Critical lethal temperatures and growth stages for grape growers


21 Apr 2017

As we enter into the bud break development period please refer to the following table for critical lethal temperatures and growth stages as vines are now reaching these developmental stages across the Ontario.  This table provides guidelines for cold protection measures for grapes during this critical stage.

For optimal use of wind machines, it is suggested that the start-up temperatures be set at 2 to 3 degrees warmer than temperatures at which injury might occur. It is also important to monitor wind speeds along with temperatures.


Growth stage Critical temperatures Suggested Temperatures for start-up of wind machines
Dormant bud Minus 5 C (as of April 17, 2017) Minus 2 to Minus 3C
Dormant swollen bud Minus 3 C Minus 1  to 0 C
Bud Burst Minus 2.2 C 0 C to Plus 1 C
One leaf unfolded Minus 1.5 C Plus 1 C to Plus 2 C
Two or more leaves unfolded Minus 1 to 0 C Plus 1 C to Plus 2 C


Cold hardiness ratings are estimates only and the information provided is for general guidance. Cold hardiness ratings are site specific and may vary based on vine health, viticulture practices and site conditions, among other factors. Any decisions for protection strategies should be based on your own information and site conditions.  These guidelines are based on going research at Brock and the team at CCOVI.



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