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84 WINES&VINES May 2018 GRAPEGROWING WINE EAST I n his book on viticulture, Pierre Galet noted that the grape botanical family (Vitaceae) exists in the fossil record in the Early Cre- taceous Epoch (66-145 million years ago), with examples of the genus Vitis found in the Early Eocene era 34-56 million years ago. 2 Geologists tell us that this was a time of the super-continent Pangaea, whereby plate tec- tonics subsequently drifted into a broader array of climatic regions, which placed further selection pressures on the offspring of those species. Nature Vitis survived in nature because natural selec- tion allowed their genotypes to adapt and suc- ceed in their environment. The genotypes best "fitting" that environment of growth produced more viable seeds and favored the resulting offspring. Grapes, as food, attracted animals to consume the berries and deposit seeds in other locations where natural selection contin- ued, and processes of adaptation occurred and resulted in the array of Vitis species. These species range in diversity from acidic soils (V. rupestris, V. riparia) to alkali flats (V. Berlandieri) and sub-tropical climates (V. vinif- era) to the -40° C line (V. riparia; V. amurensis) common to many hardy woody perennials. 3 Clearly, grapevines existed alongside dinosaurs and millions of years before our genus of homi- nids migrated out of Africa and began to play a part in the gathering and culture of the fruit and processing of grapes into wine. The evolution of Vitis contributes consider- ably to our understanding of the series of adap- tive grapevine physiological processes we collectively call cold hardiness. 4 What is grape- vine cold hardiness? Cold hardiness describes the ability of a grapevine to perform the follow- ing processes relative to its specific location: a) mature and initiate bud, cane, and perennial vine tissue prior to the earliest autumn freeze episodes (ac- climation); b) achieve adequate levels of freeze damage resistance during the cold- est winter freeze episodes; c) display resistance in response to dormant season warm temperature fluctuations that cause reduction in freezing resistance (mid-winter maintenance); and finally, d) slowly decline from maximal mid- winter hardiness as local conditions become more favorable for bud burst and shoot growth after the final spring frost (de-acclimation). Thus, cold hardiness is a localized response of the vine to its natural environment. Despite a cold-hardy vine's ability to withstand low tem- peratures, severe mid-winter freeze events can injure tissue. In addition, a freeze event occur- ring outside of the normal winter season, either during the hardiness transitional periods of Cold Hardiness of Grapevines How growers can encourage it given the limits of nature and nurture By Paolo Sabbatini, G. Stanley Howell and Josh VanderWeide Canes collected during the winter; on the left, a golden-brown periderm suggests good maturation and an elevated degree of cold hardiness; on the right, a light-colored periderm is probably the result of canopy shading, poor storage reserve and a reduced cold hardiness of the tissues. KEY POINTS Grapevines have evolved into a number of species, some of which are more tolerant of cold weather than others. The ability of a grapevine to acclimate to the arrival of cold weather, resist freeze damage and fluctuations of temperature while dormant, and then de-acclimate slowly for bud burst and shoot growth comprise what is known as "cold hardiness." The most important considerations for growers are the characteristics of a potential site, followed by the selection of varieties that are appropriately cold resistant, can ripen the fruit within the available timeframe, and are on rootstocks that can achieve the desired vine vigor. Vine spacing, training, water and nutrition are other parameters that must be considered. Once the site is selected and the vines planted, management goals should focus on the penetration of sunlight to the leaves. Training, pruning, leaf removal and shoot positioning should create an adequate exposed leaf area to mature the season's grapes as well as the canes for the next year's fruit. The grower should manage the vines to allow for maximum expression of the cultivar's genes for cold hardiness.