Spring Green Up: Timing Nitrogen Applications by Temperature

“When soil temperatures consistently measure 65 degrees (F) at the 4″ depth and are trending upwards, it’s time to fertilize warm-season turf,” says Dr. Clint Waltz, UGA Turfgrass Extension Specialist.  Resisting the temptation to fertilize warm-season turf too early in the season not only conserves valuable time and resources, but encourages a healthy competitive lawn.  Spring season air temperatures often fluctuate from lows in the mid 40’s to highs in the mid 70’s, resulting in wide swings in soil temperature.  The best time to fertilize warm-season turfgrasses such as bermudagrass, zoysiagrass, St. Augustinegrass, and centipedegrass is during the active growth season spanning May through August when air temperatures reach highs in the mid 80’s to 90’s and soil temperatures remain well above 65 degrees.

In addition to optimizing time and resources, there are other compelling reasons to avoid the premature application of nitrogen on warm-season turf. Applications during cool weather may be favoring the cool-season weeds more than the semi-dormant warm-season turf.  Spring growth begins in the root system, where stored energy is expended to produce new shoots. Early applications of nitrogen may force new tender growth on warm-season grasses that is susceptible to frost damage, thus depleting valuable energy reserves early in the season.  A number of fungal diseases are also favored by the application of nitrogen during cool, damp weather.

Bottom line: keep soil temperatures in mind as you develop and initiate your fertilizer program.

Here are a few tips for developing a fertilizer program for warm season turfgrasses:

  1. Collect a soil sample to submit to your local County Extension Agent.  (Find your agent at http://extension.uga.edu/about/county/index.cfm)
  2. Download a free lawn maintenance calendar by species from www.GeorgiaTurf.com
  3. Check the latest soil temperatures by visiting the University of Georgia Environmental Monitoring Network at www.GeorgiaWeather.net.
Greg Huber
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