Grapevine Cold Hardiness
Ed Hellman
Texas Cooperative Extension
In autumn, the grapevine enters dormancy - the stage with no leaves or growth activity, which extends until budburst the following spring. Despite the apparent inactivity of this stage, it can be a critical time for grapevines when they may be exposed to potentially damaging low temperatures. The ability of a dormant grapevine to tolerate cold temperatures is referred to as its cold hardiness. Grapevine cold hardiness is a highly dynamic condition, influenced by environmental and growing conditions, and varying among grapevine varieties and tissues, and over time. Therefore, cold hardiness cannot be viewed or described in absolute terms such as “Variety X is cold hardy to minus 8oF”. The ability of green leaves and shoots to tolerate cold temperatures is usually referred to as frost tolerance.
Howell (2000) describes three stages of the dormant season: acclimation, the period of transition from the non-hardy to the fully hardy condition; mid-winter, the period of most severe cold and greatest cold hardiness; and deacclimation, the period of transition from fully hardy to the non-hardy condition and active growth. Acclimation is a gradual process, beginning after shoot growth ceases and continuing through autumn and early winter. The combination of declining day length and decreasing temperatures in autumn are important factors influencing acclimation and cold hardiness (Wample, et al., 2000). The process of acclimation in grapevines is not well understood, but it involves many simultaneous activities that collectively increase cold hardiness. Water content of some tissues decreases, while increases occur in cells’ solute (dissolved solids) concentration, membrane permeability, and the thermal stability of several enzymes (Mullins, et al., 1992).
Howell (2000) has reviewed the mechanisms by which grapevines survive cold temperatures. The primordial tissues of dormant buds survive by avoiding the formation of ice crystals in the tissue by supercooling - a process by which a liquid remains fluid below its normal freezing temperature. Other tissues survive by increasing their capacity to tolerate both ice in the tissue and increased concentration of solutes in the cell. Increased solute concentration in the cell lowers its freezing point.
Because of the different mechanisms involved, tissues vary in tolerance to freezing temperatures. Woody tissues of the trunk, cordon, and canes generally have greater cold hardiness than dormant buds and roots (Howell, 2000). In comparisons of grapevine woody tissues, the vascular cambium is thought to be the last tissue to be damaged by cold temperatures, followed in sequence by younger xylem, older xylem, and phloem (Wample, et al., 2000). Within dormant buds, primary buds are typically less cold hardy than secondary buds, and tertiary buds are the most hardy.
Species and varieties of grapes exhibit a broad range of potential cold hardiness based on their inherent genetic characteristics. This fundamental genetic potential for cold hardiness is influenced by both environmental conditions and the circumstances under which the vine grew in the previous season. Poor management practices or growing conditions can inhibit the acclimation process, resulting in reduced cold hardiness. Acclimation is promoted by exposure of shoots and leaves to sunlight, and is associated with periderm development and low relative water content (Mullins, et al., 1992). Cold hardiness was found by Howell (2000) to vary considerably between and within vines. Reduced hardiness was associated with large, dense (shaded) canopies; canes with either long internodes and/or large internode diameter; and canes with large persistent lateral canes. Additionally, heavy fruit loads or defoliation (early leaf fall due to stress, disease or pest activity) inhibits acclimation, probably through reduced availability of photosynthates (Mullins, et al., 1992). Contrary to popular belief, neither nitrogen fertilization nor irrigation practices reduce grapevine cold hardiness, unless nonstandard practices are used that encourage continued late-season growth, which inhibits acclimation (Wample, et al., 2000).
Cold hardiness of buds is fairly stable through the winter months, but sharp increases in temperature can cause buds to deacclimate and lose hardiness, and the extent of deacclimation can vary by variety or species (Wolf and Cook, 1992). Bud hardiness of Riesling, Cabernet Sauvignon, and Concord was strongly correlated with air temperature of the preceding 5-day period. Cold hardiness decreases as the grapevine rapidly deacclimates in response to warm temperatures in the spring. Deacclimation is much less gradual than cold acclimation in the fall, and the rate of deacclimation accelerates through the dormant season (Wolf and Cook, 1992).
Additional Resources
Cold Damage in Grapes
Washington State University
Cold Hardiness - Current Season Data
Washington State University
Anatomy of Winter Injury and Recovery
Cornell University
Assessing and Responding to Winter Cold Injury to Grapevine Buds
Cornell University
Dealing with Winter Cold Injury to Grapevine Canes and Trunks
Cornell University
Cold Hardiness of Grapes:
A guide for Missouri growers
Missouri State University
Frost Damage
How Cold Can Grapes Go?
Michigan State University Extension
Preventing Vineyard Frost Damage
University of California Cooperative Extension, Tulare County
Microsprayer Frost Protection in Vineyards - Research Report
California State University, Fresno
Passive Frost Protection of Trees and Vines
University of California Cooperative Extension
References
Howell, G.S. 2000. Grapevine cold hardiness: mechanisms of cold acclimation, mid-winter hardiness maintenance, and spring deacclimation. Proceedings of the ASEV 50th Anniversary Meeting, Seattle, Washington. Pp. 35-48.
Mullins, M. G., A. Bouquet, and L. E. Williams. 1992. Biology of the Grapevine. Cambridge University Press.
Wample, R.L., S. Hartley, and L. Mills. 2000. Dynamics of grapevine cold hardiness. Proceedings of the ASEV 50th Anniversary Meeting, Seattle, Washington. Pp. 81-93.
Wolf, T.K. and M.K. Cook. 1992. Seasonal deacclimation patterns of three grape cultivars at constant, warm temperature. American Journal of Enology and Viticulture 43:171-179.
