Issue 12, July 16, 2012
The Drought of 2012--How Should I Water my Lawn?
Is my lawn dead? I hear that question every year, but particularly this summer. The good news is that turfgrasses have an excellent dormancy mechanism that allows them to tolerate most droughts. The bad news is that there is no way to visually tell whether grass is dead or just dormant. So, when someone tells you your turf is dormant they're probably correct but it could also be dead; you can't tell by looking. 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. Why does this occur?
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. If you suspect this is the case, then irrigation will be necessary to survive drought.
As good as the grasses are in surviving drought, even dormant turfs require some water. Dormant turfs survive because their need for water is reduced to a small fraction of a green, growing turf, and because they have a few deep roots that can continue to extract small amounts of water. 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 six weeks, it is wise to lightly irrigate your turf with approximately ¼" of water every 2 weeks. This will provide enough water to keep your lawn alive, but not bring it out of dormancy. It is important not to water enough to bring 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.
A phrase I hear with frequency is that "brown is the new green." As a turf specialist, I don't necessarily agree with that view, but turfgrasses have evolved to tolerate summer droughts and can do so quite well. Dormancy is a water-saving feature of turfgrasses, 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/early fall. The summer of 2012 is shaping up to be one of those rare summers, think 1988, where a little irrigation may be required for survival. And while you're at it, you'll want to irrigate trees, shrubs, and groundcovers as well since the drought is stressing even trees with deep roots. (Bruce Branham, Turfgrass Specialist, University of Illinois)