Master Gardeners: Turfgrass response to winter fury may take weeks to determine
(Editor’s note: This is part one of a two part series.)
By Kay Ledbetter
Texas A&M AgriLife Extension Service
This is the first in a 2two-part series on your turfgrass and it’s survivability thru the past cold temperatures. Next week will be Part 2.
Many Texans are wondering how their turfgrass will respond come spring after Mother Nature unleashed the recent arctic snap across southern regions unaccustomed to such freezing temperatures.
The low temperatures experienced in many parts of Texas rivaled record lows not seen in over 100 years, but it was the sheer duration of sub-freezing temperatures that was more concerning, according to Texas A&M AgriLife Research and Texas A&M AgriLife Extension Service turfgrass experts.
Chrissie Segars, Ph.D., AgriLife Extension turfgrass specialist, Dallas stated “Ironically, although the Houston area experienced 1-degree wind chills, these frigid temperatures were only the lowest on record since 1990.
“Perhaps the one blessing in disguise for plants during this event was the snowfall that came along with it, blanketing the state as far south as Brownsville, where measurable snow had only fallen twice since record keeping began over 120 years ago,” Segars said.
“Patience is key this spring, as delayed recovery and green-up may be expected from rhizomatous species including Bermuda grass and zoysia grass,” she said. “This is going to be the case where low temperature kill injured stolons/rhizomes near the surface, but regrowth may still be possible from deeper in the canopy where temperatures were stabilized near or above freezing during the multiday freeze event.”
Winter injury of warm-season turf
Winter injury of warm-season turfgrasses may arise due to numerous factors, including direct low- temperature kill or freeze injury, suffocation under prolonged ice cover, frost injury and desiccation during windy, dry conditions, said Ben Wherley, Ph.D., AgriLife Research turfgrass ecologist in the Texas A&M Department of Soil and Crop Sciences, College Station.
Of these, freezing injury due to exposure to prolonged low temperatures would be the greatest risk to grasses during an extended deep freeze like the one occurring recently, Wherley said. Although all warm-season grasses have some degree of built-in winter dormancy mechanisms, their relative tolerance to subfreezing temperatures goes only so far and varies depending on the species and cultivar.
Although Bermuda grass cultivars with enhanced cold tolerance have been developed in recent years, such as Latitude 36 and Northbridge, they generally possess moderate cold tolerance, limiting their use to the southern transition zone and southward.
Among the warm-season grasses, centipede grass, seashore paspalum, St. Augustine grass and ultra-dwarf Bermuda grasses, typically used on putting greens, all possess the least cold tolerance and are those of most concern following cold snaps like the one experienced recently.
Freeze resistance, survivability
So, what’s the difference between species or cultivars with high and low freezing resistance? The answer lies in a grass species’ ability to “harden-off” or acclimate during the fall months, as temperatures begin to drop going into winter, Wherley said.
During the acclimation process, freeze-resistant plants begin to dehydrate their cells by accumulating solutes, including sugars and ions such as potassium within the cell, which act in a similar way to antifreeze, explained he said.
“This is one of the major reasons we apply late-season applications of potassium to warm-season turf,” Wherley said.
Freezing injury, therefore, is most common in plants that have not acclimated, or are unable to acclimate to low temperatures, leading to ice formation within the cell and subsequent rupture of cellular contents, he said.
When assessing the potential for low-temperature injury, focus on temperatures at or near the soil surface during the period of concern combined with the duration of the subfreezing exposure.
“In the absence of snow, ambient air temperatures may be a good means of estimating soil surface temperatures,” she said. “However, if snow is present, as was the case with the recent cold snap, it insulates the turf, creating a physical barrier to heat loss which often keeps the turf near or even above freezing. In fact, this is the same reason that golf courses cover greens with winter blankets during subfreezing conditions.”
When considering low-temperature thresholds combined with the more than three days of subfreezing temperatures, the outlook for warm-season turfgrass survival and recovery would seem very bleak were it not for the timely snowfall that occurred and insulated the ground through most of the extreme cold.
“While it’s likely that spring green-up may be delayed in many areas and stands may be thinner than usual, we are cautiously optimistic that we will see favorable spring recovery of warm-season turf stands across much of South-Central Texas,” she said.
In the Bryan-College Station area, although air temperatures dropped into the single digits over multiple nights, upper soil temperatures never fell far below freezing, which may have aided the chances for warm-season turf survival, Wherley said. Winterkill of some of the more sensitive warm-season grasses begins in the mid 20’s.
For more horticulture questions please call the Orange County Master Gardener Hot Line at 409 882-7010 Tuesday and Thursdays 10 a.m. – 2 p.m. or email firstname.lastname@example.org.
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