OLATHE, Kan. – If central U.S. lawns are looking faded or patchy and increasingly wheat-colored, that’s because most area homeowners grow cool-season turfs – tall fescue or Kentucky bluegrass.
Unless irrigated regularly, those turfs normally go dormant in summer. But, July’s weather has been so extreme that even some well-watered lawns are now slipping into dormancy, said Rodney St. John, K-State Research and Extension turfgrass specialist.
“Lawn management needs to be in survival mode, not problem-fixing mode. Excess thatch or compacted soil may be making the situation worse, but it can wait until fall. Right now, we need to concentrate on keeping grass alive,” St. John said. “What that means in terms of watering, however, depends on how ready the turf was for little to no rain and triple-digit heat.”
This is the second year in a row Kansas lawns have faced a stressful summer, he said. Ironically, the stress has been hardest on lawns that homeowners babied through spring.
| Be Slow to Mow in Hot Weather
Mowing during extremely hot weather adds to lawns’ stress, according to Rodney St. John, turfgrass specialist with K-State Research and Extension.
“When it’s as hot as the weather has been this July, mowing will even stress out warm-season turfs, such as bermuda, zoysia and buffalograss. But, their stress isn’t nearly as severe as what happens to cool-season grasses,” St. John said. “Fortunately, grass blades don’t elongate much in hot weather, so you may be able to put off mowing until the temperature cools a bit – preferably into the lower 90s or upper 80s F.”
When homeowners do mow, they should set their mower at the high end of their turf’s recommended cutting-height range, the horticulturist added. For warm season turfs, that height is about 2 inches. For cool-season grasses, it’s 3.75 to 4 inches tall.
“If your lawn is strong and healthy when it enters dormancy, you can quit watering the weeds. That kind of turf can go up to a month between waterings and still keep its crowns alive,” St. John explained. “But, if you or the weather watered the lawn incorrectly through spring – too much or too often – shutting the turf off ‘cold turkey’ could cause damage and even plant death.
“That’s what happened to many lawns last year. They had short-short roots, resulting from too-frequent spring rains. They weren’t prepared for the weather’s rapid turn to high heat and drought. Their root systems couldn’t supply enough water for plant growth and cooling – enough to allow the plants to enter dormancy gracefully. So, many turf plants died.”
For homeowners whose lawn is suffering now, he suggests waiting about seven days after its last good drink and then irrigating.
“If the lawn still has some green then, you can continue watering, or you can ease it into dormancy – your choice,” the horticulturist said. “If you decide on dormancy or your turf already looks dormant, you should extend the interval between waterings several days at a time until you’re on a two-week schedule. Your lawn probably won’t be tough enough to go any longer than that this year.”
In general, he said, the rule of thumb for lawns in Kansas is to ensure they get an inch of water per week. But, that rule varies in line with weather extremes.
“Given this July’s weather in most of the state, maintaining a green lawn and preventing dormancy required applying about an inch of water every three to four days,” St. John said. “In contrast, when the weather cools in fall, that rate will decrease, eventually reaching an inch every couple of weeks.”
Watering: How Deep, How Often
The turfgrass specialist has just posted several short “how-to” videos on the Web. They demonstrate such tricks of the trade as:
* Calculating when a lawn actually needs water, using local rain and evapotranspiration data reported daily by such services as the Kansas Weather Data Library.
* Measuring how deeply water has soaked in.
* Checking whether a sprinkler or irrigation system is distributing water evenly to all parts of the lawn.
* Figuring how long a particular watering system must run to deposit an inch of water.
* Reducing the water lost to evapotranspiration, as well as the odds for turf diseases.
St. John said the videos emphasize two rules of thumb for turf health: 1) water deeply and infrequently (i.e., promote deep root growth) and 2) monitor your soil moisture and the weather to estimate how much you should irrigate.
If lawns are at risk now, their owners may very well have been breaking one or both rules, he said.
In fighting to save their lawn, however, homeowners must not neglect any thin or bare spots, the horticulturist said. Spots that look like goners need moisture as much, if not more than turfed areas.
“To understand why, just place your hand on some green grass. Then place your hand on dried-out turf. The difference in temperature will be considerable,” St. John said. “In fact, dormant or dead turf’s heat can bake any adjoining green grass. To counter that, you have to water properly everywhere.”
K-State Research and Extension has a turfgrass information site on the Web. It contains links to a variety of lawn-related materials, as well as the blog for turfgrass professionals that St. John maintains with K-State plant pathologist Megan Kennelly.