The polar vortex is dropping

This week will see rapidly dropping temperatures through the northern United States due to the polar vortex.  The polar vortex is a large low pressure area that occurs at both the north and south pole.  It extends about 620 miles in diameter and rotates counter clockwise.  It normally strengthens during the winter and remains over the arctic.  If it weakens, which it tends to do several times during a decade it will break uo into two or more small vorteces. The vorteces that impacts the United States the greatest is the one that centers around Baffin Island, Canada,

Figure 1.  Projected weather for the week of February 6, 2021.  

Polar vorteces have invaded the United States for a long time with the first reported one in 1853 and more recently in 2014 and 1019.  The 2014 I one was severe occurring from December through January.  During 2014 temperatures would drop well below -6 F in Columbus Ohio with much colder temperatures west and further north. The challenge this week is the cold temperatures are coming in February.  Whether the turf is cool season or woarm seaon, turfgrasses are their most cold tolerant in December and January.  As February arrives the cold tolerance hardiness begins to break.  In Table 1 the cold hardiness of turfgrasses reported occur at the plant's most hardened state.    

Given the reported temperatures, and the likelihood of turfgrasses beginning to lose some hardiness  a number of turfgrass species especially warm season turfgrasses may be at risk in the coming weeks.  However, turfgrasses have avoidance mechanisms that shield or protect them from direct exposure to potentially killing temperatures.  The growing point (crown) is often positioned where it is not exposed to killing air temperatures often situated at or below the soil surface.  Additionally, if a snow cover is present the temperature below the snow is warmer than the air temperature.  This example can extend to rhizomes and stolons where temperatures are buffeted by the soil and snow cover. 

Where extensive snow cover has occurred through the northern United Stattes,  this should provide protection to the turf, especially annual bluegrass turf. However this polar vortex blast will hit areas further south into areas like northern Texas, Tennessee, northern Alabama etc. where warm season turfgrasses like bermudagrass are present injury could occur.  The potential for increses for bermudagrass death occurs as cutting heights shorten.  

Check for winter injury  periodically bring some samples in and place them in a warm sunny area to see if the plants start growing.  An additional method is to inspect the crown to see if it is alive.  The crown is often hard to see but is located at the base of the plant.  Peel back the sheath and if the crown area appears white and firm the crown is healthy.  If the crown is brown and mushy that plant has or will die.

Figure 1.  Winter kill symptoms on off-type bermudagrass areas.

Figure 2.  Winter injury symptoms on a bermudagrass fairway located in the transition zone. 

About the author

Dr. Karl Danneberger is a professor of Turfgrass Science at The Ohio State University. Dr. Danneberger's contact information can be found here. You may also follow Dr. Danneberger on Twitter: @GlobalTurf