DELAWARE NUTRIENT MANAGEMENT NOTES

"Lawn Care"

The overall goal of the Delaware Nutrient Management Act is to protect and improve water quality while maintaining profitable industries impacted by nutrient management. This Act directly affects people or companies that apply nutrients to more than 10 acres of land or manage 8 or more animal units (for further information on who is affected, see Nutrient Notes from January, 2000). However, many areas of the State consist of relatively small lawns in urban and suburban areas. The cumulative impact of nutrient applications on these areas can be very significant. This Nutrient Note is primarily for people who may not be directly affected by the Act, but whose activities can have an important impact on water quality in the state of Delaware.

WHY IS NUTRIENT MANAGEMENT ON LAWNS IMPORTANT?

· Improving the management of nutrients applied to lawns is important because properly fertilized lawns will:

- Have minimal losses of nutrients. Applying nutrients at rates higher than the plants can use may result in those nutrients being washed off the lawn, into storm sewers and, eventually, surface waters. This event is defined as non-point source pollution, and it contributes to water quality problems in many areas.

- Exhibit healthy, vigorous growth. By concentrating fertilization in the fall, you help promote root growth that improves lawn vigor.

- Require fewer pesticides. Healthy plants that have not been stressed by over fertilization are better able to resist attacks by insects and diseases.

BASICS OF LAWN FERTILIZATION

· The first step in lawn fertilization is to determine exactly what plants you are fertilizing. For example, warm and cool season grasses should be managed differently. Cool season turf grows best at about 65° F and responds well to fertilization in the early spring and fall. If you fertilize cool season turf in the late spring or summer, you promote succulent growth that cannot withstand the hot, dry summers of Delaware. In fact cool season turf usually goes dormant during the summer in Delaware. There is no need to water. When fall rains return the grass will green up and begin growing. Warm season turf grows best at about 85°F. Only two species of warm season turf grow in Delaware -zoysiagrass and bermudagrass. These grasses rarely go dormant in the summer, and respond best to late spring and summer fertilization.

· It is also important to make sure that you are not simply fertilizing weeds! There are fewer annual weeds present in the fall, thus fall is the ideal time to fertilize cool season lawns. Information to help identify grasses and weed species is available from University of Delaware Cooperative Extension, lawn care centers, and most commercial lawn care companies. Determining fertilizer needs for any type of plant growth is dependent on the quality of grass desired and the level of maintenance you intend to provide. It is also dependent on the nutrients already available in the soil. Soil samples help in determining fertilizer application rates by providing information pH and availability of primary and secondary nutrients.

· Next, determine the area to be fertilized. This area will almost certainly be very different from the total acreage of the property. For example, the drawing illustrates the procedure for calculating the area of lawn to be fertilized. The area occupied by the house and driveway (1000 sq. ft. + 450 sq. ft.) should be subtracted from the total area of the property (4356 sq. ft., or about 1/10 acre). In this example, the total area to be fertilized is only about 2/3 of the total property area (4356 sq. ft. -1450 sq. ft. = 2906 sq. ft.).

· To determine the rate, form, and timing of application, you must be familiar with fertilizer formulations. Lawn fertilizers are commonly formulated based on pounds per 1000 square feet. The quantity and type of fertilizer needed depends on the plants you have and what nutrients are already in the soil (which can be determined by soil testing). A common fertilizer mix is 12-3-6, which means that 12% of the weight is nitrogen, 3% of the weight is phosphorus (as phosphate), and 6% of the weight is potassium (as "potash"). The pounds of fertilizer to apply to each 1000 sq. ft. of lawn can be calculated by dividing the percentage of the fertilizer that is nitrogen, in this case 12%, into the recommended application rate. For example, if the recommended rate for lawn fertilization is 1 lb. of nitrogen per 1000 sq. ft., the calculation would be 1 (rate of nitrogen) divided by 0.12 (12% nitrogen in the fertilizer mix). This calculation results in an application rate of 8.3 lbs. of (12-3-6) fertilizer mix for each 1000 sq. ft. of lawn.

ADDITIONAL NOTES

· Rates of fertilizer on lawns are usually based on nitrogen. Most lawns will thrive with 2 lbs. of nitrogen per 1000 square feet per year. You can apply the 2 lbs. in the fall if the fertilizer contains at least 35% slow release nitrogen. If you use quick release (or water soluble) nitrogen apply the fertilizer in two applications of 1 lb. nitrogen each.

· It is important to remember that when you use a fertilizer mix you are adding more than just the nitrogen. If your soil test indicates that you don't need any phosphorus or potassium, try to find a mix that contains very small quantities of these nutrients. For more detailed information on fertilizer rates, consult the Cooperative Extension Publication entitled "Successful Lawn Management" available from your County Extension Office.

Prepared by Susan Barton and Dave Hansen, UD Cooperative Extension

Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. John C. Nye, Dean and Director. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.

Last Updated: Monday, 19-Mar-2007 09:37:32 EDT