GARDENING

A nutritional plan for turf


Published: Saturday, March 2, 2013 at 6:01 a.m.
Last Modified: Thursday, February 28, 2013 at 11:45 a.m.

A few years ago, a gentleman called the Extension Service to request a season-long formula for care of his St. Augustine lawn. Although there are several factors that enter into this discussion — soil type and structure, type of grass, turf condition, traffic, weather, etc., it is possible to lay out some general guidelines, particularly for fertilizer. Remember that these may vary, depending on the above-mentioned factors.

As a starting point for any fertilizer management plan, it is important to begin with a soil test to determine the pH of the soil as well as existing nutrients. Soil test kits for sample submission to the University of Florida soils lab are available at the local extension office. The charge is very reasonable and the extension agent receives a copy of the soil test report to review it with customers, if requested.

Researchers at the University of Florida have developed some general guidelines for nutritional care of various turf varieties. These assume the grass is in good condition. Remember that the goal of any nutritional plan is to apply needed nutrients when turf is actively growing, so that as close to 100 percent of the applied material is absorbed into the plant. This will prevent loss of excess material, which is likely to leach through the soil profile and pollute the water table. As a user of fertilizer products, it is your responsibility to protect the environment by applying nutrients properly.

During a normal winter, grass is dormant in cold weather and begins to grow as temperatures, and particularly soil temperatures, start to warm. March 15 is the earliest date for fertilizer to be applied. As grass may grow for six weeks after fertilization, Oct. 1 is the last date to apply nutrients to prevent possible damage from cold weather.

A key element in turfgrass performance is nitrogen. Nitrogen contributes to the chlorophyll in plants and regulates growth and development. Methods have been developed to prolong the release of nitrogen, often called slow-release formulas. These provide nitrogen to the plant over a longer period of time and contribute to the goal of 100 percent uptake. Often fertilizers have a percentage of nitrogen that is slow-release and a percentage that is immediately available. A slow release of 50 percent or greater is preferred. A second element in turf performance is phosphorus, the second number on the fertilizer label. This element is usually abundant in Florida soils and addition of it is not recommended. The middle number of the fertilizer label, percentage of phosphorous in the bag, should be zero, unless the soil test indicates it is needed. If so, the maximum that may be applied is one-half pound in a calendar year, in two applications of one quarter pound each. Finally, potassium, expressed as the third number on the fertilizer label, is recommended in the same amount as nitrogen. Applying potassium is like giving a multi-vitamin to your grass. It reduces disease and increases drought tolerance, cold resistance and enhances root growth. Research has shown an equal ratio of nitrogen and potassium is desirable.

How much nitrogen to apply varies depending on the type of grass. For centipede and bahia, a maximum of two pounds slow-release nitrogen per 1,000 square feet annually is recommended. For St. Augustine and zoysia, a maximum of three pounds slow-release nitrogen per 1,000 square feet annually is recommended. One pound nitrogen is the maximum that may be applied at any one time, but one-half pound application each time is preferred, to maximize uptake.

In the interest of saving money on fertilizer costs, protecting water resources and maximizing turf health, overuse of fertilizer should be avoided. Developing a calendar schedule for an even application of nitrogen after March 15 and before Oct. 1, preferably at half-pound per thousand square feet at each interval, is a good way to get turf the nutrition it needs, without overfeeding.

David Holmes is Marion County extension director. Contact him at david.holmes@marioncountyfl.org.

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