The annual cycle of growth of northern highbush blueberry
In the fall, blueberry bushes are dormant and ready for winter. The blueberry bush uses the clue of shorten day length in the late summer to prepare for winter. The next is lower temperatures near freezing. Freezing temperatures are the final clue and the bushes go dormant waiting for winter. As long as cold weather does not arrive abruptly, we have little to worry about. The varieties we grow could easily handle cold temperature down to 0°F. If the temperatures are below freezing, then the plant can acclimate to the cold and its cold hardiness increases. The maximum cold hardiness for most Michigan varieties is about -18°F. At temperatures below -18°F, we begin to see flower buds die. At colder temperatures, we will see winter injury to leaf buds and shoots.