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Good fertilizer programs make healthy, green lawns

Posted: January 19, 2014 - 1:04am

A good fertilizer program is necessary for a healthy and vigorous lawn. It also must be accompanied by correct mowing heights, proper irrigation schedule, and weed/pest control for the best results. A well planned fertilizer program will include the correct type and amount of fertilizer applied. During the fall, the County Extension office receives many questions on how to best prepare a lawn for the upcoming year.

The first step in establishing a quality lawn is to determine the pH and fertility of the soil. A soil test is the best way to determine these factors. The results of a soil test include recommendations for the type, the amount, and the timing of the fertilizer application. The pH of the soil is a measure of acidity, and the recommended product will be based on the desired pH for the turf growing in the soil. The product recommendation will be based on raising or lowering the acidity of the soil to suit the plant. For this discussion, Zoysia grass will be used as the turfgrass example.

The best place to start the discussion lawn preparation is with pH. The acid/base scale ranges from 0 to 14. The midpoint (7) separates acid from alkaline soils. Any number below 7 represents an acidic soil and any number above 7 represents an alkaline soil. The pH of the soil is such an important factor because nutrients become more available to the turf when the proper pH is achieved. For example, Bermudagrass grows best in soils with a pH between 5.5 and 6.5. If this pH is achieved, the fertilizer applied will be used by the turf. If this pH is not in this desirable range, the fertilizer applied will be bound to other elements in the soil and not released to the turfgrass. In other words, only 20 to 50 percent of the $25 bag of fertilizer you bought may actually be taken up by the turf.

Moving on to the fertilizer program, it is recommended that 2 to 5 pounds of nitrogen be applied to Zoysia grass each year. The recommended dates are April, June, and August. The University of Georgia does not recommend any specific fertilizer. It is important to note that with any fertilizer product it is important to follow the manufacturer’s labeled directions. My recommendations would be a fertilizer with the composition of 16-4-8 in April, 16-4-8 in June, and 5-10-15 in August. Fertilizer is labeled by its composition of Nitrogen-Phosphorus-Potassium expressed as percentages. The 16-4-8 is 16 percent Nitrogen, 4 percent Phosphorus, and 8 percent Potassium. A popular question on the topic of fertilizer is “When and how are pre-emergents applied?”

Pre-emergents come in liquid form or are included in a fertilizer. They are herbicides to control weed growth in the lawn. When pre-emergents are added to the fertilizer program for the lawn, more applications are added to the program. However, there are combination products containing fertilizers and pre-emergents that save time and money when applied to turfgrass. Spring pre-emergents give 3 to 4 months of weed control and can be applied 6 to 8 weeks apart. For example, if a fertilizer with pre-emergent is applied as recommended in April, most product labels recommend a split application 6 to 8 weeks apart at the high rate. Therefore, the desirable timetable for the split application would be in early February and another in late April. The application in February will ensure that early germinating weeds are eradicated when warmer temperatures arise in March. The fertilizer used should not have Nitrogen, which promotes growth, due to the cooler temperatures during this time of the year. The recommended fertilizer composition is a 0-0-7 with pre-emergent included for this application. The second application will be made in late April and will prevent weeds from germinating until July. The fertilizer used for this application should be high in Nitrogen to promote growth. The recommended composition for the April application would be a 20-0-8 with pre-emergent included for this application. This will condition the turf to thrive in the anticipated hot weather. These two applications will promote a weed free period from February to July. The recommendation for the June application is a fertilizer composition of 16-4-8. This will encourage health and vigor in a weed suppressed turfgrass. This application will also help replenish nutrients removed by environmental factors such as rainfall/irrigation, soil type, and grass clippings that are removed during mowing.

Fall pre-emergents give 3 to 4 months of weed control and can be applied 6 to 8 weeks apart. It is important to note that these applications use the same fertilizers used in the spring. The recommended timetable for fall fertilizer is September. However, the first fall pre-emergent application will need to be applied in early August. The reason for an August application is dictated by the earlier applications and suppression of weeds until July by the aforementioned spring timetable. This application should include a 20-0-8 fertilizer with pre-emergent. This will help eradicate late summer weeds and early winter weeds as they germinate. This will also help with replenishing nutrients removed by the same environmental factors discussed earlier. The second application would be made in late October with the 0-0-7 fertilizer with pre-emergent included. This will ensure eradication of weeds until next February. It will also ensure proper winter conditioning of the turfgrass. Then the fertilizer cycle repeats next year.

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