The garden strawberry, Fragaria × ananassa, is a perennial plant designed to survive winter by entering a natural state of rest known as dormancy. Strawberry plants do not die when temperatures drop; instead, this survival mechanism allows them to conserve energy and protect their most vulnerable parts until spring. Understanding this cycle is essential for gardeners to ensure a bountiful harvest the following season.
The Biology of Winter Survival
Strawberry plants initiate dormancy in response to shorter days and consistently cooler temperatures through a process called cold acclimation. This allows the plant to develop a natural tolerance to freezing conditions. The plant’s survival hinges on the central growing point, known as the crown, which is a compressed stem structure at the soil line.
During dormancy, the plant reallocates energy, withdrawing starches from the foliage and storing them in the roots for spring use. While unprotected plants can suffer injury at temperatures around 15°F, a fully hardened crown can withstand temperatures significantly lower, sometimes below -40°F. Older leaves often turn reddish-green and flatten out, signaling the plant has entered this hardy state.
The chilling requirement is essential for future fruit production. Strawberries must accumulate a certain number of hours, typically between 28°F and 45°F, to successfully break dormancy. Without sufficient chilling, the flower buds may open unevenly or not at all, which would significantly reduce the yield the following spring.
Preparing Strawberry Plants for Dormancy
Preparation for dormancy begins in late summer or early fall, well before the first hard frost arrives. The primary late-season task is renovation, which focuses on cleaning up the bed and modifying the plant structure. For June-bearing varieties, all old foliage should be trimmed back to a height of one to two inches above the crown.
This trimming can be done with shears or, for larger patches, a lawnmower with the blade set high enough to avoid damaging the crown. Removing the old leaves helps interrupt disease cycles and deprives pests, like mites, of a winter habitat. Gardeners must take care not to cut into the crown itself, as this structure is the source of all new growth.
The strawberry patch should also be thoroughly weeded and thinned out at this time. Removing excess runners and crowded plants ensures the remaining plants have adequate space to develop a strong crown and build up energy reserves. A light application of a balanced fertilizer in the late summer, at least a month before the first expected frost, encourages the plant to store energy in its root system for the winter.
Essential Winter Protection Methods
Physical protection is necessary once the plants have hardened off and the ground has begun to freeze, usually in late November or early December. Applying insulation too early can trap moisture, which may lead to crown rot, or prevent the plants from fully acclimating to the cold. The ideal time to apply a protective layer is when the top half-inch of soil is frozen or when daytime temperatures consistently drop into the 20s.
The most effective material for winter protection is loose straw or pine needles, which should be spread to a depth of four to six inches over the entire bed. This layer of mulch provides insulation, helping to keep the soil temperature stable and preventing the repeated freezing and thawing cycles that cause soil heaving. Heaving can push the strawberry crowns out of the ground, exposing them to desiccating air and root damage.
Protecting Container Plants
For strawberries grown in containers, the roots are more susceptible to freezing temperatures because they are exposed above ground. Potted plants can be moved into an unheated garage, shed, or cold frame for the winter. Alternatively, the pots can be buried in the ground to insulate them, or large planters can be wrapped with burlap and insulated with straw. Container plants stored indoors should be checked periodically to ensure the soil remains barely moist, as they will still require minimal water while dormant.
Transitioning Plants Out of Dormancy
The transition back to active growth begins in the spring when new green leaves start to emerge from the crown. Monitoring the plants for this new growth is the signal to start removing the protective winter mulch, usually after the danger of hard freezing temperatures has passed.
The mulch should not be removed all at once, as a sudden shock of cold air or intense sunlight can damage the emerging leaves. Instead, the process should be gradual, pulling back enough of the material to expose the newly developing foliage. The excess straw or pine needles should be placed in the walkways between the rows, where it can serve as a weed barrier and keep the developing fruit clean.
Leaving a thin layer of mulch over the crowns helps slow the warming of the soil, which can delay blooming by a few days. This delayed flowering protects vulnerable blossoms from late-season frost events. Once the plants are actively growing, apply a light feeding with a slow-release organic fertilizer or compost around the base of the plant, taking care to keep the crown uncovered.