Ronald Strahan, Koske, Thomas J.
Most conditioned, well-rooted turfgrass plants can stay in a drought-dormant state for at least three to four weeks without the grass dying. If drought goes beyond the four-week mark, it is suggested that water be applied to re-hydrate the grass and keep it alive and somewhat growing. Water enough over a day or two to wet the soil down to 5 inches. This drink will not totally green up the grass in many cases but will keep it alive. A light sprinkle at this time would especially not be good. If you catch a light rain and really need more water, this would be a great time to add to your moisture bank. Infrequent and deeper waterings prior to drought will develop deeper roots, which make plants much more sustainable.
Summer dormancy is a perfectly normal response to the stress of heat and drought. It is important to make sure grass is as healthy as possible before dormancy begins and not to stress the grass any more once conditions become unfavorable for growth. Grass should be maintained slightly higher before and during drought; extra height can mean deeper roots and cooler crowns.Grass should only be mowed as needed, and mowing should be performed early in the morning or late in the evening with a sharp blade to minimize stress on the turf. In drier conditions, grass will grow a lot less and thus require less mowing. These taller cuts also need less mowing due to the "one-third rule of cut" (never remove more than the top 1/3).
During a dormant phase caused by heat or drought, grass should not be fertilized. It's not growing due to drought, not starvation, and soil nutrients require moisture for adequate movement into the roots. Proper conditioning takes place over several weeks prior to the onset of drought. Keep nitrogen rates modest and feed almost as much potassium; this will produce healthy and tough tissues. The turf, once dormant, is not actively bringing in much soil nutrients. High fertility before or during a drought can promote injury to the grass and reduce root mass. If darker color is required, don't apply more nitrogen; consider spraying foliar iron instead.
Some weeds thrive under these reduced-water situations (like Dallis grass and Bahia grass). It is best to spot treat these areas with a weed killer or pull or cut out the weeds by hand. A broadcast application of herbicide can further stress the dormant turf. The weeds themselves, however, may also be somewhat dormant and not responsive to some herbicides.
Because the turf is dormant, it is not able to repair itself. To maintain the best lawn possible, keep heavy traffic off of the grass during dormancy. Divots and insect damage will persist until well after growth resumes.
A recent university drought study in San Antonio Texas supports these recommendations. Bermudas, St. Augustine and zoysias were examined for their ability to survive a 60-day midsummer period of no rain or added water. The results are summarized here:
A deep root zone is essential, and all sod grown on 4-inch root zones was killed out. Bermudas had the best tolerance and survival. Only Floratam St. Augustine did well in its group; however, Palmetto cultivar was a little more tolerant than Raleigh. Browning (leaf firing) occurred in about 30-35 days, 45 days and 50 days respectively for zoysias, St. Augustines and Bermudas. To avoid this browning, irrigate 1 to 2 weeks prior to these limits.
Of the Bermudas tested, Tifway 419, Texturf and Celebration fared best. In Zoysias tested, Palisades, Empire, El Toro and Jamur were the better survivors. Good recovery from the 60-day test took 2.5 to 3 weeks of adequate moisture for the Bermudas, a month for St. Augustines and 5 to 6 weeks for zoysias.
Keep It Green?
It is possible to keep a lawn green with minimal amounts of water if desired. Lawns generally need about one inch of rain or water per week to stay green and charged up, so supplement slight rainfall with irrigation whenever it is needed. Irrigate every seven to 10 days in summer as needed to avoid loss of bright green color, applying about 0.5-0.75 inch of irrigation water. This can be measured by leaving a tuna can or rain gauge on the lawn as you irrigate and measuring the contents after irrigating. Irrigation should be performed in the early morning to reduce the potential for fungal diseases and get best use of the water. If turf growth is continuous throughout summer, be sure to keep up the fertility as recommended for that species.
(Adapted for Louisiana from the Lawn Institute and TAMU's 2008 Final Report SAWS&TPT).