Grapevines, such as the widely cultivated Vitis vinifera, are perennial woody plants with strong natural defenses against winter. The answer to whether grapevines die in winter is generally no, but this period poses the greatest risk to their health and future productivity. They transition from active growth to a state of deep rest, allowing them to survive temperatures far below freezing. Understanding this survival mechanism and the factors that influence it is important for anyone growing grapes.
The Biological State of Dormancy
The grapevine’s primary strategy for surviving winter is entering dormancy, a programmed suspension of visible growth. This process is initiated in late summer and early fall, triggered by decreasing day length and cooler temperatures, a mechanism called acclimation.
During acclimation, the vine prepares for the cold by shedding leaves and stopping the transport of water and nutrients to the shoots. The plant stores carbohydrates, mainly starches, into permanent woody structures like the roots, trunk, and canes. These reserves maintain basic metabolic functions throughout the winter and fuel rapid growth in the spring.
Dormancy has two phases: endodormancy and ecodormancy. Endodormancy is controlled by internal regulators and prevents growth even if external conditions are temporarily warm. Once a specific chilling requirement is met, the vine enters ecodormancy, where growth is held in check only by cold environmental temperatures.
Factors Determining Cold Tolerance
A grapevine’s ability to survive winter is determined by genetics, the specific tissue, and the timing of the cold event. Different parts of the vine have varying levels of cold hardiness; woody tissues of the trunk and canes are generally more tolerant than the buds.
The compound bud, which holds the potential for the next season’s crop, is the most vulnerable point. It consists of a primary bud, a secondary bud, and a tertiary bud. The primary bud is the least winter-hardy, often dying at temperatures that do not damage the cane itself. Woody tissues like the phloem and vascular cambium are also susceptible to injury, especially during sudden temperature drops.
Genetic background is the most important factor determining hardiness. Vitis vinifera, the European wine grape species (e.g., Chardonnay), is cold-sensitive, with mid-winter temperatures below 0°F potentially causing damage. American species like Vitis labrusca (e.g., Concord) and their hybrids are significantly more cold-hardy, sometimes surviving temperatures as low as -25°F depending on the cultivar.
The timing of a cold event is also significant. Vines are most cold-hardy during peak mid-winter dormancy, typically December through February. Cold snaps that occur before full acclimation in the fall or after de-acclimation in late winter pose the greatest threat. Warm spells during winter can cause the vine to lose hardiness quickly, making it highly susceptible to severe injury if cold weather suddenly returns.
Practical Steps for Winter Protection
Preparing grapevines for winter involves management practices that encourage maximum cold hardiness. Late-season care should focus on allowing the vine to naturally slow its growth and allocate energy reserves. Avoid late-season nitrogen fertilization, as this stimulates tender growth that will not harden off before frost.
Home growers in colder climates often use physical protection methods. For young or grafted vines, mounding soil around the base of the trunk (hilling) protects the graft union and lower trunk. In regions with extreme cold, some growers untie canes from the trellis and bury them under soil or insulating mulch like straw.
Pruning should be timed carefully to avoid stimulating premature growth, as fresh cuts increase susceptibility to cold injury. Delay major pruning until late winter or early spring, just before bud break. This timing allows the grower to assess winter bud damage and adjust pruning severity to compensate for dead primary buds by retaining more wood.
Identifying and Addressing Winter Damage
After the threat of severe cold has passed, assessing the vine’s health is important for final pruning and management decisions. The most common diagnostic method involves inspecting the compound buds for viability. Using a sharp blade to slice a cross-section of a dormant bud reveals the tissue color inside.
Healthy, living tissue within the bud appears bright green, while damaged or dead tissue has a brown or blackish hue. If a significant percentage of primary buds are dead, the grower compensates by leaving more dormant buds during pruning. This relies on the hardier secondary or tertiary buds to produce a crop.
Damage to permanent wood, such as the trunk or canes, is identified by scraping away outer bark to expose the underlying tissue. Brown or gray discoloration indicates injury to the vascular tissue, which impairs the vine’s ability to transport water and nutrients in the spring. If the trunk is severely damaged, the best strategy is to train a new shoot (“sucker”) from healthy tissue near the ground to replace the injured trunk.