Cold Hardiness of Grapevines Through Cold Acclimation

We have to look back to last year in order to understand how our grapevines are handling the winter cold. Vines gain cold hardiness as a result of decreasing temperatures. The colder the temperature, the more hardiness the grapevine gains up to a critical threshold that is determined by the following¹:

• Environment
• Cultural practices
• Genetic makeup of the cultivar

Grapevines begin their process of cold acclimation or the transition of the vine from a cold-tender to a cold-hardy state beginning in late summer. The following processes are already complete shortly after leaffall:

• Periderm formation
• Mobilization of carbohydrate reserves to canes, trunks and roots
• Isolation of dormant buds from the vascular tissues in canes and trunks

There are two basic stages of cold acclimation in grapevines that occurs before the onset of winter:

• First stage: induced primarily by low but above freezing temperatures (above 32 ^oF) and occurs in late summer to early fall before any freeze events
• Second stage: exclusively induced by temperatures below freezing and usually coincides with the first killing fall freeze in mid-October to mid-November

One question was answered for us on page 21 of the Michigan State University publication regarding windchill: Because dormant grapevines neither generate internal heat nor significantly evaporate water, windchill does not alter the temperature experienced by the bud. Reading about the processes of cold acclimation is somewhat reassuring but we still have to do the test for bud injury in order to access how the vines faired.
References:
1. Tom Zabadal, Winter Injury to Grapevines and Methods of Protection, Michigan State University, Extension Bulletin E2930, June 2007, pg. 7.