Soil tests can help improve lawns and manage fertility in warm-season grasses
Knowing what type of grass is in your yard, coupled with the scientific results of a soil test, can help homeowners know when the best time to fertilize is and what products are best to use. While fertilizer will be needed, potassium and phosphorous may not be.
Warm-season grasses, such as Bermuda, centipede, St. Augustine and Zoysia, grow most actively during late spring to summer and are dormant in the winter. These can benefit from fertilizer nitrogen application during the active growth period.
Cool-season grasses, such as fescue and bluegrass, grow actively during the cooler time of the year and have passed the window of time to fertilize. “Fertilizing cool season grasses with nitrogen outside of the optimum time period will create stress and likely reduce stands,” said Jagathi Kamalakanthan, an agronomist with the N.C. Department of Agriculture and Consumer Services.
Kamalakanthan recommends starting with a soil test. The soil test will provide lime and fertilizer recommendations. Lime adjusts the pH level, which is critical for optimum nutrient availability. In other words, it will help fertilizer do its best work, if fertilizer is a necessary addition.
A soil pH of 6.0 is targeted for most grasses except centipede. For centipede, the soil pH should be around 5.5. If your soil pH is too low, lime can be applied to elevate it. Lime can be applied at any time. Once you make any corrections recommended by the soil test results, you do not need to apply lime for another two or three years. “You should follow a yearly fertilizer routine until you get another soil test to determine lime needs,” Kamalakanthan said.
Phosphorus and potassium levels are determined with soil testing to provide the fertilizer recommendation and a rate to best match the needs of a specific grass type. The recommended fertilizer and the rate will supply nitrogen, which stimulates growth, along with any phosphorus and potassium needed. The timing of a nitrogen application is critical for best success, Kamalakanthan said.
Nitrogen-containing fertilizer is best applied to Bermuda grass in May, July and September. Applications to St. Augustine are best targeted for May and August. When fertilizing Zoysia, May and July applications are optimum. Slow-growing centipede has much lower fertility requirements compared to all the other warm-season grasses and should receive only one nitrogen fertilizer application, either at the end of May or early June. Best success with a centipede lawn occurs when over-fertilization with nitrogen and phosphorus is avoided.
Warm-season grasses fertilized too early in the spring or too late into the fall are more susceptible to cold damage and pest issues.
“Fertilizing with the right amount of fertilizer at the right time is key to the success of your lawn,” Kamalakanthan said.
As to weed and feed fertilizers, they are abundantly available to homeowners; however, caution should be used before selecting and using them. The timing of fertilizer needs may not match best the time for herbicide application. Also, some grasses such as centipede are very susceptible to herbicide injury.
As warn-season grasses prepare for winter, it is critical to make sure that potassium is in adequate supply, especially on sandy soils. Added potassium will lessen the chance of winter kill and also help prevent some diseases. About six weeks prior to frost, consider an application of 1.5 pounds 0-0-60 per 1,000 square feet or 2 pounds 0-0-50 per 1,000 square feet. Do not apply any potassium using a fertilizer also containing nitrogen.
Soil testing is free from April 1 until about mid-November, with expected results back in about seven to 10 working days from spring through early fall.
“Now is a great time to test your soil for getting lime and fertilizer recommendations before warm-season grass begins to actively grow “Kamalakanthan said.
Information on collecting and sampling for home gardens is available at www.ncagr.gov/agronomi/pdffiles/HomeApr2014.pdf. Contact the Agronomic Services Division office at 919-733-2655 for questions regarding soil testing.