One of the first things students are taught in an introductory turfgrass management course is that there are grasses used in cooler parts of the country (northern turf, C3, or cool-season grasses) and grasses used in warmer parts of the country (southern turf, C4, or warm-season grasses). We then talk about the region of the country (often loosely defined) called the transition zone, where it’s generally too hot in the summer for cool-season grasses yet too cold in the winter for warm-season grasses. The transition zone is also where everything is tried and nothing grows particularly well.
If you manage cool-season turf in the transition zone, or even just to the north of it, then every so often in the heat of summer you’ve been in a situation where you’re trying to keep the turf alive and vigorous. During this time, you may have pondered the merits of trying bermudagrass, because it’s a warm-season species and much more tolerant of summer heat. You may also know that bermudagrass is much more capable of tolerating traffic and spreads much more rapidly than cool-season turfgrasses do. Thus, bermudagrass may seem like a logical alternative to Kentucky bluegrass, perennial ryegrass or tall fescue on an athletic field. The problem with this logic is that, in many areas where cool-season grasses are reasonably well-adapted, bermudagrass and other warm-season grasses may not be. Therefore, both management practices and expectations need to be adjusted.
In this article, we’ll focus on determining where bermudagrass can be a viable option, what to realistically expect, which cultivars of bermudagrass to try and how to manage them in the northern fringes of where bermudagrass is adapted.
A bit about bermuda
The reason warm-season grasses do so much better in hot weather is this: Plants use solar energy to combine carbon dioxide and water to form carbohydrate during photosynthesis. But as temperatures rise, the compound that attaches to carbon dioxide in the plant begins to instead attach to oxygen and this results in a wasteful process called photorespiration, which leads to carbon loss and limits growth. Warm-season plants have evolved a way to keep oxygen away from the compound that fixes carbon dioxide, which is why they can operate in higher temperatures. Thus, there’s nothing you can do with your management practices to circumvent the fact that cool-season grasses won’t perform in hot weather. In other words, you can try to minimize the effects, but you can’t prevent photorespiration.
Bermudagrass (Cynodon dactylon) is a warm-season grass that’s adapted to warm and dry climates. It’s also used (with management adjustments) in tropical climates and is adapted to grow well in temperatures between 80 and 95 degrees Fahrenheit. These characteristics make it ideally suited to withstand the heat of summer. But warm-season plants, because they evolved in warmer climates, aren’t usually capable of withstanding cold weather. Bermudagrass is no exception. It will in most cases survive as a perennial in places so long as temperatures don’t go below about 0 to minus-10 Fahrenheit. Go below those temperatures and the chance of maintaining bermudagrass without considerable loss goes down considerably. But, as field managers know, it’s not just survival we’re interested in. Once freezing temperatures occur (and usually a few weeks or so prior to that), bermudagrass will begin to go dormant and will not emerge from dormancy until soil temperatures have warmed into the 70s, which is typically the following May in the northern fringes of where it can be grown.
There has been considerable advancement in breeding of bermudagrass and some of these cultivars display improved freeze tolerance and spring green-up characteristics. Selecting one of these cultivars is critical, because our management practices won’t compensate if the bermudagrass cultivar doesn’t display adequate winter hardiness. Cultivars have been evaluated by the National Turfgrass Evaluation Program (NTEP) for this purpose. Cultivars such as Patriot, Riviera, NorthBridge and Latitude 36 appear to have traits that result in improved winter hardiness. (These are just some examples and there are many others.) New cultivars are being released all the time and you should, of course, consult with your state extension specialist for cultivar recommendations in your location.
Regardless of cultivar selected, there are two major limitations to use of bermudagrass in northern areas of the U.S. One is whether it’s warm enough in the winter in order for the majority of the stand to survive.
The other is whether it gets warm enough in the summer for the bermudagrass to thrive.
How far north?
It’s within the transition zone states that we have to be more specific about where it is that bermudagrass may be a viable option. These states form a line and include Pennsylvania, Ohio, Indiana, Illinois, Missouri and Kansas. North and west of these states, bermudagrass isn’t a good fit because it’s just too cold in the winter (temperatures can drop to the aforementioned 0 to minus-10 Fahrenheit range). South of these states, bermudagrass is pretty common because it doesn’t get too cold in the winter and it’s warm enough in the summer.
There are (somewhat approximate) maps available that show generally where bermudagrass can be grown. But when deciding if bermudagrass can be an option to try in your specific location, there are two resources that you might consider. One is the USDA Hardiness Zone Map, which divides the country into different zones based on the average annual minimum temperature. On this map, installing bermudagrass anywhere north of zone 6 (0 to minus-10 Fahrenheit) isn’t a good idea.
But it’s not just whether it gets too cold in winter – you also have to determine if you live in an area that’s warm enough in the summer to support good bermudagrass growth. There’s another resource, the American Horticultural Society Plant Heat Zone Map that divides the country into zones based on the number of days the temperature exceeds 86 degrees Fahrenheit in a typical year.
Though this is somewhat unscientific, as a rough guide, if your heat zone number plus hardiness zone number exceeds 12, then bermudagrass is probably a viable option to try. For example, bermudagrass is an option in a location like Manhattan, Kansas, where the heat zone is 7 and the hardiness zone is 6.
If your heat zone number plus hardiness zone number equals 12 (Cincinnati, Ohio: heat zone of 6 and hardiness zone of 6), then you’re on the borderline.
If it equals 11 (West Lafayette, Indiana: heat zone of 6 and hardiness zone of 5; Columbus, Ohio: heat zone of 5 and hardiness zone of 6), then you can probably – with extreme measures – make bermudagrass work for a period of time, but you’re nonetheless subject to periodic major failures.
In any location where the number is less than 11, it would be really hard to justify bermudagrass. For example, they have bermudagrass practice fields for the Cincinnati Bengals (heat zone plus hardiness zone number of 12), but they don’t for the Cleveland Browns (heat zone plus hardiness zone number of 10). The good news for areas such as Cleveland, much of Pennsylvania, northern Illinois and northern Indiana is that for the same reasons bermudagrass won’t grow well in the summer, Kentucky bluegrass and perennial ryegrass will grow just fine.
Of course, you can ignore my attempt at a somewhat more precise way of predicting if you can grow bermudagrass by simply determining if anyone around you has a field or has tried in the past. If you’re 100 miles north of any other bermudagrass (athletic turf or on a golf course), that’s a good indication that you’ll be taking your chances by trying to manage a bermudagrass field. Also, never underestimate the importance of microclimate effects. We can have good success at our research center because it’s in the middle of a large urban area. But if we were 20 miles outside of town (where it gets between five and 10 degrees colder in winter) then we might not have as good of a result.
Managing bermudagrass in the northern fringes
First and foremost, if you’re in an area where you’re taking extra measures to manage bermudagrass, it’s probably not realistic to expect that it will replace the cool-season grass on your gameday field. There is research that shows you can extend the period bermudagrass remains green in the fall through practices such as covering or even topdressing with dark-colored materials.
One problem with bermudagrass on the northern fringe of adaptation is that it will green up too late in the spring for most spring sports and goes dormant too early for fall sports. Thus, in the northern fringe of the transition zone, a more realistic use for bermudagrass might be for practice fields, thus saving wear and tear on your gameday cool-season turfgrass field. Many studies have been done at the Ohio Turfgrass Foundation Research and Education Center in Columbus, Ohio, over the years investigating how to manage bermudagrass and make it a viable alternative. But remember that Columbus, Ohio, is just a bit north of where it would normally be recommended to try bermudagrass as an athletic turf.
Irrigation should be done on an as-needed basis once the bermudagrass greens up in the spring. But this will depend in part on the characteristics of your root zone. We recommend that there be some amount of organic matter in the soil profile. When bermudagrass is grown on pure sand, a potential issue can be desiccation damage during the long dormancy period. It can be difficult to tell if bermudagrass is dormant or dead. Thus, some attention to soil moisture conditions, especially when it begins to warm but the bermudagrass is still dormant in the spring, might be necessary if growing bermudagrass on a sand-based field.
Covering the field may be one of the most important (if not labor intensive) practices that can be done to improve your chances of maintaining a viable bermudagrass field in the northern fringes. With that being said, covering the field is not only labor intensive (it can take 2.5 hours to cover a field), but you also take on the possibility of losing the staples used to keep the cover on the turf, which presents a player safety concern. On our research plots at Ohio State, when nighttime temperatures went below 55 degrees Fahrenheit (mid-September) we covered the bermudagrass at night and took the covers off in the morning after frost. The covers block a lot of light, so we uncovered during the day until the bermudagrass went completely dormant (usually the start of November) and then left the covers on until spring.
One thing to think about if considering installing a bermudagrass field is that the pest management issues (especially the selection of labelled herbicides) are different than for cool-season turfgrass. For example, while insect control may not have been as much of an issue, spring dead spot can occur. If this happens, you can put down preventative fungicides in September. But if the surface isn’t going to be used right way in the spring, you can often grow the bermudagrass out of the disease with your fertilizer applications in the spring.
Bermudagrass also uses a lot of nitrogen. During the active growing season, we typically apply 2 pounds of nitrogen per 1,000 square feet per month. These applications are typically sprayed and applied at 0.5 pounds per week on a weekly basis, using either urea or ammonium sulfate. We’ve had some success prolonging the green period in the fall by using dark-colored organic fertilizers, which might retain more heat from sunlight.
Height of cut can also influence winter hardiness of grasses. Creeping bentgrass is one of our most cold-tolerant grasses. But when managed at putting green height, there can occasionally be issues with winter survival in cold climates. This may be due either to the effect of the colder temperatures, desiccation due to drying winds, when it’s grown in a sand media or a combination of the three. But in areas where bentgrass loss occurs on a green, you don’t typically see the same loss of bentgrass managed at higher heights of cut. Similarly, we see differences in winter survival and spring recovery rates of the bermudagrass at Ohio Turfgrass Foundation Research and Education Center when managed at different heights. Thus, one strategy to aid in overwintering survival may be to maintain your bermudagrass at the highest allowable height for your sport or intended use.
Bermudagrass does have some agronomic advantages over cool-season grasses. Research and planning are two very important steps to take if contemplating trying bermudagrass. Make sure you start with a cultivar that’s most likely to be successful in your area and have a management plan, knowing that bermudagrass is managed differently than the cool-season grasses. Of course, when in doubt, you could always experiment with a small plot before committing to a whole field.