Blueberry bushes are deciduous shrubs that require a period of cold rest, known as chilling hours, to produce a successful crop of fruit the following season. The plant needs a specific number of hours below 45 degrees Fahrenheit to properly set its flower buds for the spring harvest. Proper winter care ensures the plant successfully completes this necessary dormancy and maximizes its potential for fruit production.
Preparing for Dormancy
Fertilization must cease by late summer or early fall to prevent a flush of tender new growth. This soft growth cannot harden off before freezing temperatures arrive and is highly susceptible to winter damage, which can weaken the entire plant.
Ensuring the soil has adequate moisture before the ground freezes solid prevents winter injury. Blueberries have shallow, fibrous root systems that are particularly vulnerable to desiccation from cold, dry winds. Watering deeply until the ground is frozen helps insulate the roots and provides a reservoir of moisture throughout the dormancy period.
Blueberries are acid-loving plants, thriving in a soil pH range of 4.5 to 5.5, and this acidity must be maintained year-round. Fall is an excellent time to test the soil pH and make small adjustments, such as adding elemental sulfur, before spring growth begins.
Protecting Bushes from Winter Extremes
Physical protection focuses on insulating the roots and shielding the canes from harsh weather. An organic, acidic mulch, such as pine needles, pine bark, or wood chips, should be applied two to three inches deep around the base of the plant. This layer insulates the shallow root zone, preventing deep freezing or repeated freeze-thaw cycles that cause frost heave.
Windbreaks are important because strong winter winds can cause desiccation and windburn on the canes. Wrapping smaller or younger bushes loosely with burlap or placing them behind a temporary barrier can reduce this exposure. Additionally, the bark of blueberry bushes is attractive to pests like voles, rabbits, and deer when other food sources are scarce. Protecting the lower canes with a physical barrier, such as a cylinder of hardware cloth or chicken wire, can prevent bark-stripping damage that might girdle the plant.
Dormant Season Pruning
Pruning is a winter task, ideally performed in late winter or very early spring while the bush is fully dormant, before the buds swell. This timing allows the grower to assess and remove any wood damaged by winter cold. The main goal of pruning is to stimulate the growth of new, productive canes, as blueberries produce the best quality fruit on one-year-old wood.
The first step in pruning is to remove any low-lying branches that touch the ground, along with dead, diseased, or crossing canes. For mature bushes, remove a few of the oldest, least productive canes each year, typically those five years or older that appear thick and grayish. Removing these older canes at the crown encourages new, vigorous shoots to grow from the base. This thinning process also opens up the center of the bush to improve air circulation and sunlight penetration, which helps prevent disease and increases fruit quality.
Winter Care for Container Blueberries
Blueberry bushes grown in containers require distinct care because their roots lack the insulation provided by the surrounding earth. The exposed sides of the pot make the root ball far more vulnerable to freezing temperatures than in-ground plants, risking damage or death when temperatures drop significantly below freezing.
The most effective protection involves relocating the potted bush to a sheltered, unheated area, such as a garage, shed, or cold frame. This location must remain cool enough to satisfy the plant’s chilling hour requirement but protect the roots from the most severe cold. If relocation is not possible, the pots can be insulated by grouping them tightly together against a building, wrapping them in burlap, or sinking the entire pot into the ground and covering the exposed soil with a thick layer of mulch.
During this dormant storage, the plant still needs minimal water to prevent the root ball from drying out completely. The soil should be checked monthly and lightly watered only if it feels dry an inch or two below the surface. Overwatering during dormancy is a risk, as the cold, soggy soil can lead to root rot.