Extension Drought by Barton Stam

If it rains now will the grass grow?

    After a good wet year in 2011, drought has returned. I just checked my rain gauge and it looks like the spiders have moved back in. After our dry spring I’m left watching the summer afternoon clouds and hoping for some rain to fall. In early July I was at a branding near Meeteetse, and we went from 90 degrees and choking on dust to two inches of hail on the ground, soaked-to-skin and huddled around the fire for warmth. Besides the welts from the marble-sized hailstones, it felt great, but did all that moisture really do any good? I’m tempted to just say “No,” and leave it at that. Such bad news though, probably deserves a little explanation.
    Grasses in Wyoming are predominately cool season grasses, meaning they grow in the cool spring. Optimum temperatures for cool season grass growth are usually 65 to 75 degrees, with growth beginning when soil temperatures are between 40 and 45 degrees. During our hot, summer days growth comes to a stop, and many grasses enter summer dormancy until moisture and cooler temperatures return. Not all grasses are the same, and even cool season grasses grow and enter dormancy at different times. Those times vary year to year, depending on how long the soil moisture and cool temperatures remain. Last year rain and cool temperatures continued well into June, while in 2012 we warmed up and dried up early in the spring. As a result, in 2011 we had grass growth well into the summer, but this year pastures in May looked like it was August already.
    In country dominated by cool season grasses, summer rains will do little to nothing for grass growth. Some species may green up a little, but don’t count on any real forage production until the cooler temperatures of fall return, and then only if moisture also returns. When we are lucky and get the right combination of temperatures and moisture in the fall some species will readily put on growth. These conditions mirror what happens in the spring of a good year.
    In contrast, warm season grasses depend on summer rains to grow. With moisture they’ll begin to grow in 60 to 65 degree temperatures and thrive in 90 to 95 degree temperatures. A few warm season grasses are found throughout much of Wyoming, like blue grama, but they don’t usually make up a large percentage of the forage. This is because the bulk of the moisture we do get usually comes in the form of spring rains and snows. Since the moisture is here in the spring, most of our forage producing plants take advantage of this timing and grow in the cool of spring. Summer temperatures in Wyoming are usually too high for cool season grass growth, even when moisture is available.
    In short, right now it is too hot for meaningful grass growth, even if you are lucky enough to have some rain. Summer rains may help with fires, and they settle the dust for a short period, but don’t expect them to bring much relief from the forage shortage. Your ranch drought survival plan should be in full implementation. If you don’t have a survival plan, now is the time to create one. Having one on hand can help you today and also the next time drought comes calling. Contact your local UW Extension office for help with a drought survival plan.
    Barton Stam is a UW Extension educator in Sustainable Management of Rangeland Resources and can be reached at brstam@uwyo.edu.