It’s a long time between the final days of fall and the first sweet kisses of spring sunlight, and we all need lots of sustenance to get us through the darker days of winter. That goes for turfgrass as well. Fall is the time to feed your turf so that it is ready to burst forth with new and strong growth during green-up in early spring.
Dr. Gordon Kaufmann, lead turf agronomist for Grigg and Brandt, says that fall fertilization can accelerate green-up and turfgrass vigor in the spring. In addition, selective nutrient inputs in the fall may also reduce the need for spring fertilization, particularly slow-release nitrogen sources. He advises to apply fertilizer with moderate amounts (30 to 50 percent) of soluble nitrogen and some slow-release nitrogen, ideally a 1-to-1 nitrogen-to-potassium ratio. “Low doses and frequent applications of soluble potassium will help harden off the plants for winter,” Kauffman says. “Fall is also a good time to apply any minor nutrients as determined by soil and tissue testing. Availability of minors takes time and they should be available by spring.”
Dr. Eric Miltner, agronomist, turf and ornamentals at Koch Turf and Ornamental, believes the first step for superintendents in planning fall fertilization is to be clear about their objectives. “I think of three possibilities: recovery from summer stress, especially for cool-season turf that has been through a hot summer; maintaining good playability through the fall; and conditioning turf for the upcoming stresses of winter,” he says. “You should be addressing all three of these on some level. Depending upon your location, climate, turf species and volume of play, superintendents will emphasize these objectives differently.”
As far as nitrogen application, it depends on a superintendent’s objectives and timing. For warm-season grass, some may choose not to apply any, “but if you do, the general rule of thumb is to not apply nitrogen later than one month before the average frost date for your area,” Miltner says. Too much nitrogen applied too late can leave the plant overly succulent and susceptible to cold-weather injury. “It is best to rely on low rates of readily available nitrogen for warm-season turf, or sources like polymer coated urea or methylene urea/ureaformaldehyde,” he adds. Nitrogen release from these products will slow down, and even shut down, as temperatures cool. Remaining nitrogen will carry through the winter and become available again as temperatures warm in the spring.
“For cool-season turf early in the fall, there should be some readily available nitrogen to help with recovery and promote both shoot and root growth,” Miltner says. “This could be blended with slow or controlled release nitrogen to provide extended fall nutrition. Polymer coated urea and methylene urea are great choices here. These sources will provide nitrogen early in the fall and release will slow down as temperatures cool and growth slows.” Use of polymer coated sulfur coated urea would be similar, except that release does not really shut down, so apply early enough that nutrient release is complete before winter dormancy sets in.
The proper way to fertilize in the fall ultimately depends on what type of product is being used. You want to make sure that the turf is still being fed right up to dormancy setting in. If you’re using a product with slow-release nitrogen that relies on soil microbial activity to break it down, you will need to apply it when the soil temperatures are still warm. But if you’re using a product with quick-release nitrogen, you have more flexibility in ensuring the nitrogen will get taken up by the turf.” — Chris Gray, Lebanon Turf
“Applications in early fall should contain a mix of slow- and quick-release nitrogen but then move to more quick release as the fall progresses,” says Dr. William Kreuser, assistant professor and turfgrass specialists at the University of Nebraska-Lincoln. “Current research shows that nitrogen uptake slows as evapotranspiration is reduced and temperatures cool off. Large applications of nitrogen in very late fall/early winter should be avoided. Uptake is very minimal and the nitrogen either sits in the soil or is leached out during winter precipitation/snow melt.” He adds that for highly maintained turf continue spoon-feeding nitrogen throughout the fall until growth begins to cease in late fall. This will maintain uniform color and maximize carbohydrate accumulation without overstimulating growth rate.
Pat McHugh, corporate agronomist, Southeast, for Floratine Products Group, says that fall fertilization is critical in manufacturing carbohydrate reserves to support the plants survival. The primary time for fall fertilization is when temperatures drop to a point where shoot growth is greatly reduced, but roots are still active.
“The proper way to fertilize in the fall ultimately depends on what type of product is being used,” says Chris Gray, golf industry channel manager for Lebanon Turf. “You want to make sure that the turf is still being fed right up to dormancy setting in. If you’re using a product with slow-release nitrogen that relies on soil microbial activity to break it down, you will need to apply it when the soil temperatures are still warm. But if you’re using a product with quick-release nitrogen, you have more flexibility in ensuring the nitrogen will get taken up by the turf.”
Gray says superintendents should test their course’s soil to help determine what products will provide the essential nutrients needed for reaching optimum health before entering dormancy. Turf that is fed appropriately entering the winter months almost always come out of dormancy in spring healthier and better prepared to the beginning of the growing season.
Paul Ramina, corporate agronomist, Northeast, for Floratine Products Group, says turf managers need to be aware of all weather and turf conditions and apply the products accordingly. “’For example, once hard frosts cause the leaf tissue to go dormant, nitrogen applications are not recommended because plant uptake is minimal and applied nitrogen is wasted,” he adds.
McHugh says that for bentgrass greens in the Transition Zone October – and possibly November – is the time to fall feed with granular fertilizer, usually at a 1-to-1 nitrogen-to-potassium ratio. Nitrogen release should be somewhere 60 to 70 percent slow release. “Going forward from the granular application, go to foliar-based, nutrition supplying needed micros, amino acids and carbohydrates,” McHugh says. “Use nitrogen based upon weather conditions/yield. If bentgrass goes into semi-dormancy or dormancy and then comes out of dormancy, reload the plant with minors, amino acids and carbohydrates. Repeat this every time the turf breaks dormancy and begins to metabolize, or when you need to mow.”
For ultradwarf greens, McHugh says superintendents should begin “thinking about” a last granular fertilization in August. “The decision is usually weather related and takes place likely in September. Soils are cooling off and sunlight (hours of sunlight) are rapidly shrinking.” A 1-to-1 ratio of nitrogen-to-potassium is recommended to build up a maximum amount of carbohydrates. If there is a warm winter and the ultradwarfs break dormancy, it is “very wise” to apply a foliar consisting of minors, amino acids and carbohydrates to replenish the reserves that were spent to break dormancy.
“In the Sun Belt and Florida, winter is the golf season,” McHugh says, “and the warm-season grasses do not go dormant unless located in north Florida where frost can occur.” Fertilization of warm-season turf is constant year-round. Nitrogen levels are key and should be watched very closely by the superintendent. “Other nutrients are being applied all the time in small amounts through foliar feeding. Granular nitrogen should be applied six to eight weeks, depending upon play, soils and weather. A 1-to-1 ratio of nitrogen-to-potassium still holds true in the Sun Belt areas.”
There are two factors that influence fertilizer efficacy; temperature and moisture, Gray says. “In the fall it can become difficult to accurately predict what Mother Nature provides,” Gray adds. “The warmer the temperature, the more active microbes are in the soil, which will directly affect how fast many slow-release fertilizers function.” If, for example, methylene urea is applied and the soil temperature drops, the amount of available nitrogen to the plant will be slower than expected. “That’s why quick-release fertilizers, like ammonium sulfate, may be a better product to select when the temperatures quickly drop, which does not require microbial activity to provide available nitrogen.”
Dr. Jeff Higgins, vice president of business development for Harrell’s, says tissue tests are a “great way” to monitor the success and effectiveness of a fertility program. “There is still a need for the supply of nutrients as building blocks for carbohydrates irrelevant of the tissue concentrations,” Higgins says. “It is important to pay attention to potassium levels in the tissues, however, before going into winter cold stress conditions. Ideally, these tissue concentrations should be greater than 2 percent in the tissues by weight.”
There can be some dangers in applying too much fertilizer in the fall. Dr. Raymond Snyder, director of agronomy for Harrell’s, says minimization of large soluble inputs that promote late-season succulent growth should be avoided. “Properly chose controlled-release nutrients sources are ideal for promoting the desired growth habits for turf prior to winter,” he says.
Higgins says if soluble fast-release nutrient sources are utilized, “then one needs to be careful on the total amount of nutrient applied per application, as the turfgrass plants can only absorb a certain amount of nutrient. If excessive amounts of soluble nutrients are applied, then they will be subjected to potential loss.”
Stimulating too much growth, Kreuser says, could delay dormancy, increase leaf succulence, and burn carbohydrate reserves going into winter. “Shade is also a concern in fall. The lower sun angle and shorter day length can enhance shade issues. In those situations, reducing nitrogen can be helpful. Use of a plant growth regulator will also help.”