It may be of interest that temperate zone perennial fruit crops actually require a cold dormant period to effect the necessary hormonal changes the plants need to initiate fruit bud-break in the spring. Northern hardy blueberry varieties can require more than 2,000 cumulative hours of annual chill (temperatures below +40F) for proper function. That said, perennial fruits in some years can be damaged when subjected to severe conditions.
It should provide some comfort to know that the varieties that knowledgeable growers plant at Bayfield are appropriate for our climate--in the case of our blueberries, most varieties are hardy to -30F or even colder when the plants are fully dormant. In addition, our Lake Superior peninsular climate at Bayfield mitigates the extremes of temperature. The coldest temperature recorded at Highland Valley Farm so far this winter has been -22F, that is 10 to 15 degrees warmer than our neighbors inland, or to the west of us in Minnesota, experienced this season. Also, the cold has been consistent with no erratic fluctuations or prolonged mid-winter thaws. Finally, we are normally favored with a deep insulating snow cover that most years comes early and stays late. This year the snow cover is exceptional, measuring 42 inches settled on the level in our open fields in February. As cold as it has been, there is little to no frost in the ground on our sandy soils, and even 2/3 of the branches of our plants have been covered for most of the winter.
It all depends on what happens over the next several weeks. Cold injury most often occurs during the late winter period in years when temperatures are erratic or "unseasonable". Plants that have accumulated sufficient chill will respond to warm ambient temperatures--especially as snow cover is lost--and will break dormancy. A return to colder temperatures after a loss of plant dormancy can result in injury and reduction of crop in the coming season.
Earlier this month I sectioned fruit bud samples from our fields to determine the extent of this season's winter cold injury to date. The degree of injury was minor in most varieties. Compared with samples taken on the same date from the preceding season's relatively mild winter, the level of injury for the current winter season is less. Last year's blueberry crop was normal. This year's crop could be as good or even better. I am optimistic, but then I am a farmer.