Well, the polar vortex lingers on and the posts on the GLFW site keep coming. This one is especially relevant, with information on other perennial fruits, as well. There is also mention of losing cold hardiness with warmer winter temps. Didn’t I see that we may hit 40degrees by Saturday? Mark has a link to the weather temps around Michigan. Is this something available for Door Co. through Matt Stasiak’s project? Or is there another such source? If you have it, please post as a comment!
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Nice discussion, I was planning on writing an article on cold hardiness, now I think I can write 3 or 4.
When we speak of winter injury we are speaking about a lot of different tissues in the plant. I will confine this to buds and not stems and roots.
I don’t believe the wind chill matters much except by desiccation. What matters is the air temperature and cold duration.
Since we got down to -19 to -17 F (-27 to -28 C) last Thursday (Jan 3), I expect we will have a light peach crop in Michigan this year especially away from Lake Michigan. I also expect to see damage in vinifera grapes and blueberries and a lot will depend on Variety and site.
My rule of thumb is that most of our fruit crops can handle 0F or -18C during the winter as their minimal cold hardiness. Below zero I start to worry. If the weather has been really cold below freezing for several days I don’t worry unless the temps drop to -10F then I start to worry about peaches, blueberries and wine grapes.
If the temperature has been above freezing recently the plants have lost cold hardiness. My rule of thumb is 2 days above freezing meaning the night time low was above freezing and the plants will have lost all their acclimation to cold weather and be back to the 0F damage threshold.
The 0F threshold is only for cold tender (a relative term) plants such as peaches, wine grapes and blueberries.
More cold hardy are cherries and European plums with apples and pears being the most hardy.
-20 to -25F will have an impact on Prunus and apples and pears should be able to go to -25 with little damage.
If the high or low temperatures drop more than 50F, I worry, 70F I really worry. This means we had a lot of free water in the plant (or as the growers would say the sap is up) and it froze real fast and I think damage is likely.
Here is a link to the temperatures we had in SW Michigan last Thursday morning.
http://www.enviroweather.msu.edu/run.php?stn=tpd&mod=w_nt&da1=3&mo1=1&da2=3&mo2=1&yr=2014&ds=cd
This table shows the hourly temperatures. If you do not know the locations the numbers about -10 are in high areas and those below -15 are in low areas. We had a light breeze from the south that night so the Lake Effect was not apparent.
Michelle, Temperate Zone Pomology has a good discussion of acclimation and cold hardiness; it is my bible for this stuff.
I am glad I am not Jon in Massachusetts! Fortunately we did not get above freezing before the cold air came back. I expect significant damage on the East Coast from the warm rain to the frigid blast
This is the second coldest blast in my 20 years here in Michigan. In 1994, we got to -24, -28F (-31 to -33C)in February  it was so cold the brine was freezing in the pickle vats. We saw many young trees killed outright. Wine grapes killed to the snowline. Tart cherries that were defoliated early died and did not leaf out. No peaches and damage to the lower trunks above the snow where the air is coldest and the temperature differential is the most. Older peaches and plums began to lose leaves during the first dry spell and declined for several years after. Many juice grapes leaved out normally and then collapsed during the summer. We had dead flower buds in all crops including apples but other than peaches, wine grapes and blueberries the state crops were normal. I would suggest that each of us try to record as many observations as possible and share them to give us a better picture of what has happened.
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Mark Longstroth
MSUE Small Fruit Educator
Office (269) 657-8213 ext 3
Cell     (269) 873-8983
Twitter MIBluedoc
Michigan Blueberry Facts http://blueberries.msu.edu/
