In fall, there seems to be a pick-up in rounds of golf played and necessary turf management practices deployed. Late-summer through fall is a classic time to apply rescue treatments for foliar and root feeding insects, plant replacement trees and shrubs, rogue out annuals killed by early frosts, monitor for diseases, adjust sprinkler output and overseed thin areas. Along with this activity, fall turf fertilization remains one of the critical routines.

Fertilizer strategies differ among greens, tees, fairways and roughs. While it’s often easiest to treat roughs (and maybe even fairways and tees) more as lawns, and fertilize only a few times at designated times each year, it’s often favorable to spoon-feed sand-based greens with 0.1 to 0.25 pounds of soluble nitrogen (N) per 1,000 square feet in spray solution every seven to 14 days throughout the growing season until growth stops in fall. This practice may also be common on sand-based fairways or tees. In this type of system, heavier fall fertilization is a less likely strategy, whereas it is still common in areas on native soil with more nutrient- holding capacity.

Species of turf, time of year and dosage are all important fall fertilization considerations.

Keep it simple

As with many other cultural practices, the rationale and research behind the fertilization routine are often over complicated involving timing, product selection and related protocols associated with applied nutrients – but it doesn’t have to be. Yes, it’s important to apply an appropriate amount of N at the right times of year to support growth, recovery, etc., but try not to get caught up in micronutrient deficiencies unless you have a history of problems, and certainly don’t apply phosphorous (P) or potassium (K) to provide the “appropriate ratio” of nutrients if soil test results indicate sufficient concentrations of these nutrients in soil.

Instead, apply enough N to support desirable but not excessive color, growth and recovery throughout the season (even in summer), apply a micronutrient only if you suspect a deficiency – if symptoms dissipate following the application, you solved to problem, and apply P or K only if deficient according to a soil test. Remember that turfgrasses will selectively take up the amount of each nutrient needed as long as an appropriate amount is present in soil. This is the basic ideology behind newer fertilizer application guidelines you may be interested in experimenting with such as the Minimum Levels for Sustainable Nutrition (MLSN) guidelines suggested by researchers/consultants with PACE Turf and the Asian Turfgrass Center.

Rest assured, you’ll maintain quality turf and use less fertilizer overall following this method. As an example, current recommendations from Nebraska Extension are similar to MLSN guidelines and suggest a range of 25 to 50 ppm P at a 4-inch sampling depth with the Mehlich-3 soil testing method. For K, the suggested range is 40 to 80 ppm. Sites where the level of each nutrient exceeds each range do not require supplemental P or K, and sites with less than the minimum range should receive P or K fertilizer to get within the recommended range. If your soils are within each recommended range, it’s best to maintain a sufficient supply of each nutrient by providing 1/8 to 1/4 pound of P2O5 and 3/4 to 1 pound of K2O per annual pound of N. This type of strategy eliminates unnecessary applications compared to older soil nutrient recommendations that suggest much higher concentrations of P and K are required in soils where turf is grown.

Timing

In discussions with teaching pros, no doubt you’ve heard mention of the importance of timing. Usually these chats involve their clients who can’t seem to bring the head of the club forward with the correct speed, putt with the same force uphill as downhill or want to use a baseball player’s technique to strike the ball. Timing is equally as important when fertilizing golf turf, and much of the emphasis should be placed on the turfs’ ability to absorb nutrients efficiently without other adverse effects. It’s incumbent on the superintendent to apply the essential nutrients at the proper time and amount in order to meet the needs of the course without causing damage to the environment. With this in mind, it’s important to apply N fertilizer whenever needed, and not only in fall.

The single most important reason to fertilize in fall is to bolster turf recovery from the numerous stresses of summer. Other benefits include increased winter stress tolerance, potential to expand the root system without a corresponding surge in foliar growth commonly seen in spring or early summer (that may occur at the expense of increased rooting), and reduced leaf succulence and subsequent severity of various spring or summer diseases. Slow release forms of nitrogen such as sulfur coated urea and isobutydine diurea that are activated via soil moisture are appropriate for early fall applications as well as the microbially dependent urea formaldehyde, complex methylene urea and organic sources. In late fall, soil temperatures are too cold for these sources to be of benefit; in this timeframe a shift to quickly available soluble sources such as urea, ammonium nitrate and ammonium sulfate are best. If applications of K are needed, fall may not be the best time to deploy the nutrient in cool-season grasses. Potassium fertilization might increase snow mold severity, so K should be provided earlier in the season which has the added benefit of potentially reducing anthracnose severity.

Cool-season turf

With cool-season turfs such as Kentucky bluegrass, perennial ryegrass and tall fescue, good timing signals from Mother Nature are when the heat of the summer is over, yet while nutrients are still likely to be absorbed. As such, early fall and late fall are good timing targets, acting as a one-two punch for the nutritional needs of the turf. Early fall applications stimulate both foliar growth and root growth, but less foliar growth than an equal amount of applied product would encourage in spring. Photosynthate produced in late fall are not abundantly translocated to shoots, but instead move to stolons, rhizomes and roots in large part, helping the plants gain winter hardiness and earlier spring green-up.

In general, late-season programs do not eliminate the need for spring or summer fertilization, but allow the superintendent the opportunity to use lighter rates that result in uniform shoot and root growth.

The rate or dose is also a key element in success of fall fertilization. In early fall applications, rates of 0.5 to 0.75 pounds N per 1,000 square feet encourage recovery and overall turfgrass health, while light rates in the 0.2 to 0.3 pounds N per 1,000 square feet range are best in late fall when uptake is lower. In early fall, adequate time, temperature and moisture exists to encourage breakdown and utilization of the nutrients slowly and steadily, as opposed to late fall, when the goal is to get the nutrients into the plants fast and reap the benefits quickly.

Warm-season turf

As summer gives way to fall, a traditional approach with warm-season turfs such as Bermudagrass has been to reduce the frequency and intensity of the N applications in an effort to glide into late fall or early winter without much in the way of hearty plant growth that is likely to be damaged with ensuing cold temperatures. It’s difficult to argue with this tried-and-true methodology, however, research at several land-grant universities has indicated that applications of soluble nitrogen in mid-fall produce enhanced fall and spring color of Bermudagrassturf without increasing the potential for winterkill.

In light of these discoveries, the application of low to moderate rates (0.2 to 0.4 pounds N per 1000 square feet) of quick release N approximately two weeks before the onset of dormancy will provide needed nutrients for root and rhizome growth without stimulating excessive foliar growth. The lower, more quickly available formulations are in keeping with the questioning of the eventual fate of the nitrogen previously recommended, in either the slowly or quickly available forms. The basic question is: If a large amount was applied in the fall, and a small amount was recovered in the spring, then what happened to the remainder? Really, only two possibilities exist: 1) It was used by the plant; or 2) It left the turf and moved to the atmosphere or leached to groundwater. Both are undesirable outcomes. The balance with this approach is applying just enough that will be immediately absorbed utilized in the plant, but not more than is needed, as it is likely to be wasted or lost from the site.

Trees, shrubs and other ornamentals that don’t share the same space as regularly fertilized turfgrass may require annual or seasonal fertilization.

Follow-up protocol

After late-season fertilizer applications have been made, it’s important to wash the product off the blades and into the thatch. A light irrigation is sufficient. This is recommended for two reasons. First, removing the fertilizer pellets from the leaf blades greatly reduces the chances of foliar burn, which may be more pronounced in late fall than in other times of the year. Secondly, the sooner the product can be moved into the thatch, the better. The thatch layer will act as a temporary binding agent, which will reduce the potential for off-site movement. Additionally, applications of any fertilizer product when reduced evapotranspiration in cooler months limits passive uptake via roots, or after the root zone has become frozen or a majority of the shoots have turned brown is problematic. Applications made after this point, no matter the source or composition, are likely to be lost due to leaching or surface runoff, or both.

Also fertilize trees and shrubs?

Many golf courses are comprised of a variety of plants, including trees and shrubs. Considering the content of this article, the question of whether they should be fertilized as well is natural. The answer? It depends.

A few guidelines will help determine the need for fall fertilization of most woody plants. First, are they in the midst of the turf? If they are, then they share the same root zone, and are likely to have absorbed nutrients slowly and steadily over the growing season beginning in spring as well as over the summer. Second, consider that the vast majority of trees and shrubs require about a fourth to a third of the nutrient levels that turfgrass does. If their roots are directly under the roots of the turf, it’s likely that they have already received adequate amounts for the growing season.

Another important consideration is if they show deficiency symptoms. If they have yellow leaves, yellow leaves with green veins, stunted growth, a slow-down in the rate of growth over the past few years, a thin canopy or dark blotches on stems, fruits or leaves of a color other than green, it’s possible for them to be deficient in key nutrients. Soil and tissue testing can be helpful in determining if a lack of fertility is the cause. Certain ornamentals such as azaleas, rhododendrons and holly may be problematic under alkaline soil conditions in that they require low pH levels to thrive.

Trees, shrubs and other ornamentals that are not sharing the same space as regularly fertilized turfgrass (which is generally preferred) may require annual or seasonal fertilization depending on the region of the country and species of plant. Overall, the separation of trees and turf is highly desirable as the individual needs of fertility and irrigation can be provided for both, and mower and string trimmer damage can be avoided as well.