Liming and Fertilizing Established Lawns
By Thomas M. Rathier
The Connecticut Agricultural Experiment Station
153 Cook Hill Rd.
Windsor, CT 06095
Telephone: (860) 683-4977 Fax: (860) 683-4987
The amount of care one gives to a lawn depends on individual tastes. One person may be satisfied with a minimal maintenance program of regular mowing and occasional irrigation, liming or fertilization, another person might prefer a high maintenance program of regular liming, frequent fertilization, regular irrigation and mowing. Still another might prefer a moderate program somewhere in between. No one program is right. It is important to know one's individual preferences and be aware of the steps to be taken to keep the lawn at that level of maintenance.
Soil Testing. The most important step to take when considering lawn care is to have the soil tested. A soil test will give information on soil texture and organic matter content. These will reflect a lawns moisture and nutrient holding capacity. The test will also provide information on the relative acidity (pH) of the soil and whether or not limestone is needed. Levels of plant nutrients are also reported along with suggestions for fertilizer additions if necessary. To have soil tested, it is important to take a sample that is representative of the lawn. With a trowel, shovel or auger, take thin slices or borings of soil from 10 to 20 places in the lawn. Sample to a depth of 3 to 5 inches and mix all the soil together in a clean pail and send or drop off about 1/2 pint of the mixture to the Experiment Station. Submit separate samples for different or problem areas.
Liming. Turfgrass grows best in a soil with a pH of 5.5-6.5 (slightly acidic). Most Connecticut soils are naturally acid and limestone is needed regularly to maintain the proper pH. If soil test results suggest the addition of limestone to raise the soil pH, the rate of application will depend on the texture of the soil. Coarse soils such as loamy sands or sandy loams usually require small amounts of limestone to reach the desired pH. Finer textured soils such as loams or silt loams require greater amounts of limestone to make the same pH change.
There are two types of limestone that can be used on lawns. Ground dolomitic limestone is a bulky product that is slow to change the soil pH but the change will be longlasting (2-3 years). It is most successfully spread with a drop type spreader. Pelleted limestone is a very fine grind of limestone that has been pelleted in water dispersable cement. As soon as it comes in contact with water, the pellet dissolves and the limestone is available to the soil. It can be spread easily with a broadcast type spreader. Because it is a finer grind 65-75% of the amount of ground limestone suggested should be used. Its effect is not as longlasting and yearly applications might be necessary. Pelleted limestone is about 3-4 times more expensive than ground limestone.
Liming should be done in either spring or fall. If large amounts (greater than 100 lbs. per 1,000 sq. ft.) are suggested, it is best to apply half in the spring and the other half in the fall. Limestone should not be applied within 2 weeks of applying a fertilizer. This avoids a chemical reaction between the two which could result in the loss of some of the fertilizer nitrogen to the atmosphere.
Fertilizing. It is important to remember that the three major nutrients that plants need are carbon, oxygen and hydrogen. Plants do not get these from fertilizers. They come from the atmosphere and water. A fertilization program will only be effective if adequate air and water can get to the shoots and roots. Of the remaining nutrients that turfgrass needs to grow, nitrogen, phosphorus and potassium are the only ones that need to be added regularly. Calcium and magnesium are provided by limestone applications and most minor elements are naturally available in our Connecticut soils.
Lawn grasses usually require nitrogen, phosphorus and potassium in an approximate ratio of 3:1:2 (N:P205:K20). Nitrogen is usually the limiting factor because it has the greatest potential for loss due to leaching. Each application should be limited to 1 lb. of actual nitrogen per 1,000 sq. ft. There are two types of nitrogen fertilizers available: water soluble types such as ammonium nitrate, ammonium phosphates, or urea; and slow release types such as methylane urea, sulfur coated urea, urea formaldehyde, IBDU, and heat treated sewage sludge. To minimize the loss of N to leaching, slow release sources should be applied. Most turf fertilizers contain one or more of the slow release types of nitrogen.
The application rates indicated on the bags of most turf fertilizers are usually designed to supply 1 lb. of nitrogen per 1,000 sq. ft. A fertilizer containing 10% nitrogen (such as 10-6-4 or 10-5-5) needs to be applied at 10 lbs. per 1,000 sq. ft. to supply 1 lb. of nitrogen. A fertilizer with 15% nitrogen is applied at 7 lbs. per 1,000 sq. ft. A fertilizer with 20% N is applied at 5 lbs. per 1,000 sq. ft.
Turf fertilizer is most effective when it's applied at times when the turf is actively growing. The best times of the year are: early spring; late spring; early summer; late summer - early fall; and late fall or dormant period (after grass has stopped growing). Most grasses are semi-dormant during hot dry periods in the middle of summer and they should not be fertilized then. During the latter part of fall it is advisable to avoid tender, new growth that would be susceptible to frost damage. Fertilization should be withheld at that time.
The frequency of fertilizer applications is determined by the level of maintenance desired. In a minimum maintenance program, one application is made each year. The best time to make the one application is in late summer. A moderate program includes 2 applications - one in late summer - early fall and another in either late fall (dormant) early spring or late spring. A high maintenance program involves 4 or 5 annual applications in early spring, late spring, early summer, late summer - early fall and late fall (dormant). With high maintenance programs, it is important to remember that, assuming adequate water is provided, the turf will grow luxuriently. In many cases, the growth rate will be so fast that the rate of plant parts such as roots and stems (not clippings) that normally die off will be increased. This will result in an accumulation of organic matter above the soil known as thatch. When the thatch layer exceeds 3/4 inch the turf could decline due to poor aeration, insufficient water penetration and diseases. A high maintenance program should include an annual dethatching such as core cultivation or aeration.
The amount of care one gives to a lawn depends on individual tastes. One person may be satisfied with a minimal maintenance program of regular mowing and occasional irrigation, liming or fertilization, another person might prefer a high maintenance program of regular liming, frequent fertilization, regular irrigation and mowing. Still another might prefer a moderate program somewhere in between. No one program is right. It is important to know one's individual preferences and be aware of the steps to be taken to keep the lawn at that level of maintenance. The frequency of fertilizer applications is determined by the level of maintenance desired.