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Key Takeaways

  • Research has shown that fans are effective for reducing soil temperatures, decreasing disease incidence, and increasing turf growth during stressful environmental conditions.
  • Fans offer the most benefit when they are closer to putting surfaces. Beyond 20 feet away, the benefits can decrease significantly.
  • Cooling greens at night may be more beneficial and practical for lowering soil temperatures and promoting growth.
  • Collecting both environmental and playability data from various green sites will help you decide where fans can be most beneficial and quantify their impact.
     

Managing putting greens, especially during the dog days of summer, often requires using all the tools in the proverbial toolbox. Fans are a potentially valuable tool for managing summer turf stress, but to maximize their effectiveness, it is important to understand the science behind their benefits.

At the most basic level, fans increase airflow, which reduces the temperature and humidity in the air above putting surfaces. They are especially beneficial for greens in low-lying areas or ones surrounded by trees and other vegetation, where natural airflow is limited. Identifying microclimates where turf struggles due to limited air movement is the first step in deciding where to put fans, but is by no means the only step. Placing fans close enough to greens to produce beneficial effects is the top priority. However, their physical presence near a green can be hard for golfers to accept. This is why building support for using fans among golfers and decision-makers is also important. Explaining both why fans are needed, and why they must be placed in specific locations, is often critical to realizing their full benefits.

Whether you are trying to figure out where to place fans or how to explain why they are worth the visual and auditory impact, it is best to let data lead the way. A good place to start is by seeing what research tells us about how heat, humidity and airflow affect turfgrass performance.

Research Perspective

When it comes to published turfgrass research, there are a limited number of studies directly involving fans. However, valuable insights can also be drawn from related research. With that in mind, we will organize the following discussion around three key challenges fans are intended to address: heat stress, disease pressure, and reduced playability.

Heat stress

Over a half century ago, pioneering research documented that airflow of 4 mph across a bentgrass putting green consistently reduced the soil temperature at a 2-inch depth by 8 to 9 degrees Fahrenheit (F) relative to ambient air temperatures, with a maximum reduction of 13 F (Duff & Beard, 1966). More recent research on fans and heat stress comes from multiple studies at Auburn University (Guertal et al., 2005; Guertal & Han, 2009). Over six years, several different studies at Auburn explored the impact of fans for cooling creeping bentgrass greens, both with and without syringing. The overall message of these studies is fans are effective at reducing soil temperature and increasing plant growth. During establishment, the 24-hour use of fans increased root length and weight, and reduced soil temperatures. Similarly, on a mature green, continuous fan use resulted in longer roots and lower soil temperatures at a half-inch depth (Figure 1). These results were achieved using non-oscillating fans, 20 inches in diameter, mounted at a height of 3 feet, and generating an average wind speed of 3.8 mph.

For turf species such as creeping bentgrass or annual bluegrass, 59 F to 75 F is the optimum range for shoot growth (DiPaola & Beard, 1992). Temperature reductions become particularly important above 86 F, where respiration outpaces photosynthesis, which causes plants to consume more carbohydrates than they produce and can lead to cell damage from an imbalance of oxygen and carbon dioxide (Huang & Gao, 2000; Liu & Huang, 2001). Simply put, temperatures exceeding 86 F push cool-season turf into survival mode, especially annual bluegrass. When it comes to thinking about whether fans might help some of your greens, the question becomes, how often do greens with reduced airflow reside within the optimum temperature range, and how often do they exceed 86 F? Tracking temperature over time offers a simple starting point for deciding if and where fans may be beneficial.

An additional heat stress consideration regarding when to use fans comes from Rutgers University. Research conducted in growth chambers found that reducing nighttime soil temperature was more effective for maintaining creeping bentgrass quality and increasing root growth than reducing daytime soil temperature (Huang, 2002; Xu et al., 2003). In other words, when temperatures exceed the optimal growing range (in this case reaching 95 F), manipulating nighttime soil temperatures may be a more achievable and impactful approach. Although fans were not used in this study (soil temperatures were cooled by circulating 64 F water around turfgrass pots), these findings reinforce an important point: Effective cooling is not exclusively about reducing peak soil temperatures; it is about preserving and promoting turfgrass growth throughout highly stressful periods.

The practical takeaways from these studies are that fans can help reduce soil temperatures, and that monitoring environmental data as well as tracking putting green growth – either below ground using a soil profiler to monitor root length or above ground through clipping collection – can provide powerful data points for assessing the impacts of high temperatures on turfgrass health and vigor. Collectively, these data points offer insights into the potential need for fans through objective comparisons of both environmental conditions and plant growth on struggling greens with restricted airflow to healthier greens with unrestricted air movement.

Disease pressure

In addition to heat, elevated humidity can foster disease development by prolonging residual moisture on leaf surfaces. This is why humidity, along with temperature, are the foundations for disease prediction models (Smith et al., 2018). Fans can reduce humidity in the air above putting surfaces and additional airflow helps shorten the duration of leaf wetness from dew or rainfall, but what effect does this have on managing disease?

“At a certain point, placing fans too far away from greens is no different than not having them at all.”

Researchers at N.C. State looked at the role fans can play in reducing brown patch on creeping bentgrass greens (Peacock & Lyford, 2022). In this study, fans were mounted 3 feet above the ground and run continuously. Measurements were collected at six distances from the fans, effectively creating a range of airflow velocities. Comparisons were made for canopy temperature, leaf wetness duration, disease incidence and turfgrass quality across these distances. In terms of plant health and disease suppression, the greatest benefits were observed between 5 and 13 feet from the fan where airflow velocities ranged from 3.6 to 6.0 mph. These distances had significantly lower brown patch incidence and higher turf quality than distances farther away. For canopy temperature, during the first year, a 10.6 F difference was observed between the closest distance from the fan of 5 feet with airflow velocity of 6 mph, and the farthest distance of 45 feet, where airflow was considered negligible. In year two of the study, starting at a distance of 21 feet from the fan, where airflow velocity was 1.6 mph, there were no significant differences in canopy temperature compared to the farthest distance of 45 feet. In other words, when it comes to reducing canopy temperature, closer to the fan is better. At a certain point, placing fans too far away from greens is no different than not having them at all. As a practical note about data collection, in this study, airflow velocities were measured at just over 1 inch above the putting surface, a reminder that understanding the impact of fans requires accurately representing the conditions experienced by putting green turf as much as possible.

This is also a good time to remember the idea of using all the tools in the toolbox. Fans are not meant to be a stand-alone silver bullet for managing heat stress or disease pressure. Getting the most out of fans means viewing them as part of a comprehensive, site-specific management strategy that is complemented by other researched-based practices. Ideally, you want to stack strategies – e.g., using improved bentgrass cultivars, deploying fans and syringing – and allow them to work in conjunction with each other. 

Playability

When it comes to putting green playability, the focus is typically on ball roll. Obviously, when heat stress or disease causes turf loss, putting green speed, smoothness and trueness are all compromised. However, fans may also improve playability by promoting firmness. Along with temperature and humidity, air movement is a critical driver of evapotranspiration (ET). Increased air movement leads to increased transpiration (Huang & Fry, 2000). The other side of that coin is, when stagnant air stifles ET, not only do plants lose their primary mechanism of aboveground cooling, the effects of reduced ET can also reverberate below ground. With less moisture evaporating from the surface and transpiring from the rootzone into the atmosphere, the net result is prolonged moisture retention which can lead to softer, more receptive putting green surfaces.

From a data collection standpoint, portable moisture meters provide a practical way to map rootzone volumetric water content (VWC) across greens, showing not only whether a green is remaining wet for extended periods and may benefit from a fan, but also where moisture variability exists within a green, to help guide precise fan placement and orientation. When paired with surface firmness measurements, a comprehensive snapshot of putting green performance both above and below ground emerges that can be especially useful when communicating with golfers and decision-makers before and after fan installation.

Ultimately, the value of fans is determined by their ability to improve playing conditions. Tracking playability metrics such as green speed, smoothness, trueness, and surface firmness along with environmental conditions and plant growth will create a more comprehensive picture of putting green microclimates, turfgrass health, and putting green performance. Collectively, this information can help superintendents understand where fans will be most beneficial, build support for investing in them, and demonstrate the return on that investment.

Practical Considerations

Research points to several important factors in successful fan use: Deciding which greens will benefit most from having them, placing them close enough to greens to have a positive impact on turf health, and running them in ways that create sustained benefits. Unfortunately, golfers do not typically like seeing fans close to greens, and they prefer not to be disturbed by the noise of them running during the day. As a result, some courses end up placing fans too far away from the greens, and superintendents may encounter pushback about running them regardless of where they are located. Fortunately, research offers key data points that superintendents can use when making their case for the benefits of fans.

In terms of where to place fans, distance from the putting surface is a critical consideration. To maximize cooling effects, closer distances are better. Beyond approximately 20 feet, the beneficial effects of fan use can decrease considerably. If golfers do not want to see a fan permanently installed close to a green, the mobile fan units available today may be a reasonable compromise. These fans can be transported into place during periods of extreme stress and then removed when the difficult weather has passed. Their fuel-powered motors are noisier than permanent fans that run on electricity, but being able to limit the visual and auditory disruption to only when it is needed most is an offsetting benefit. Not to mention, if sufficient electrical power is not already present throughout the course, the cost of running it to distant green sites may prohibit installing permanent fans. When positioning portable or permanent fans, irrigation flags can be a helpful way to visualize airflow across the entire putting surface and complement individual measurements from portable anemometers.

In terms of when and how long to run fans, research has shown the benefits of continuous use during periods of stressful weather, but a balance must be struck with what golfers are willing to tolerate and the cost of operating the fans. Keeping in mind the optimum temperature range for cool-season turfgrass growth, it’s important to use fans proactively at the onset of stressful weather. Don’t wait until the turf is stressed to turn them on because by then it may be too late to maximize their benefits. Research has also shown that nighttime soil temperature reductions can be very beneficial from a turf health perspective. If 24-hour fan use is not practical, overnight cooling offers plenty of value. Overall, newer fans are quieter than earlier models thanks to design improvements, and some even have built-in motion sensors that power them down or turn them off when golfers are present, both of which can make extended daytime use less contentious. Finally, be sure to document improvements in both environmental and playing conditions to demonstrate the value of fans to decision-makers. Installing a fan on one struggling green and showing measurable improvements will help justify investing in more fans if they are needed at other greens.

Conclusions

Getting the most out of fans requires identifying the microclimates where they are needed, placing them in locations where they will be effective, and monitoring their impact once installed. Letting data lead the way through a combination of direct, localized environmental measurements such as wind speed, temperature, relative humidity and VWC provides the foundation. Building on that with plant growth metrics such as root length and clipping volume, and then adding playability data such as green speed, smoothness, trueness and firmness delivers a comprehensive assessment to inform agronomic decision-making and communication with stakeholders when it comes to installing and using fans. Ultimately, fans should be integrated into a broader putting green stress management program that includes everything from irrigation timing to turf selection. Fans are one item in a big toolbox that superintendents have available when the growing gets tough.

References

DiPaola, J.M., & Beard, J.B. (1992). Physiological effects of temperature stress. Turfgrass, 32, 231-267.

Duff, D.T., & Beard, J.B. (1966). Effects of air movement and syringing on the microclimate of bentgrass turf 1. Agronomy Journal, 58(5), 495-497.

Guertal, E.A., & Han, D.Y. (2009). Timing of irrigation for cooling bentgrass greens with and without fans. USGA Turfgrass and Environmental Research Online, 8(17), 1-5.

Guertal, E.A., van Santen, E., & Han, D.Y. (2005). Fan and syringe application for cooling bentgrass greens. Crop Science, 45(1), 245-250.

Huang, B. (2002). Getting to the root of summer bentgrass decline. USGA Green Section Record, 40(4), 21-23.

Huang, B., & Fry, J.D. (2000). Turfgrass evapotranspiration. Journal of Crop Production, 2(2), 317-333.

Huang, B., & Gao, H. (2000). Growth and carbohydrate metabolism of creeping bentgrass cultivars in response to increasing temperatures. Crop Science, 40(4), 1115-1120.

Liu, X., & Huang, B. (2001). Seasonal changes and cultivar difference in turf quality, photosynthesis, and respiration of creeping bentgrass. HortScience, 36(6), 1131-1135.

Peacock, C.H., & Lyford, P.R. (2022). Use of fans and their effects on the turf microenvironment and disease development. International Turfgrass Society Research Journal, 14(1), 1088-1091.

Smith, D.L., Kerns, J.P., Walker, N.R., Payne, A.F., Horvath, B., Inguagiato, J.C., Kaminski, J.E., Tomaso-Peterson, M., & Koch, P.L. (2018). Development and validation of a weather-based warning system to advise fungicide applications to control dollar spot on turfgrass. PLOS One, 13(3), e0194216.

Xu, Q., Huang, B., & Wang, Z. (2003). Differential effects of lower day and night soil temperatures on shoot and root growth of creeping bentgrass. HortScience, 38(3), 449-454.