Key Takeaways:

• There are several different approaches to recovering from winter injury, but none of them can be successful without suitable weather conditions.
• Soil and air temperatures are the gatekeepers for turfgrass growth. Beginning recovery efforts before sufficiently warm temperatures arrive will not yield good results.
• Sod, seed and recovery of existing turf are the primary repair methods for cool-season turf areas damaged in winter. The best strategy depends on timing, resources, extent of damage, location of damage and various other factors.
• Incorporating seed into the soil via slit seeding or aeration will improve establishment.
• Taking steps to reduce the risk of winter damage in the first place is preferable to any recovery strategy.
   

Before we get into recovery strategies, it’s worth repeating an old Benjamin Franklin quote. He famously said that “An ounce of prevention is worth a pound of cure.” The best way to recover in the spring is to prevent damage from occurring in the first place! If a course can reduce its vulnerability to winter damage, that means less turf to repair each spring. Consider the following strategies to reduce the risk of damage at your course:

• Limit cart and/or foot traffic in key areas during the winter months.
• Utilize temporary greens in the late fall through early spring.
• Prune or remove trees that heavily shade high-value playing areas.
• Improve drainage in and around low spots.
• Properly apply winter disease protection programs.
• Make late fall nitrogen applications to strengthen turf going into winter.
• Raise the putting green mowing height in fall.
  
  

All of these management techniques can translate into healthier and more robust turf that will handle the winter better and be ready to bounce back quickly when the weather improves. You will probably want to use a combination of these strategies to get the best results, especially in areas that have been problematic in the past.

Even though most superintendents that work in colder parts of the world are used to seeing winterkill, it can still be disheartening to see damaged or dead areas in the spring and once again be faced with reestablishing turf. When favorable weather conditions do return, maintenance teams spring into action and the real work begins. A quick Google search will render countless published articles and research projects that address winterkill and recovery. The common theme in all of them is that timing and methods make a difference. Let’s look at how these factors influence the success of recovery and how you can use them to get damaged turf back into good order as quickly as possible.

Timing

One of the hardest things for a superintendent to do is wait. When there is something wrong on the golf course, the DNA of the superintendent demands something be done right now to fix it. They are, by nature, problem solvers. However, if the problem is winterkill and the weather is still very cold, no amount of fixing will work well.

The cold temperatures that caused turfgrass to stop growing in the fall also dictate the speed of springtime recovery. Assuming moisture and nutrients are not limiting factors, most cool-season turfgrasses grow optimally when soil temperatures are between 50-65 F and air temperatures are between 57-75 F. (Beard 2001; Pace Turf 2023).

To use an automotive analogy, if temperatures are not in these ranges, the turf will not be firing on all cylinders. There can certainly be appreciable turf growth outside of these ranges, but vigor will be reduced the farther you move away from optimum temperatures. So, whether you're seeding, sodding or just trying to get dormant turf to begin growing again, temperature is the gatekeeper. Waiting, as hard as that may be, until weather is favorable for vigorous turfgrass growth is usually the starting point for a successful recovery. Explaining to golfers why you’re waiting is a critical part of the process.

Recovery Methods

Cool-season turfgrass recovery options generally fall into one of these categories:

• Stick with what you’ve got
• Sod
• Seed
   

Stick with what you’ve got

If the turf was damaged but not dead, sticking with what you’ve already got is advisable. It’s less expensive and requires far less effort from the maintenance team. Many courses successfully use covers to protect against winter damage. Having covers in place through the winter and early spring can also help undamaged turfgrass plants recover quicker. However, introducing covers in the spring to warm up the soil or protect the plants has had mixed results. Research has consistently shown that using covers solely to recover generally doesn’t produce substantially better results than not using covers (Frank et al., 2017). There are exceptions to this, though. The resourceful maintenance team at Wayzata Country Club in Minnesota created a greenhouse over their main putting green that dramatically improved recovery after winter damage (Cauley, 2009). However, this method would not be practical on a wider scale. As temperatures begin to warm, ensuring that the turf has adequate food and moisture will be the best strategy to jump-start growth.

Sod

If winterkill hits high-value areas like greens, approaches, fairways or tees, sodding can be the best option to quickly get these areas playable again. For this reason, it is always wise to have a sizable nursery on-site that you can use for repairs. When repairing with sod from your nursery, it is advisable to cut the sod as thick as possible. Thick-cut sod will be much less susceptible to temperature fluctuations and will require less babysitting than thin-cut sod.

Keep in mind that if you need to purchase sod, it will be the most expensive recovery option. You may also have competition for that sod if many other courses in your area were also affected by winterkill. Be sure to communicate with golfers and facility staff that sod establishment and readiness for play and cart traffic will also be highly dependent on the weather. New sod might look ready for play almost immediately, but it will require time and special care to mature. Extra fertilizer, frequent small-tine aeration events, and diligent moisture management will help sod root down into the underlying soil.

Seed

When sticking with what you’ve got or sodding are not the right call, then seeding into damaged areas is the only other option. Research conducted by the University of Minnesota, Scandinavian Turfgrass and Environment Research Foundation (STERF) and Penn State helps shed some light on when and how seed should be sown into damaged areas.

• The Minnesota research tested 21 different creeping bentgrass cultivars for germinability at different soil temperatures. They found that none of the bentgrasses germinated when soil temperatures were below 40 F at a depth of 2 inches. If the soil temperature at the 2-inch depth was 45 F, most of the cultivars germinated, albeit slowly and sparsely – i.e., 14 days to get 50% germination (Cavanaugh et al, 2019).
• STERF trials showed that Agrostis capillaris (colonial bentgrass), Poa annua and Agrostis canina (velvet bentgrass) all reached 80% germination 10-12 days after being planted and subjected to day/night temperatures of 59/41 F. Under this same temperature regime, Agrostis stolonifera (creeping bentgrass) and Festuca rubra ssp. commutata (Chewings fescue) never reached 80% germination 21 days after planting. When day/night temperatures were 77/59 F, Poa annua and the bentgrasses all reached 80% germination within seven days after planting. The fescue got there three days later (Waalen et al, 2016).
• Penn State research showed that there were significant differences between cultivars of Agrostis stolonifera when seeds were subjected to “suboptimal” air temperatures – i.e., 50 F. Sowing seed via slicing produced the best results in their trials (Carroll, 2019).
   

Research trials like these can help inform how and when to seed to get the most bang for your buck. To summarize:

• Don’t plant seed when soil and average air temperatures are below 40 F and 50 F, respectively.
• Rapid establishment will happen when soil and average air temperatures reach 50 F and 57 F, respectively.
• If seeding Agrostis stolonifera when temperatures are suboptimal, consider using cultivars like ‘Pure Select’, ‘007’, ‘A-4’, ‘Crystal BlueLinks’ or ‘Greentime’. These may germinate quicker and provide better competition against unwanted Poa annua.
• Slicing or slit seeding works great. It gets the seed into the soil and protects it from weather and animals. Seeding into aeration holes can also be more effective than simply broadcast spreading.
   

Most golf courses will end up using a combination of seed, sod and regrowth to recover from winterkill, especially if it happens over large areas. The USGA article "Bringing a Putting Green Back to Life" is a good resource for deciding which methods will work best. However, even the best recovery strategies may not produce results as quickly as desired. Weather is still the king. If it is cold, recovery will be slow or nonexistent. That’s when effective communication becomes particularly important. An often-overlooked component of a great recovery program is documentation.

During the recovery process, it can be very helpful to document your progress, or lack thereof due to cold temperatures. Take lots of pictures. Keep track of the weather, soil temperatures and what you’ve done culturally. This can help with communication to golfers and management not only during the current recovery cycle, but in years to come. It can also help refine future strategies if turf loss happens again or justify projects like drainage and tree removal that can help prevent winterkill from happening in the first place.

Spring can be an exciting time of year in the golf business. Course staff and golfers are eager to get another season started. Temperatures are warming up and the grass begins to grow. However, spring can also be a stressful time for courses trying to recover from harsh winter weather. Utilizing good cultural practices and having the patience to wait until conditions are closer to optimal is a recipe for success. It bears repeating one last time that soil and air temperatures are the driving force behind turfgrass growth. When temperatures are suboptimal, patience and plenty of communication with facility staff and golfers is essential. When the weather cooperates, spring recovery can be quick and relatively painless.

References

Beard, J. 2001. Temperature optimums and lethal thresholds. TURFAX. March/April. 9(2):4.

Carroll, D. 2019. Influence of temperature on germination of bentgrass cultivars and cultural practices on establishment of creeping bentgrass. Pennsylvania State University Masters Thesis.

Cauley, M. 2009. Winter turf damage: The green in the bubble. GCM Online. September. 

Cavanaugh, M., E. Watkins, B. Horgan, G. Heineck, S. Bauer, and A. Hollman. 2019. Germinating creeping bent in the cold. Golfdom. November 8.

Frank, K., E. Bogle, J. Bryan, and J.M. Vargas Jr. 2017. Putting green reestablishment following winterkill. International Turfgrass Society Research Journal. October 19. 13(1):250-255.

Pace Turf Information Center. 2023. Growth potential model. Paceturf.org.

Waalen, W., A. Kvalbein, T. Aamlid, and C.J. Lönnberg. 2016. Successful reestablishment of golf greens following winter damages – Final report. NIBIO Rapport. 4(46).