Garden Guide

Understanding lime recommendations
Jan. 09, 2013 @ 05:00 AM

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

The N.C. Department of Agriculture and Consumer Services’ soil lab is no longer mailing paper copies of the soil test reports. Reports are available online at: www.ncagr.gov/agronomi/pals.

People can type in their last name to search the database and select the correct report. Those who soil test regularly should make sure that they select the correct report year.

Two recommendations will appear on the report: 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.

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. For those who have sandy soils, dolomitic lime will be the best choice because sandy soils do not hold onto calcium or magnesium well. Those who have a clay soil will need to base their lime choice on the amount of magnesium already in the soil (if the Mg percentage 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.

Both powdered and pelletized lime are 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 soil pH will be listed under “Test Results” for those who want to get a better understanding for the recommendation.

Each person’s recommendation will be expressed in the unit M. This unit is the same as pounds per 1000 square feet. To determine how many pounds will be needed to treat the entire

test area, users should first determine the area (length by width for a rectangle) of the region to which they want to apply lime, then divide by 1000. They should then 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 a recommendation is higher than 50, apply the initial 50 pounds. 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 the 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.

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