Native warm-season grasses will be fully dormant by late October and do not break dormancy again until late March in the mid-South. These dates may shift by as much as one month moving to the northern Corn Belt and two weeks in the Deep South. What can you or should you do with these dormant grasses during this period? There are several options you should consider. The simplest option is to do nothing. However, the dormant season can also be a time for stand maintenance. There are also some options for grazing currently, including taking advantage of the “stockpile” and overseeding winter annuals. Each of these options is described in further detail in the sections below.
Once native grasses have gone dormant, there is nothing that must be done to maintain a healthy, productive stand. You can simply allow the site to remain idle. However, the first step in winter care of the stand is to ensure the grasses have had some rest prior to dormancy to enable them to store the nutrients and energy they will need to overwinter. Nevertheless, the dormant period does present opportunities for improving the productivity of the stand. Because these are warm-season species, winter is a good time to address any problems with cool-season weeds, both annuals and perennials. It is also a good time to conduct prescribed burns.
During dormancy, cool-season weeds can take advantage of the lack of competition from the warm-season perennials. The better quality the native grass stand, the less of an issue these weeds will be; dense, vigorous native grass stands provide fewer opportunities for cool-season weeds to get a foothold. Regardless, these weeds can be easily controlled in warm-season grass fields during dormancy, precisely because the native grasses are dormant. Non-selective herbicides like glyphosate can be used on dormant native grasses without injury, thus allowing either grassy or broadleaf weeds to be controlled with a single application. As is the case during the growing season, broadleaf formulations can also be used during dormancy. Because control of cool-season weeds can have a substantial impact on the vigor of native grass stands, addressing them should not be overlooked.
Prescribed burns during the dormant season can benefit native grass pastures and hayfields. Burning has a number of benefits for warm-season grasses including increased growth, improved forage nutritive quality and suppression of weeds. However, timing of these fires is important. Ideally, burning native grass pastures or hayfields should be timed to coincide with the first active growth of the grasses. In the mid-South, this will occur about April 1, depending on the spring. Earlier or later burns can present some problems.
The simplest option for gaining some grazing from dormant native grass pastures is to simply graze what was already there at dormancy. The quality of such forage is always marginal and will require some protein supplement. In terms of volume of forage, that is something that can be controlled by the amount of rest the stand received during the latter part of the growing season. In a recent Tennessee study, resting stands after early August left approximately 2,000 pounds per acre (dry matter basis) of stockpiled forage. With longer rest periods, a considerable amount of biomass can accumulate such that there could be a high degree of lodging or trampling loss. Animal performance on this dormant material will not be good, but it can sustain mature animals when supplemented with protein. In fact, in much of the Great Plains, such forage is the predominant source of winter feed for many herds.
Overseeding winter annuals
Another option for more fully utilizing native grass acreage during winter months is to overseed the field with a winter annual. This is a common practice in the Deep South with bermudagrass and can provide about 60 to 70 additional days of grazing. Typically, these additional days are in late winter and early spring with only limited grazing during fall. Recent studies in the Southeast have demonstrated that overseeding winter annuals can be done with native grasses as well.
An ongoing study is evaluating overseeding rye and a rye/clover/brassica blend over three successive winters into both switchgrass and a big bluestem/indiangrass blend. Although these data are still being analyzed at the time of this writing, there are some preliminary lessons we can glean from the project at this point. First, as has been the case with the other studies on winter annuals, no negative impact on the native grasses has been observed. Secondly, as mentioned for the Alabama study, annuals here were not productive with only limited grazing provided in two of the three years. This was due to a late planting date the first year (mid-November) and an exceptionally dry fall the second year that resulted in limited stand development for the annuals. These situations both serve to underscore the risk of annuals. Planting must be timely, September in the mid-South, and rainfall adequate to ensure strong stand development. Prolonged winter cold spells can also reduce production by delaying spring growth. And winter annuals planted into an existing perennial grass sod tend to develop more slowly than those in prepared seedbeds. On the whole then, the cost of the winter annuals and risk of getting only limited grazing need to be considered before implementing such a program.
Although these studies have shown that overseeding can work, some caution should be taken in use of this tool. Recall that competition during the early growing season can be a serious challenge for native grasses. This is a time of year when native grasses are especially vulnerable to competition. In fact, a major part of why early season prescribed burns are so effective at enhancing growth of native grasses is that such burns eliminate weeds – and thatch – and thus allow much greater light levels to reach the plants. And this increased solar radiation comes at precisely the time of year they are most able to take advantage of that light. By contrast, the shade and cooler soil temperatures the winter annuals promote work in exactly the opposite direction and handicap the native grasses. Thus, they may delay dormancy break, which requires further use of root reserves, shorten the effective growing season and potentially weaken the warm-season grasses. For example, in several studies examining use of cool-season legumes in native grasses, heavy growth of the legumes during early spring had a strong negative impact on the perennial grass.
To avoid any potential problems from such spring competition, there are three simple steps that can be taken. First, consideration must be given to which winter annuals to use when overseeding native grasses. Use of annual ryegrass with native grasses is not recommended due to its later growth season and high degree of overlap with the warm-season grasses. Annual ryegrass can also be more persistent over time, is more difficult to control and, consequently, can become a serious problem. Instead, use the cereal grains such as rye, triticale or wheat. Because cereal rye has the earliest maturity of these species, it has the advantage of a shorter period when its growth overlaps that of the native grasses.
With respect to cool-season broadleaf species, some caution is also in order. Species with aggressive early spring growth such as crimson clover should be avoided. Similarly, species that have the ability to climb and overtop the native grasses such as hairy vetch should not be used. Annuals such as forage radishes or turnips will not be a problem.
The second important step in preventing problems from winter annuals is proper grazing of the overseeded species. The annual should be grazed aggressively in late spring such that the canopy is removed early enough to minimize meaningful competition with the warm-season perennials. In practice, this means the annual should be grazed out by about April 20 in the mid-South. That date should be adjusted based on your location and the conditions for any particular spring. For hay production, earlier cuttings are likewise advantageous. However, such early cutting can be a problem in terms of suitable weather for curing hay. Thus, putting the material up as haylage will likely be necessary.
Finally, to avoid any weakening of the native grass stand, do not overseed the same field year after year. Rather, rotate the planting to a different field or skip planting altogether some years. While winter annuals make excellent forage, like all annuals the grazing season is relatively short. Furthermore, like all annuals, the yearly establishment cost makes them an expensive forage production strategy over the long run. And this problem only gets worse where stand development is poor due to delayed planting, dry fall weather, extreme cold or other factors. All of these result in reduced grazing days or yields, making the cost per unit of production greater.
Winter dormancy presents several opportunities for improving native grass stands or extending the grazing season. The dormancy of the warm-season species allows for a wide range of herbicide options, including non-selective products. Prescribed fire is an excellent tool that can also contribute to reduced competition and increased grass growth. Although many producers are not concerned about production during the dormant season, there are a few options that can extend the grazing season. First, the dormant stockpile can be grazed but will require a protein supplement. Volunteer cool-season species can also provide an opportunity for some grazing during the dormant season. And finally, overseeding winter annuals is an option. However, as is often the case with annuals, they may not be particularly cost-effective. Although several studies have shown that the annuals can be successfully overseeded into dormant native grasses, getting a good stand requires timely seeding and favorable weather conditions. It is also important to recognize the cool-season species could, in some circumstances, present too much competition for the perennials during spring dormancy break.
This article was derived from Patrick Keyser’s new book, Native Grass Forages for the Eastern U.S.