lime applied on a fairly regular basis.

Let’s start with the basics. Why is liming the soil important, and what does it do? Sometimes I hear people say: “I don’t want to use lime, I want to be organic”. Liming materials originate as ground limestone which is mined from the earth. Limestone may have different naturally occurring mineral components, such as magnesium. Basic “agricultural lime” is ground limestone classified as either “calcitic” limestone (with no magnesium) or “dolomitic limestone”, which has 6% or more magnesium. For the most part, our soils benefit from some addition of magnesium, so dolomitic is often recommended. There are other limestone products that undergo additional treatments such as high temperatures to create a more concentrated product, such as burned lime or hydrated lime. These materials can be caustic to both humans and plants, and for that reason are not generally recommended for garden or agricultural use.

In North Carolina, many of our soils are very “old”, and many of the naturally occurring minerals have been leached out over the eons. What’s left in the soil are hydrogen and aluminum cations, which makes the soil acidic (it’s not the presences of pine trees and pine straw that makes our soil acidic, as I’ve heard some people say). “Soil pH” is the measure of soil acidity. Here’s the technical definition of pH: “the negative logarithm of the hydrogen concentration, expressed on a scale from 1-14”. That means that a pH of 5 is 10 times more acidic than a pH of 6.0, and 100 times more acidic than a pH of 7 (10×10=100). “7” is a neutral pH, above 7 is base, and below 7 is acidic. Our native Sandhills soil may have a soil pH around 4 – very low. Too low for most things humans want to grow. Root and plant development are severely impacted by highly acidic soils, though different plants have varying tolerances. Blueberries, for example, like quite acidic soil: around 4.8 for rabbiteye blueberries. Most vegetables prefer 6.0-6.5, with asparagus the highest, close to 7. Centipedegrass prefers a soil pH around 5.5, while Bermudagrass, zoysiagrass, and most other turfgrasses prefer something closer to 6.0, which is the reason why centipedegrass predominates in our very acidic soils.

Proper liming is critically important for healthy plant growth. This is why, when I get calls from homeowners about their lawn, I always suggest first taking a soil sample to determine if lime is needed. Weeds, poor stands, thin turfgrass with moss – many of these problems can be attributed to low soil pH. The benefits of liming to correct low soil pH are numerous. It reduces aluminum toxicity in the plant root zone; it allows plants to better access fertilizer that is applied – at low soil pH, many essential plant nutrients are tied up and are unavailable to the plant, particularly phosphorus and potassium. In our sandy soils, potassium leaching is one of our biggest problems for all plants, and it particularly affects centipedegrass which has a high potassium requirement. Liming can reduce the leaching of potassium, extending the benefit of potassium fertilizer. Lime itself is an excellent and stable source of calcium, and potentially, magnesium (if dolomitic limestone is used). Calcium is an essential building block of plant cell walls. If growing a legume such as beans or peas, or legume cover crops such as clovers, the proper pH will enhance nodulation by the bacteria in the soil involved in nitrogen fixation.

Fall is an excellent time to soil test your lawn, garden, or farm. Lime requires several months for the reduction in acidity to take effect. Applying lime in the fall means by the time spring rolls around, your soil is in peak condition to support your lawn, flowers, or vegetables. The lab at the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) provides testing for soil samples for FREE from April 1-November 27 ($4/sample during the charge period, and the wait time is as much as 8 weeks during the winter). North Carolina is one of the few states to have this free service. The N.C. Cooperative Extension of Richmond County office can assist you with the forms, boxes, and soil probe to make your sample collection easy. Bring your samples to us, and we’ll send them to the lab free of charge. We can also assist you with understanding the results of your soil test to ensure proper execution of the report recommendations. Come see us at 123 Caroline Street to pick up your soil sample materials. Your lawn and garden will thank you for it.