Debra Levey Larson
University of Illinois
URBANA, ILL. —
Grasses can survive drought, but even dormant turfs require some water, according to University of Illinois researcher Bruce Branham. Branham says he’s been getting a lot of questions from people during this summer’s drought about how to tell if their lawn is dormant and can be saved.
“The good news is that turf grasses have an excellent dormancy mechanism that allows them to tolerate most droughts,” Branham said. “The bad news is that there is no way to tell visually whether grass is dormant or dead. Once rains return in the late summer, your lawn will either green up, in which case it was dormant, or it won’t green up and is dead. Usually, this isn’t an all-or-nothing event. Often portions of the lawn will green up and other parts won’t.”
Branham explained that all grasses can go dormant, but those that have damaged or compromised root systems may not be able to tolerate much moisture stress. Poor soils, insects, or diseases can result in a reduced root system and plants that can’t tolerate much drought. He said that if this is the case, irrigation will be necessary to survive drought.
“Dormant turfs survive because their need for water is reduced to a small fraction of what is needed by a green, growing turf, and because they have a few, deep roots that can continue to extract small amounts of water,” Branham said. “Once these roots have exhausted all available soil moisture, those dormant plants will die as well.
“A healthy Kentucky bluegrass lawn should be able to survive at least 6 weeks without any rainfall or irrigation. If the drought extends beyond 6 weeks, it’s wise to lightly irrigate your turf with approximately 1⁄4 inch of water every 2 weeks. This will provide enough water to keep your lawn alive but not bring it out of dormancy.”
Branham cautioned that it is important not to water so much that it brings the turf out of dormancy. “Let natural rainfall do that. You simply want to keep enough moisture in the ground that the dormant turf stays alive.”
Although some say “Brown is the new green.” Branham doesn’t agree. “It’s true that turf grasses have evolved to tolerate summer droughts and can do so quite well. Dormancy is a water-saving feature of turf grasses and in most summers, can reduce the irrigation requirement to zero. That is, a healthy lawn can get through most summers without irrigation and recover fully in the late summer to early fall. Unfortunately, the summer of 2012 is shaping up to be one of those rare summers, like 1988, where a little irrigation may be required for survival.”
Branham recommended irrigating trees, shrubs, and groundcovers as well because the drought is stressing even trees with deep roots.