A Need for Hardiness

Happy New Year! What better way to kick-off than looking at how turfgrasses adapt to cold temperatures.  What affect have the blistering temperatures doing to plants specifically turfgrasses?  The good news is during early January turfgrass plants are their most hardy when it comes to cold temperatures.  The cold tolerance of turfgrasses varies among species but in general cool season turfgrasses are more cold tolerant than warm season turfgrasses (Table 1).

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

Given the temperatures in Table 1, you may think a number of turfgrass species especially warm season turfgrasses may be at risk if the reported low temperatures.  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.  The crown is often situated at or below the soil surface so soil temperature impacts the survival of the crown than air temperature.  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. 

 Unfortunately, the cold temperatures in January often extend down into the southern United States where warm season turfgrasses are grown.  The same avoidance mechanisms exist for warm season turfgrasses as cool season turfgrasses. 

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

However, there are some areas where warm season turfgrass loss is a potential concern on golf courses and homelawns.  One way to check to see how the turf is doing is to 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.

What about ornamentals?

Most plants are their most cold hardy at this time, but I would be most concerned with the potential for sun scald during January.  Sun scald occurs during cold sunny days during winter.  Trees like maple, plum, cherry and linden, and newly planted trees are especially susceptible.  A common scenario for sun scald occurs when the sun’s radiant energy warms the bark to the point where cambial activity occurs.  If temperatures drop quickly from the sun being blocked by clouds, or at sunset the tissue could be killed.  Symptoms of sun scald are characterized by sunken, dried or cracked areas of dead bark.  The symptoms usually appear on the south or southwest side of a tree where the sun has warmed that portion of the trunk.  To repair sun scald damage, cut the dead bark back to the live tissue, rounding off any sharp corners to facilitate healing.

So as you try to stay warm this winter, don’t forget to keep an eye on your turf and plant material.  Cold weather can affect them too.

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