Research suggests that grass plants are most vulnerable before they have formed three new leaves. For introduced grasses, this stage generally corresponds to the accumulation of about 500 growing degree days (GDD, base 32 degrees after March 1). For many native cool-season grasses, about 1200 GDD are required to reach the three-leaf stage.

The calendar date when these growing conditions occur varies considerably from one location to another and from year to year. Knowing how many growing degree days have accumulated provides a general rule of thumb about plant development. It is more precise and may be easier to examine the important plants in your own pasture. For tame pastures, examining crested wheatgrass or smooth bromegrass plants might begin as early as mid-April. Mid-May might be a reasonable starting date to start examining native cool-season grasses such as western wheatgrass and green needlegrass. Access to pastures planted with introduced cool-season grasses provides early season flexibility and avoids early grazing on native pastures which may compromise production later in the season.

Another grazing rule of thumb which should be remembered at turnout is “never graze the same pasture at the same time of year, two years in a row.” While many operations, of necessity, have a calving pasture which is grazed at the same time of year every year, most operations can vary where cows and calves begin grazing after calving is completed. The principle is to distribute the defoliation pressure which occurs on any desirable species to different points in the season in different years. If a pasture is grazed during the same time every year, the vigor of plant species that are most vulnerable at that season will be reduced, and they may eventually be eliminated from that pasture.

Another challenge faced at turnout is developing a strategy to make use of some less desirable plants. Cheatgrass is a notable example. It is a winter annual and makes its growth very early in the season, earlier than most other grasses. Likewise, it matures very early so that it loses nutritional value quickly. One strategy for dealing with cheatgrass is to develop a grazing schedule that provides grazing pressure on cheatgrass while it is actively growing, often in late April through mid-May, but avoids grazing native grasses when they are first emerging. In order to accomplish this, livestock that can be turned out early must be available, as well as pastures to move them to when natives begin growing. Only by observing the emergence of native plants can the negative impact of early grazing be avoided.