Winterizer – When is Best to Apply?
Q: We were taught in my agronomy classes that it’s best to stop applying nitrogen to warm-season turf when the end of summer approaches. I have heard golf superintendents say that is not true. What is your opinion on when you should stop fertilizing?
A: When it comes to professional grass management, I rely on Dr. Clint Waltz at the University of Georgia. He says the answer is different for golf courses being managed by professionals than for homeowners.
For most golf courses and sports fields some nitrogen can be applied deeper into fall without adverse effects. Because the applications are done by professionals, spreaders are typically properly calibrated, therefore, application rates of 0.05- to 0.5 lb N / 1000 square feet are achievable. Also, the nitrogen source is commonly a soluble source so effects at low rates are closely monitored, achieving minimal growth and maximum color. The applications can be applied as either a granular or spray application. Rates below 0.25 lb N / 1000 ft2 are typically applied in a liquid solution and are done very precisely to avoid spray overlaps and skips.
Lastly, but not always practiced, these low, late-season applications are made to areas that do not have a history of disease, especially spring dead spot. Because these are facilities managed by trained professionals and they are on-site daily, boundaries can be pushed.
As for homeowners and home lawns maintained by landscape professionals, who do not have total control of a lawn, it is best to be more conservative – in an attempt to make the turfgrass sustainable. Hence discontinuing nitrogen applications in late summer or early fall is best. For the Atlanta market I’d put that date at September 1. Some years that may be too early, for some it may be spot-on.
Warm-season lawns do not absorb much nitrogen as they prepare to go dormant.
Overall, I’d say it would be alright to make the last full nitrogen application (i.e. 1 lb N / 1000 square feet) either at the end of August or first week of September.
Any later than that and you’re wasting your money.