Understanding Lime Recommendations

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Taking a soil test before planting any landscape or garden can be invaluable, if you know how to use the information you get back. The soil analysis holds lots of important information; however, the numbers and recommendations may be hard to understand or apply.

First, let me remind you that the NCDA soil lab is no longer mailing paper copies of the soil test reports. Reports are available online at: http://www.ncagr.gov/agronomi/pals/

Just type in your last name to search the database and select your name. If you soil test regularly, make sure that you select the correct report year.

On your report you will see two recommendations: a lime recommendation and a fertilizer recommendation. There will also be other numerical results under “Test Results”. These test result numbers were used to make the recommendations that you see.

Lime is a soil additive usually made by pulverizing limestone (there are other materials that can be used to make lime). Lime is mainly calcium carbonate. Its main function is to decrease soil acidity (make the soil pH closer to neutral), but lime also provides some important plant nutrients. A proper pH will make essential plant nutrients available for plant uptake, ultimately leading to optimal growth and development.

For most plants, the target pH is between 6.0 and 7.0. The major exceptions are plants in the Ericaceae – blueberries, rhododendrons, and azaleas. Another exception is centipedegrass, which unlike the other major tufgrasses, needs a pH around 5.5.

Many of the soils in Lee County are naturally acidic (especially those that were forested) and a soil report will often indicate that lime needs to be applied.

There are two types of lime: calcitic and dolomitic. Calcitic lime is mainly calcium carbonate, while dolomitic lime contains both calcium and magnesium carbonates. If you have sandy soils, dolomitic lime will be the best choice because sandy soils do not hold onto calcium or magnesium well. If you have a clay soil, you will need to base your lime choice on the amount of magnesium already in the soil (if the Mg% is greater than 20, apply calcitic lime).

Lime can be applied at any time during the year, but it will take several months to fully benefit the soil. Try to apply lime before rainfall or plan to irrigate after application.

You will find both powdered and pelletized lime available. The pelletized lime is easier to use and makes less of a mess. Both may make plants look white at application, but the ghostly sheen is harmless and will disappear after water is applied.

The lime recommendation is based on the soil pH. The pH for your soil will be listed under “Test Results” if you want to get a better understanding for the recommendation.

Your recommendation will be expressed in the unit M. This unit is the same as lbs per 1000 square feet. To determine how many pounds you will need to treat the entire test area, first determine the area (length x width for a rectangle) of the region you want to apply lime to. Then divide by 1000. Take the resulting number and multiply it by the recommendation.

Only apply 50 lbs of lime per 1000 square feet at a single application. If your recommendation is higher than 50, apply the initial 50 lbs. Then, apply the remainder six months later.

Lime is an important soil additive because it can have so many positive benefits for plants. Only apply lime as recommended on your soil test. For more information on lime and its application, reference NCDA Note 4: Fertilization of Lawns, Gardens, and Ornamentals or contact our Center at 919-775-5624.