Most blueberry bushes can withstand temperatures as low as -20 degrees Fahrenheit. According to the Northwest Berry and Grape Information Network, some blueberry breeders in the northern United States have produced blueberry bushes that can tolerate temperatures as low as -40 degrees, if there is enough snowfall. Blueberry bushes require adequate winter protection in cold regions to protect against injury.

Site and Plant Selection

Select blueberry bushes that are adapted to the climate in your region for best results. Choosing bushes that are able to withstand the coldest temperatures your region receives is one of the most important steps in preventing winter plant injury. The United States Department of Agriculture (USDA) Plant Hardiness Zone Map separates the United States into hardiness zones based on the average minimum temperatures. Consider the lowest temperatures your region receives in addition to the average minimum temperatures represented on the Plant Hardiness Zone Map when selecting your blueberry bushes. If your area frequently experiences lower temperatures than the average, choose blueberries that are classified one zone hardier than yours.

Acclimation

Blueberry bushes go through a process called acclimation, as temperatures drop gradually in the fall and early winter. Bushes that are actively growing can be damaged at temperatures around 28 degrees, according to the Northwest Berry and Grape Information Network. Once blueberry bushes are exposed to cold, but non-lethal, temperatures for several days in a row they will reach maximum cold hardiness. Do not fertilize too late in the fall or over-fertilize your bushes during the growing season to prevent new growth late in the growing season. Late growth can slow the cold acclimation process and increase the risk of freezing injury. Do not prune blueberry bushes before they enter the dormant stage. Pruning in late fall can stimulate new growth and cause de-acclimate. Wait until the late winter and early spring months to prune blueberry bush canes so that you can remove any injured buds and braches from winter freezes or early spring frosts.

Mulching

Prepare your blueberry bushes for winter by mulching them before temperatures drop too low in the fall and the acclimation process begins. Many cold injuries that can kill blueberry bushes are related to root freezing injuries when the ground hardens and freezes around the bushes' root structure. Make a bed of bark, sawdust and mulch around your individual bushes to help control ground temperatures around the roots and hold heat in during the winter months.

Source:

North Dakota State University: Questions on Blueberry

Northwest Berry and Grape Information Network: Winter Acclimation and Cold Hardiness of Blueberry