Liming Your Lawn

Liming is an important part of a turf management program in the humid, eastern United States. Rainfall exceeds 30 inches per year, leaching basic or alkaline-forming ions, such as calcium and magnesium, from the soil and resulting in an acid soil condition which restricts growth of turf. In over 24,000 lawn samples analyzed by the Virginia Tech laboratory in 1987, more than 51 percent tested less than pH 6.0. The optimum pH level for turf is in the 6.2-6.5 range. More importantly, 28 percent of the samples tested less than pH 5.5, a level at which growth of turf can be adversely affected.

However, lime should not be applied unless a soil test indicates that it's needed. Too much lime can be as harmful as too little, causing potential trace element deficiencies.

MAKING THE APPLICATION

Limestone is simple to apply. Use either a drop spreader or a spinner spreader. Uniform coverage is the key as lime is very insoluble and essentially stays where it is put. Skipped areas won't receive the lime needed to neutralize acidity. Overlapped areas, where double the recommended amount is applied, will have too high a pH level with the potential for trace element problems. To ensure even coverage, one half of the lime should be applied in one direction, and the remainder applied in a perpendicular (crisscross) pattern. If one is using ground lime, it is simple to determine if coverage is uniform because of the visible white color of the material. More care should be taken if pelletized lime is used.

If the recommendation calls for more than 50 lbs./1000 sq. ft. to established turf, the lime application should be split. For aesthetic reasons, additional applications, if required, should be applied three to six months after the first application. Applications of less than 50 lbs./1000 sq. ft. will disappear from the surface after one or two rains, while larger amounts will remain visible for a longer period of time.

BEST TIME TO APPLY

It is recommended that lime be applied in the fall to enable the material to break down over the winter for the next season's growth. However, lime can be applied any time. If a soil test in the spring indicates lime is needed, apply it at once. Lime begins to react immediately and reduces acidity and improves turf growth through the summer and fall. One word of caution - if urea fertilizer is used, apply it three weeks before the lime to permit the urea to react with the soil. If urea is applied at the same time as lime, nitrogen will be lost due to the increased pH around the fertilizer granules.

Lime is safe to use! The common forms of lime applied to turf - calcitic lime and dolomitic lime - are non-toxic to humans or grass and will not cause pollution problems.

HOW OFTEN NEEDED

An application to bring the soil pH to 6.5 should last four to six years. Soils tend to revert to their natural acidity levels, and most nitrogen fertilizers used on lawns are acid-forming, gradually decreasing the soil pH. Ammonium nitrate and urea, two commonly used nitrogen fertilizers, break down in the soil to produce nitric acid. Approximately 1 3/4 lbs. of pure lime is needed to neutralize the acidity caused by 1 lb. of nitrogen from either of these fertilizers. In a yearly fertilization program where a total of 4 lbs. of nitrogen is applied per 1000 sq. ft., approximately 7 1/4 lbs. of pure lime would be needed to neutralize the acidity the nitrogen fertilizer produces. Therefore, the soil should be tested periodically and lime applied when needed.

TYPES OF LIME

Lime materials available for purchase are calcitic lime, dolomitic lime, burned lime, hydrated lime, marl, and pelletized lime. However, not all of these are appropriate for use on established lawns.

Calcitic lime is mined from natural, limestone bedrock deposits. The soil is bulldozed off the bedrock; holes are drilled in the limestone, then it is blasted out with dynamite charges. It is crushed to about 1-inch stones, then pulverized or ground to screening specifications. Calcitic lime, also called aglime, has a neutralizing value between 85-100 percent. In addition to neutralizing soil acidity, calcitic limestone supplies calcium, an essential element for plant growth.

Dolomitic lime is mined in a manner similar to calcitic lime. It has a neutralizing value between 85-109 percent and supplies both calcium and magnesium for plant growth.

Burned lime (calcium oxide) is also called quicklime or unslaked lime and is manufactured by roasting crushed lime in a furnace to drive off carbon dioxide. It has a neutralizing value between 150-175 percent, which is the highest of all liming materials. It is a powdery, caustic material that is difficult to handle because it absorbs water very quickly. When applied, use only on the soil surface and incorporate immediately to prevent the formation of granules or flakes which decompose slowly.

Hydrated lime (calcium hydroxide), also called builder's lime or slaked lime, is manufactured by adding water to burned lime. It has a neutralizing value of between 120-135 percent. Hydrated lime is a caustic, powdery material and should not be applied to established turf since it can burn.

Marl is mined from deposits that lie below peat bogs. It is calcium carbonate material that was formed by shell deposits or produced in aquatic plants. The material, deposited along with clay and organic debris, is somewhat impure, and has a neutralizing value between 70-90 percent.

Pelletized lime is finely ground agricultural lime to which a cementing agent has been added to form "pellets." It has been in use for several years, and while it is more expensive, this material is easier to spread than regular liming materials and eliminates the dust problem commonly associated with them. The lime pellets dissolve with a soaking rain or irrigation. If pelletized lime is used for establishing new lawns, apply to the soil surface and water thoroughly before tilling. If intact pellets are incorporated, neutralization will be confined to pockets within the tilled soil since lime moves very slowly in soil.