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Key Takeaways

  • The potential benefits of fall and winter fertilizer applications are highly variable depending on weather and location, according to research.

  • Most golf courses growing cool-season grasses will not realize benefits from late-fall and winter fertilizer applications that could not be achieved more efficiently in other ways.

  • Courses that have heavier play in fall and winter may benefit from late-season fertilizer applications because of increased turf density and root mass.

  • Quick-release sources of nitrogen are preferable for late-season applications because you want the fertilizer to be taken up quickly in case of a sudden drop in temperature and growth.
     

All golf course superintendents know the importance of proper plant nutrition throughout the year, but timing is everything when it comes to getting the desired impact. For many decades, conventional wisdom suggested that late-fall and early winter fertilizer applications to “put the course to bed” were vital and necessary for cool-season grasses. You can easily find articles or YouTube videos telling homeowners the importance of fertilizing their lawn as Thanksgiving approaches. But if the turf isn’t taking up a high percentage of the nutrients being applied, are we achieving the desired results, or just wasting time and money?

Fortunately, we now have a strong body of research that spans decades to help us understand whether superintendents should apply fertilizer in late fall and/or early winter. Like most things in turfgrass management, the short answer is “it depends.” Before diving in, it’s worth a quick mention that dormant fertilization is different from the late-fall applications discussed here. Dormant applications are intended to be available for the plant in the spring, while late-fall fertilization is meant to be used by the turf prior to dormancy. Let’s take a look at what the research tells us about the potential turf health benefits first, then look deeper at the efficiency and cost/benefit analysis of making these applications to see if they make sense for your course.

Trends

The studies on this topic have come to a variety of conclusions depending on the region and climate where the research was conducted. Superintendents have long kept meticulous records about fertilization and combining these records with research, panels and recorded surveys helps paint a complete picture.

In the mid-1900s, many researchers and turf professionals considered applications of nitrogen (N) after September to be risky. In a 1963 article, O.J. Noer – a turfgrass science pioneer and the man behind the development of Milorganite – recommended that N applications in the northern United States should cease in September or early October to allow adequate time for the grass to harden off and become dormant to avoid winter injury and disease (Noer, 1963). A decade later, researchers from Virginia Tech recommended that cool-season turfgrasses should be fertilized in the fall to improve vigor the following season, and that even bermudagrass can benefit from fall applications of N under certain conditions (Schmidt & Shoulders, 1971). In 1977, Holman Griffin, director of the southwestern region for the NGF and former USGA agronomist, wrote in a popular trade journal that “the old theory that fertilizer applications just before cold weather are detrimental to both warm- and cool-season turf is being replaced.”

We also have surveys, like one conducted in 1989 with 25 superintendents in Wisconsin, that show an average of 47% of the mean annual N budget for their courses was applied in the fall. A follow-up survey was administered in 2007 to 41 golf course superintendents with the results showing that only 26% of the mean annual N budget was applied in October and November (Bauer et al., 2012). The studies and surveys cited above demonstrate the fact that, historically, N application trends and recommendations have been inconsistent. They also show a more-recent trend of fewer course managers applying nitrogen in late fall, and that those who do are using reduced rates.

Root Health

Researchers studying the effects of late-fall N applied to bentgrass putting greens in Virginia found that in February, rooting increased by 30% in the samples that received no fertilizer or low rates. But by April, there was no apparent difference in rooting, and in June the samples that had received more fertilizer in late fall had greater root mass (Powell et al., 1967). Similar results came from studies on Kentucky bluegrass in the mid-Atlantic and in Iowa (Hanson & Juska, 1961; Moore et al., 1996). In every case, we see increased root mass at different times of the year depending on the timing of fall N applications. September and October applications in the mid-Atlantic produced greater root mass in winter. Late-fall applications in Iowa resulted in 8%-9% greater root mass in spring. In Virginia, applications from October to February resulted in increased root mass in the summer.

The conclusion to take from all this is that timing and temperature play the key role in how the plant will take up fertilizer and when it will be utilized. What time of year is increasing root growth most important to you? Superintendents should time fall applications based on when root development matters most to them. Are you trying to promote late-winter survival, spring recovery or summer stress resistance?

"The conclusion to take from all this is that timing and temperature play the key role in how the plant will take up fertilizer and when it will be utilized."

Color and Quality

Color and turf quality can be extremely subjective, and there is limited research in colder climates overall. Research in 1988 and 1993 in central Illinois provided very interesting results on color and quality response to late-fall (November) N applications (Wehner et al., 1988). Three forms of urea were applied to two varieties of Kentucky bluegrass three times per year, with a fourth application being made in either late fall or early spring. Color was rated on a scale of 1 to 9 with 1 meaning yellow turfgrass color, 7 the minimum acceptable color, and 9 meaning dark green color. Color was rated on 64 dates over three years. When the fourth application was made in the spring, it resulted in the largest number of weeks with acceptable turfgrass color ratings of any treatment (48 weeks). In comparison, when the fourth N application was made in fall, treatments only had 39 weeks of acceptable color ratings. A huge key takeaway from this study is that the clipping weights mirrored the color ratings, so we’re talking about growth and density as well as color. The researchers concluded that while there is some enhanced spring color from a late-fall application, you would still need an N application in spring if May and June are meaningful months. It’s worth noting that the improved spring color from November N treatments was seen with straight urea and sulfur-coated urea, but not with IBDU (isobutylidene diurea).

This brings us right back to the discussion of individual needs. When is your primary season? When is your turf struggling? When is clipping yield down, or color off? Documenting your needs will allow you to efficiently target increased rooting along with canopy growth, turf color and quality.

Disease Management

Do fall nitrogen fertilizer applications provide any potential benefits when it comes to disease control? This is one area where the research conclusively says yes, but in a very specific circumstance (Miltner et al., 2004). Red thread (Laetisaria fuciformis) often occurs on perennial ryegrass in western Washington in late winter to early spring when N availability is low due to cool soil temperatures and the length of time since the last fertilizer application. Application of any of the four N sources used in the study in either November, December or January reduced the visible symptoms of red thread in March.

This means we finally have one specific targeted outcome that research backs as a true benefit of late-fall fertilization. The problem is, most courses are not in this specific situation. First, most courses in northern climates are not regularly battling red thread every spring. Second, cool-season turf in this part of the Pacific Northwest doesn’t truly go dormant, so it’s taking up at least some N all winter long. Third, those at risk often already have red thread covered in their spray program. With many modern fungicides labeled for a litany of turf diseases, there is a strong likelihood that products already being applied have you covered.

It's important to clarify that red thread disease management in this section pertains solely to N applications, and not other nutrients. Phosphorous and potassium have their own set of rules and research pertaining to disease management that we’ll dig into in another article.

Nitrogen Uptake Efficiency

The research on late-season N applications shows mixed results when it comes to improving turf health and quality. Why? Well, nitrogen uptake efficiency looks to be the answer. Some of the conventional wisdom surrounding the late-fall applications is that the cooler air temperatures in fall allow a greater portion of assimilated N to be used for carbohydrate accumulation and root or rhizome development instead of being partitioned into shoot growth (Lloyd et al., 2011; Bauer et al., 2012). The accumulation of reserve carbohydrates is often listed as a benefit among superintendents that apply late-fall N; however, research results are mixed on this, and increases in root mass are often attributed to experimental variables other than N applications, like temperature or grass type – and it remains unclear exactly how a plant partitions photosynthate when shoot growth slows in the fall.

"The research on late-season N applications shows mixed results when it comes to improving turf health and quality."

There has been very limited research on how efficiently turf plants take up nitrogen in colder climates during colder temperatures, but what we have shows there is extreme variability in efficiency. Results from the study conducted in Wisconsin cited above and referenced in Table 1 below, indicate that actively growing turfgrasses absorb applied N very efficiently (65% to 83%) regardless of N rate (Lloyd et al., 2011). Fertilizing when shoot growth becomes unresponsive to N applications still was relatively efficient (46% to 72%), especially at the lowest application rate. However, fertilizing when air temperatures approach freezing resulted in, generally, lower and more-variable uptake of applied N (15% to 60%).

As temperatures dip in late fall, the ability of the plant to take up applied N becomes increasingly inefficient and variable. Many of the benefits that are sometimes attributed to fall N applications – such as increased root growth – may occur without additional fertility. The researchers in Wisconsin that looked at Kentucky bluegrass, creeping bentgrass and Poa annua, suggest that although root growth may increase with cooler soil temperatures, this trend is not stimulated further through N fertilization. That finding is consistent with previous research as well (Mangiafico & Guillard, 2006; Powell et al., 1967).

Furthermore, if the plant can’t take up the N that is applied, it’s not being stored for future use or carbohydrate accumulation. Research into the leaching levels of N throughout the year further confirm this opinion. The timing of late-fall N applications when uptake efficiency is severely diminished results in a considerable percentage of soluble N being lost through leaching (Mangiafico & Guillard, 2006). If it’s not going in the plant, you’re simply flushing it away. Inefficiency in N uptake means inefficiency in the budget. Applying fertilizer that may or may not give you a desired result could ultimately just be waste of your resources. Additionally, some states have enacted “blackout” periods when N fertilizer cannot be applied in an effort to limit nutrient leaching or runoff in winter.

Resource Efficiency

In the end, all this research brings us back to the question of whether late-season N applications are worth it. In a world with unlimited money and bags of ammonium sulfate falling from the sky into your shop, why not make fall N applications if there is a potential benefit? But that isn’t the world we live in. Fertilizer and labor costs have both increased fairly dramatically over the past three decades.

With everything in golf course maintenance seemingly getting more expensive, it’s prudent to carefully assess the benefits versus the costs of all practices – including late-season fertilizer applications. If red thread is a potential issue at your course, you may already have it covered with scheduled fungicide applications. Improving spring and summer growth, color, and density could be solved by the more-efficient spring applications of N. However, many courses with cool-season grasses are seeing increased play in late fall and winter and may want to help the turf withstand this additional pressure as well as possible, so a late-fall N application could be worth the time and money in that case.

As you parse through the costs and benefits, recognize that application timing and N source play a big role in the potential benefits, or lack thereof. If you are going to make a late-season N application, you want to pick the most effective source.

N Sources

Based on the uptake efficiency challenges as colder temperatures move in, the best results for fall N applications reside with ammonium sulfate, in my opinion. We want the N released and available as quickly as possible to aim for higher uptake percentages. In spring, the benefits of a coated urea begin to outweigh the quick release of ammonium sulfate. Both polymer- and sulfur-coated urea will provide the desired result of timed release.

"Late-fall and winter fertilization isn’t inherently good or bad, it’s situational."

Conclusion

Late-fall and winter fertilization isn’t inherently good or bad, it’s situational. There are clear benefits when applied under the right conditions, particularly in climates where turf growth remains active into winter or where red thread is a concern. But applying N to turf as air temperatures approach freezing has extremely uncertain outcomes. You want to ask yourself whether late-season fertilizer applications make sense for your course, your climate and your goals. For most courses, it won’t. Early spring applications timed with rising temperatures will provide the necessary N for root and shoot health, along with helping to prevent diseases that occur in low-N conditions, and you can avoid the pitfall of wasting fertilizer if temperatures drop sooner than expected in the fall.

Continue to analyze your turf’s specific needs, your growing environments and your budget. These are constantly changing. By aligning application timing and fertilizer type with those variables, superintendents can make smarter, more-efficient decisions and avoid sending time and money down the drain.

References

Bauer, S., Lloyd, D., Horgan, B.P., & Soldat, D.J. (2012). Agronomic and physiological responses of cool-season turfgrass to fall-applied nitrogen. Crop Science, 52(1), 1-10. https://doi.org/10.2135/cropsci2011.03.0124

Hanson, A.A., & Juska, F.V. (1961). Winter root activity in Kentucky bluegrass (Poa pratensis L.). Agronomy Journal, 53, 372–374. https://doi:10.2134/agronj1961.00021962005300060005x

Lloyd, D.T., Soldat, D.J., & Stier, J.C. (2011). Low-temperature nitrogen uptake and use of three cool-season turfgrasses under controlled environments. HortScience, 46(11), 1545-1549. https://doi.org/10.21273/HORTSCI.46.11.1545

Mangiafico, S.S., & Guillard, K. (2006). Fall fertilization timing effects on nitrate leaching and turfgrass color and growth. Journal of Environmental Quality, 35(1), 163–171. https://doi.org/10.2134/jeq2005.0061

Miltner, E., Stahnke, G., Johnston, W., & Golob, C. (2004). Late fall and winter nitrogen fertilization of turfgrass in two Pacific Northwest climates. HortScience, 39(7), 1745-1749. https://doi:10.21273/HORTSCI.39.7.1745.

Moore, R.W., Christians, N.E., & Agnew, M.L. (1996). Response of three Kentucky bluegrass cultivars to sprayable nitrogen fertilizer programs. Crop Science, 36(5), 1296–1301. doi:10.2135/cropsci1996.0011183X003600050037x

Noer, O.J. (1963). Winter injury to cool season turf. Golf Course Reporter, 31, 38–40.

Powell, A.J., Blaser, R.E., & Schmidt, R.E. (1967). Effect of nitrogen on winter root growth of bentgrass. Agronomy Journal, 59(6), 529-530. https://doi:10.2134/agronj1967.00021962005900060012x

Schmidt, R.E., & Shoulders, J.E. (1971). Fertilization practices and quality turf. USGA Green Section Record, 9(6), 12-13.

Wehner, D.J., Haley, J.E., & Martin, D.L. (1988). Late fall fertilization of Kentucky bluegrass. Agronomy Journal, 80(3), 466-471.