Summary: Put lime on lawns with acid soil is a corrective action to help neutralize lawn soil. When soil is excessive acidity it hinders the growth of grass and are subjected to more frequent attacks by fungus diseases since fungal generally grow better in an acid medium.
Question: We have heard that an application of lawn lime will help soil and grass grow plus help improve the health and soil texture of our lawn. Can you explain the benefits lawn lime and why liming the soil is a good idea. Matt, Lynchburg, Virginia
Answer: Matt, the value of lime as an aid in producing bigger crops on some soils has been recognized for many years. This is not because lime is valuable as a plant food elements, but because it neutralizes soil acidity.
A large percentage of lawns and other grass areas do not require lime, the lawn soil condition being such that nothing would be gained by liming, and some harm might even result.
When actually needed, lawn lime application may prove of great benefit to grass. Soil lime works to help correct soil acidity or sourness. It helps in making certain plant food elements available to grass, and, in addition, it is a direct source of calcium and magnesium, which grass plants need in small amounts.
Lawn lime should not be considered as a substitute for fertilizer. It does not provide those food elements that are of such vital importance to grass and which are lacking in practically all soils, namely, nitrogen, phosphorus and potassium.
For simplicity’s sake, chemists have devised a scale for designating hydrogen ion concentration or intensity of acidity. The unit of measurement is known as soil pH. The neutral point on the scale, indicated by 7 is the pH value of distilled water. Values lower than pH level 7 indicate degrees of acidity while those higher indicate degrees of alkalinity. The soil pH values represent intensity of acidity or alkalinity and not quantities of acid or alkali present.
Fortunately, lawn and turf grasses will grow over a wide range of soil acidity and alkalinity, although the moderately acid soils varying from soil pH 6.0 to 6.5 probably are best. If the acidity is more intense than pH 6, lime will be needed. Soils can be too alkaline for grass but this is rare.
Excessive acidity hinders the growth of grass. It interferes with the activity of certain bacteria which change raw plant food elements into forms usable by grass. Undue acidity, preventing decay of organic matter, may mat the turf with dead roots which will diminish the circulation of air and water in heavier soils.
A turf on an extremely acid soil may be subjected to frequent attacks by lawn fungus diseases since the causal fungi generally grow better in an acid medium.
Indications of Acid Soil
The appearance of grass as an indication of soil acidity is not to be trusted. There is some evidence of the need of lawn lime in a shallow grass root system, the appearance of certain weeds, and otherwise unaccountable lack of response to fertilizer. Several causes connected with food supply, soil texture and drainage, may produce similar appearances. The sure way to know if lime is needed is to learn the pH value with a soil test.
Putting greens and other areas that have been much stimulated by acid producing fertilizers are often very acid, especially if the soil sample has a natural tendency toward acidity.
The growth of moss may be the result of an acidic soil but is more likely to result from a deficiency in plant nutrients, poor drainage or excessive shade.
To use unneeded lime on a soil is wasteful and may be harmful. If a laboratory test of the pH value of the soil shows that lime is needed, it should be applied properly, in the best form, at the best time, and in the required amount.
When to Lime
Lawn lime is most effective when mixed with the soil to the normal depth of the grass roots. On an established lawn where only soil surface application can be made, penetration is best accomplished during periods of alternate freezing and thawing. Therefore, it is best to make application of lime in the late fall, winter, or early spring.
In case of a newly prepared seed bed, lawn lime can be raked or mixed into the upper six inches. The season is of no consequence except that application is best made several weeks or even months before seeding.
Lime may be applied after plowing under a green manure crop or a heavy stand of grass and before preparation of the seed bed. This will stimulate the bacteria that break down the organic matter and liberate plant food.
Forms of Lime
The term lime, referring strictly to calcium oxide, has been broadened to include various commercial compounds of calcium and magnesium which are commonly used to overcome soil acidity what is called “dolomite lime” or “dolomitic limestone”. In most localities the only suitable forms are ground limestone and hydrated lime.
Ground limestone is native limestone crushed to an effective degree of fineness. For overcoming soil acidity, it should contain about 50 per cent of calcium oxide and should be fine enough so that about 75 per cent will pass through a 100 mesh screen and all through a 20 mesh screen.
Agricultural lime, also known as garden lime, aglime, comes from pulverized chalk or limestone. The primary active component in this type of lime is calcium carbonate. Additional chemicals that may be included are magnesium oxide, magnesium carbonate and calcium oxide.
Hydrated lime is made by heating ground limestone to such a temperature that the carbon dioxide and water are driven off. This makes burned lime, which is very caustic. By slaking with a fine spray of water as the burned lime is forced through a blower, hydrated lime is formed. A good quality soil tests about 75 per cent calcium oxide.
Quantities of Lime
A prescription for the use of lawn lime cannot be written unless an accurate soil test is made. When the pH level and the soil type are known the proper amount of a given form of lime may be calculated.
Except in extreme cases, the quantity of lime required will vary from 50 to 100 pounds per 1000 square feet, or from one ton to two tons per acre.
In liming established turf areas, not more than 50 pounds of lime per 1,000 square feet should be used in a single application. If more is needed the application should be divided among several seasons. In preparation of a new seed bed, the entire quantity desired may be added at one time, but it should be thoroughly harrowed or raked into the upper five or six inches.
It is especially difficult to change the reaction of silt or clay that is well fortified with organic matter; hence such soils require more lime than a light, sandy soil having the same intensity of acidity.
It is far better to lime too little than too much. An overdose may upset the chemical balance of the soil, causing starvation of the grass plants and permitting certain weeds to gain control of the lawn.
Lawn lime may be broadcast by hand or, better, with a mechanical spreader such as used for lawn fertilizer. Such spreaders are available in small sizes for home use, as well as in large tractor-drawn equipment.
It is important to spread evenly since the lime will not move laterally through the ground, but only downward. On established turf areas, the lime should be washed or brushed off the grass leaves to prevent burning.
Native Limestone Country
The need of a soil for lime may depend largely upon the nature of its parent material and upon the extent of leaching of alkalies.
Atlantic Seaboard and New England States are likely to hold acidic soils because of their derivation from granites, sandstones or shales. Also, soils in New York State and northern Pennsylvania tend toward acidity, as do those of eastern Ohio.
In other parts of the country soils may be alkaline. In southern Pennsylvania there is much natural limestone. Beginning in western Ohio and extending through Indiana, Illinois, Wisconsin and into the far west, soils are generally of limestone origin.
However, it is not safe to infer the acidity or alkalinity of a soil from the fact of its location in any such division of the country. There are many modifying factors. Conditions may vary, even on adjoining properties. The maintenance program may cause an alkaline soil to become acid. Or, an alkaline condition may be maintained because of regular sprinkling with water that is strong in lime, or because of frequent topdressing with soil containing lime. A soil test is always the safe guide when it comes to lawn care.