Turfgrass management students learn early on that, despite the best agronomic management skills, they won’t be successful if they’re managing the wrong grass for the job.
Proper selection of turfgrasses for the intended use is always critical, but perhaps no more so than on an athletic field. The ideal turfgrass for an athletic field should possess the following characteristics:
- It should tolerate heavy traffic;
- It should be able to recover quickly from injury;
- It should germinate and establish rapidly from seed;
- It should have good annual color, meaning both the ability to grow at lower temperatures and also some tolerance to heat and drought.
Some other important characteristics of ideal athletic turf are that it provides stable footing for the athlete, that it’s tolerant of the mowing height upon which the sport is ideally played and has resistance to major insects and diseases. If it’s a grass for a stadium, then increased tolerance to low light conditions is crucial.
But, as we all know, there’s no such thing as the perfect grass for an athletic field.
There are several species of turfgrass and cultivars within species that can be utilized, and each has advantages and disadvantages. There is no single, clear choice.
In many cases – an athletic field is no exception – a common practice rather than establishing a monoculture (one cultivar of one species) is to establish either a blend (which is more than one cultivar of the same species) or a mix (which is more than one species of grass). Before talking about blending or mixing grasses, though, it’s important to first review the grasses commonly used for athletic field turf.
The main three species used are Kentucky bluegrass, perennial ryegrass and tall fescue. Perennial ryegrass has the best establishment vigor of any of the cool-season turfgrasses, while tall fescue ranks second-best and Kentucky bluegrass ranks last. When choosing a turfgrass, select cultivars or species that are most adapted to your unique situation – if your fields aren’t irrigated, then tall fescue may be a good choice because of its superior heat and drought tolerance. But be aware that tall fescue has lower establishment vigor compared with perennial ryegrass and less recuperative potential compared with Kentucky bluegrass.
Complicating this comparison is the continued development of dozens to hundreds of cultivars of each species. Generally speaking, while there may be considerable variation among cultivars of the same species, there aren’t – for example – tall fescue cultivars that establish more quickly than perennial ryegrass, nor that have finer texture than Kentucky bluegrass.
The Kentucky bluegrass cultivars can be subcategorized into about 10 groups based on their agronomic characteristic and genetics. Cultivars in a particular group may have characteristics that make them significantly different than other Kentucky bluegrass cultivars.
There are a few other species that should be mentioned, as they may have utility in a mix for an athletic field.
The Texas X Kentucky bluegrass hybrids have good wear tolerance and better establishment compared with Kentucky bluegrass. Some of the early cultivars had poor germination rates, and this hybrid is still being bred for improved germination vigor. But, these cultivars have a deep and extensive rhizome system, which gives them better lateral shear strength. They also have better heat and drought tolerance, which means they may be useful when establishing fields in warmer parts of the cool-season turfgrass zone.
Another hybrid being developed is transitional ryegrass, which is a cross between annual and perennial ryegrass. Transitional ryegrasses establish very quickly and germinate and establish in cool temperatures. They only last one or two seasons. But because of this, they will not over-dominate a mixture the same way that a perennial ryegrass might. The new transitional ryegrasses have moderate green color and better mowing quality compared with perennial ryegrass.
All about the blends
There are some turfgrass breeders who say cultivar development has progressed sufficiently enough that we can now, or will soon be able to, entertain the idea of planting a field that is a monoculture, which is one cultivar of a species. But the standard recommendation continues to be to a blend, or mix, of grasses with the goal of improving the overall agronomics of the field.
The benefits of blending and mixing grasses include an increased spectrum of resistance to insect and disease pests and also an improvement of the tolerance of the field to different environmental extremes. But keep in mind that mixing or blending grasses incorrectly can cause several different problems. For example, if the two species being blended have significant color or texture differences, this may be noticeable and not aesthetically pleasing. Also, if the two grasses have significant differences in growth rate, more attention to mowing may be required in order to keep the field at a uniform height of cut. Probably the biggest issue, though, occurs when grasses that are different in appearance segregate into distinct patches on the field.
Here are some possible ways that different grasses can be mixed or blended on an athletic field:
Cultivars from one species
Depending on your local climate and the sport being played, it can be appropriate to manage a field that is a blend of species. A blend of tall fescues, for example, might be appropriate for recreational soccer. Seed blends usually include two to four cultivars. If blending Kentucky bluegrass, in order to improve the genetic diversity of the stand, cultivars should be selected from more than one of the subgroups of Kentucky bluegrass. But some care needs to be taken when choosing – the aggressive cultivars may end up dominating in a blend. If the field is used for fall sports, the blend should only include cultivars with good winter characteristics so that the field maintains a uniform appearance for the whole season of play.
Kentucky bluegrass and perennial ryegrass
Kentucky bluegrass may be the grass of choice for cool-season athletic fields. But its major Achilles heel is its slow germination and long establishment time.
Perennial ryegrass has a lot of disadvantages compared with Kentucky bluegrass and because of this tends to not be seeded alone. But the significant advantage that ryegrass has is its very fast germination and establishment. Thus, the classic mix for athletic fields has been Kentucky bluegrass and perennial ryegrass. Improved perennial ryegrass cultivars have leaf color, leaf texture and growth rate that is very similar to Kentucky bluegrass and because of this they mix well together.
There are several additional advantages to mixing these grasses. The perennial ryegrass cultivars tend to be endophytic, and therefore they have resistance to certain insect pests. Also, the two grasses are, for the most part, susceptible to different diseases, which decrease the chances of a disease outbreak devastating the entire field.
Many commercial mixes of Kentucky bluegrass and perennial ryegrass are available. Ryegrass usually comprises 10 to 50 percent of the mix. As with a blend of Kentucky bluegrass, the ideal mix of bluegrass and ryegrass should include at least two cultivars. The amount of perennial ryegrass in the mix greatly influences not only the composition of the final turf stand, but also the amount of time required for grow-in before the field is ready for play.
For example, a mix that is 80 percent Kentucky bluegrass and 20 percent perennial ryegrass seeded at 2 to 3 pounds per 1,000 square feet takes about six months to be ready for play, while a mix that is 50 percent of each seeded at 3 to 5 pounds per 1,000 square feet takes about three months to be ready for play. However, a seed mix that is 50 percent bluegrass seed and 50 percent ryegrass seed won’t result in a final stand that is an even ratio of bluegrass and ryegrass. In fact, there will be far more ryegrass in the stand. The reason for this is that, even though there are far fewer ryegrass seeds (because ryegrass seeds are heavier, thus there are fewer of them per pound), ryegrass seedling survival tends to be greater.
How to decide on the ideal grass
- There is no one ideal mix of grasses that will result in the best playing surface in all locations and under all different management regimes.
- Choosing the right blend or mix of grasses for an athletic field can be as much an art as a science.
- Often, when evaluations of turfgrasses are performed, trials are conducted on individual cultivars and not on blends or mixes.
- Most of the work that has been conducted on mixes of turfgrasses was for the purpose of establishing ideal percentages of each component in the mix as opposed to comparing specific mixes with one another in a simulated athletic field environment.
- Data from the National Turfgrass Evaluation Program (NTEP) can be useful and is accessible at NTEP.org. Keep in mind, not all cultivars tested end up being released commercially. In addition, performance in these trials may not be a good indicator of the performance under wear stress, unless that was a specific component of the test.
- Also, performance in an individual test may not be a good indicator of performance in a mix with another grass. But, you can utilize this information along with publications from your state extension office and also your local seed supplier in order to determine the right blend or mix for your location, management budget and sport of play.
A general rule of thumb is that if the ryegrass component exceeds 20 percent of the mix by weight, it will dominate the final turf stand. And, since ryegrass is not as wear- or cold-tolerant as Kentucky bluegrass, this is usually not considered a good thing.
Attempts to more specifically predict final stand percentages are complicated. Some studies have recommended that a mix with 10 to 15 percent perennial ryegrass will result in a 50:50 stand. But other research has found that cultivar differences can affect this ratio. Also, over time, if the field is in the northern part of the country, the amount of perennial ryegrass in the stand may be less than a similarly established and managed field in a more moderate climate because of its lack of winter hardiness.
Another interesting consideration when mixing Kentucky bluegrass and perennial ryegrass is research that suggests certain classes of Kentucky bluegrass mix better with perennial ryegrass. Research conducted at the University of Wisconsin, for example, found that the best-quality mix was obtained when compact or aggressive Kentucky bluegrass cultivars were mixed with ryegrass. On the other hand, common Kentucky bluegrasses mixed poorly with perennial ryegrass.
Kentucky bluegrass and tall fescue
Tall fescue has traditionally been used for lower-maintenance fields where the coarser texture is not objectionable. Its advantages are its tolerance of low fertility and irrigation inputs and relatively fewer insect and disease problems. Also, tall fescue has excellent wear tolerance once established.
The idea to mix tall fescue with Kentucky bluegrass for an athletic surface became more plausible as newer tall fescue cultivars were developed. The older tall fescue varieties would segregate into distinct clumps when mixed with Kentucky bluegrass and had a far coarser leaf texture. Newer cultivars, however, are darker green, denser and have a leaf texture that’s similar to slightly coarser than Kentucky bluegrass, resulting in a better mix with Kentucky bluegrass.
Some work has been done to determine how to best mix tall fescue and Kentucky bluegrass. Tall fescue should be the dominant species in the mix (90 to 95 percent). Also, the newer cultivars respond better to lower heights of cut (1.5 to 3 inches), and it is best to maintain them closer to the lower end of their adapted mowing range to prevent them from segregating into clumps. The newer tall fescue cultivars have variable tolerance to traffic, and you should only choose those cultivars that are rated good for wear tolerance on an athletic field.
Depending on how the field is managed, the composition of the stand may gradually shift to more Kentucky bluegrass. Maintaining a lower height of cut is necessary to prevent the mix from segregating into patches. But if the mowing height is too low (below 1.5 inches) then the Kentucky bluegrass will be favored.
Repair of a tall fescue-Kentucky bluegrass field is more complicated because it’s not generally recommended to use perennial ryegrass. Perennial ryegrass may be present in some seed mixes that contain tall fescue, but the percentages are usually low – since both of these species have predominately bunch-type growth habits, they are more likely to segregate into patches.
A good strategy to maintain stand density is to heavily overseed on a yearly basis in the off-season. In-season field repair can be accomplished using either annual or transitional ryegrass. Since transitional ryegrass tends to only survive for a year or two, it’s not as likely to cause the segregation problems that overseeding with perennial ryegrass might.
Tall fescue/Kentucky bluegrass fields are becoming more popular. But even though tall fescue is a more drought- and wear-tolerant turf, remember that not all cultivars are created equally when it comes to wear tolerance. The tall fescue cultivar is resistant to brown patch, which can be a serious problem in hot weather. And, if the field is established on shallow or poor soil, the tall fescue will not be able to develop as deep a root system, which will limit its drought tolerance and require more careful attention to irrigation.