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Good lawns need adequate nutrients

May 01, 2012|By JEFF SEMLER | jsemler@umd.edu
  • Jeff Semler
Jeff Semler

My last article dealt with soil testing and how it is a good idea for more than just farmers. I have received several calls and emails regarding soil testing and fertilization. 

In order to help shed additional light on the subject, I will deal with fertilizing facts for the home lawn. Much of this information can be found in Home & Garden Memo No. HG 103, published by and available from University of Maryland Extension.

A good lawn needs adequate nutrients for good growth. Lawns need regular fertilization to keep the grass growing and weeds out. The best way to determine a fertilization program for your lawn is to take a soil test.

Choose a fertilizer with the proper ratio of nitrogen, phosphorus and potassium to correspond to the soil test results. The fertilizer label will state the percentage by weight of nitrogen, phosphorus and potassium in that order.

A 100-pound bag of 10-5-5 fertilizer contains 10 pounds of actual nitrogen (100 pounds x 10 percent nitrogen = 10 pounds), five pounds of actual phosphorus (100 pounds x 5 percent phosphorus = 5 pounds), and five pounds of actual potassium (100 pounds x 5 percent potassium = 5 pounds). The amount of nutrients in any other fertilizer can be determined in the same way.

How do you choose between products with the same nutrient content? The big choice is between fast and slow release of the nitrogen fraction. The percentage of the total nitrogen that is water insoluble and that which is water soluble usually is listed on the fertilizer bag. In the water soluble form, the nitrogen is available quickly, and in the insoluble form, it is available slowly.

A good turf fertilizer contains some of each kind of nitrogen. The slow release portion provides nitrogen over a period of time, but is not available to the plant during cool weather. The soluble fraction, or fast release, will provide nitrogen almost immediately after application and during cool weather. Something approaching 30 percent to 50 percent insoluble or slow release (time released) nitrogen is suggested.

University research has shown that fall (August or September) and late fall (October, November or December) fertilization is ideal for home lawns. Fertilization during these times will benefit lawns more than any other practice. Most homeowners place too much emphasis on spring and summer fertilization. Some fertilizer may be needed during the spring if turf is weak or thin. However, over-application of fertilizer during the spring and summer can cause disease and other problems and result in “summer lawn nightmares.”

Disease and weed problems are usually less severe when fall and late fall fertilization are practiced. Heat and drought tolerance are usually better, thus enhancing summer lawn quality. Finally, the grass plant produces more root mass and a deeper root system, resulting in an overall healthier plant.

Lime, another nutrient needed to help balance pH, should be applied only when a soil test indicates a need for it. Excessive amounts of lime in the soil might be detrimental to the production of good turf. When a soil test is made, apply the amount recommended. Liming will not reduce the need for fertilizing. The presence of moss in the lawn does not necessarily indicate a need for lime.

It is advisable to return grass clippings to the lawn because they are a valuable source of nutrients. Research has shown that when clippings are removed, a third more nitrogen fertilizer was necessary to maintain the same color and density as areas where clippings were returned.

Furthermore, and contrary to popular belief, grass clippings do not contribute to thatch accumulation if the turf is maintained at its recommended cutting height and not more than a third of the leaf surface is removed at one mowing.

I hope this will help clear up any questions I might have raised. 

For more information, call or email the Extension staff and someone will be happy to assist you.

Jeff Semler is an Extension educator, specializing in agriculture and natural resources, for the University of Maryland Extension. He is based in Washington County. He can be reached at 301-791-1404, ext. 25, or by email at jsemler@umd.edu.

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