TURF CARE : Winter ’ s on the Way by Jason Lanier , Turf Specialist , UMass Extension
While the month of September is precious prime time for key turf management activities like planting , fertilization , and aeration , once the calendar turns to October forward-thinking turf managers begin to shift their attention to the oncoming winter . Shorter days and cooler nights remind us that winter is just around the corner . After the heat and drought of summer , the winter season is the most difficult test for our cool-season ( C3 ) grasses .
Most perennial warm-season ( C4 ) turfgrasses , such as bermudagrass or centipedegrass , are easily killed by lower temperatures and are therefore much better utilized in warmer geographic areas . Cool-season ( C3 ) grasses , like Kentucky bluegrass and perennial ryegrass , are well-suited for culture in the Northeast because they have an inherent ability to survive the winter conditions typical of this region . Different species and cultivars vary in their tolerance level however , and injury or death is still very possible under the wrong mix of circumstances . There are two basic mechanisms of turfgrass injury by low temperature , or what is often called direct low temperature kill :
◆ Intracellular freezing occurs when the temperature dips to the point at which ice crystals form in the fluid within plant cells . The sharp crystals rupture the cell membrane resulting in leakage and eventual death of the cell . When this phenomenon occurs within the turfgrass crown ( the main growing point of the plant ), death of the entire plant is likely .
◆ Extracellular freezing involves ice crystal formation outside of plant cells during low temperature exposure . The ice crystals create a negative potential gradient that draws water out of cells and leads to desiccation , cell collapse and death of tissue .
In response to shorter days and cooler temperatures in the fall , grass plants gradually shift resources away from growth and towards preparation for winter survival . During this acclimation to decreasing temperature ( hardening ), the ability of turfgrass plants to reduce crown hydration and accumulate solutes such as carbohydrates , soluble proteins and amino acids helps to protect plants from direct low temperature kill . The period after which shoot growth ceases , but the turf remains green ( typically around late November-early December in Southern New England ) is especially critical for acclimation . The bulk of the carbohydrates produced by photosynthesis during this phase , instead of being directed to growth , are used by each plant to protect vital cells from freezing . A gradual decline in temperature over a period of 3 or 4 weeks is preferable during the last stage of the hardening process . Although air temperatures often fluctuate ( sometimes considerably ), soil temperatures are buffered and therefore the descent is typically more measured .
As noted above , even among well adapted cool-season grasses , there is significant variability in low temperature tolerance and overall winter hardiness at both the species and especially the cultivar level . Genetics , furthermore , are only part of the equation , as a whole series of environmental , management and plant factors will play a role in the actual risk of cold injury any given year . In the end , much depends on the quality of acclimation and the timing and pace of de-acclimation come spring . A lot of frustration originates from the fact that many aspects of the process are beyond our control . Research is ongoing to increase our understanding of low temperature hardiness in C3 grasses .
( continued on p . 7 )
6 MLP Newsline | Fall 2021