HO-88

Kentucky Viticultural Regions and Suggested Cultivars S. Kaan Kurtural and Patsy E. Wilson, Department of Horticulture, University of Kentucky; Imed E. Dami, Department of Horticulture and Crop Science, The Ohio State University

rapes grown in Kentucky are sub- usually more harmful to grapevines than Even in established fruit growing areas, ject to environmental stresses that steady cool temperatures. temperatures occasionally reach critical reduceG crop yield and quality, and injure Mesoclimate is the climate of the vine- levels and cause significant damage. The and kill grapevines. Damaging critical yard site affected by its local topography. moderate hardiness of grapes increases winter temperatures, late spring frosts, The topography of a given site, including the likelihood for damage since they are short growing seasons, and extreme the absolute elevation, slope, aspect, and the most cold-sensitive of the temperate summer temperatures all occur with soils, will greatly affect the suitability of fruit crops. regularity in regions of Kentucky. How- a proposed site. Mesoclimate is much Freezing injury, or winterkill, oc- ever, despite the challenging climate, smaller in area than macroclimate. curs as a result of permanent parts of certain species and cultivars of grapes Microclimate is the environment the grapevine being damaged by sub- are grown commercially in Kentucky. within and around the canopy of the freezing temperatures. This is different The aim of this bulletin is to describe the grapevine. It is described by the sunlight from spring freeze damage that kills macroclimatic features affecting grape exposure, air temperature, wind speed, emerged shoots and flower buds. Thus, production that should be evaluated in and wetness of leaves and clusters. winterkill is much more costly, as entire the site selection process and to shorten plants can be destroyed, not just the the trial and error process of finding the Components of crop. Common injuries include winter best cultivar and climate match. sunscald, frost-splitting of trunks, death Macroclimate of dormant buds, stem blackening, and Climate Many prospective vineyardists will death of tissue in twigs, branches, and have a narrowly defined interest in vine- trunks. However, the injuries listed do Climate is defined as the prevailing yard site selection. Some regions in the weather of a geographic region. Prospec- not occur indiscriminately; many factors world have had hundreds and thousands of plant hardiness and health determine tive vineyardists must consider three of years to define, develop, and under- categories of climate: macroclimate, the probability and extent of such inju- stand their macroclimatic regions, but ries. Levels of damage from minimum mesoclimate, and microclimate. newer regions such as Kentucky typically Macroclimate is the climate of a large temperature exposure have been linked face a trial and error process of finding to tissue type, level of plant dormancy region measuring many square miles. the best cultivar and macroclimate For example, the lower Midwest region and season, mid-winter temperature fluc- match. The macroclimate is analyzed as tuation, plant size, wood maturity, and is characterized by a continental climate follows for viticultural purposes. where temperatures fluctuate on a day-to- cultivar hardiness. Hardiness is a product day basis. The macroclimate in Kentucky of not only the lowest temperatures that a Dormant Season plant can withstand but also how well the is characterized as humid and conti- Critical Low Temperature Frequency nental with severe winter temperatures plant acclimates to the winter conditions and warm summer temperatures. The Low temperature injury is the factor of an area. conditions in these climates are excellent determining the distribution of grape- The protection of cultivated plants for the growth of annual row crops. Most vines on earth. Many fruit species were against winter injury may present prob- rainfall occurs in the summer months. either bred for specific fruit quality factors lems not found in natural environments. However, in some years rainfall is sparse, or have been moved from the climate in Grapes have been subjected to severe resulting in drought. The fluctuation of which they evolved. Thus, many domestic winters and late spring frosts for thou- daily temperatures during midwinter is forms are not completely adapted to the sands of years, but many cultural prac- environment in which they are cultivated. tices exist that can augment the ability of fruit species to survive outside of their The frequency of critical temperature exposed to -15˚F may sustain 50 percent indigenous range. In general, the hardi- occurrence in a given region is the basis primary-bud injury, and possibly cane, ness of the major temperate fruit crops, for identifying minimum temperature cordon, or trunk injury. This threshold is from hardiest to most sensitive, is best hardiness zones. Advective freezes affect representative of moderately cold-hardy summarized as follows: the occurrence of minimum winter tem- hybrids (e.g. “Chambourcin”, “Chardonel”, peratures and therefore the commercial “Traminette,” and “Vidal blanc”) that are most hardy success of vineyards in Kentucky. predominantly grown in Kentucky. apple pear Radiative freeze events usually occur However, setting a critical threshold at plum during calm, clear weather as the ground -15˚F would not exclude injury at warmer cherry cools—by infrared radiation to space af- temperatures since cold hardiness varies peach/grape ter sunset. As the ground heat dissipates with cultivars, acclimation, and season. least hardy into the atmosphere, the ground becomes Figure 1 depicts the occurrence of -15˚F cooler and begins to cool the air directly between 1974 and 2005 in Kentucky. This means that most apple and pear cul- above it. Because the earth and air are The occurrence of -15˚F happens with tivars can withstand lower temperatures naturally cooler at higher elevations, varying regularity in Kentucky. Regions than can the peach or grape, and they they cool more quickly. Cold air is much that experience -15˚F less than 5 percent possess superior acclimation processes. denser than warm air and will actually of the time in a 30-year period are suit- However, great variation occurs within begin to flow in a viscous manner, from able for the most tender hybrid cultivars. and among each fruit crop; native and high to low areas, when radiative condi- Kentucky counties Pike, Martin, Floyd, hybrid cultivars are naturally hardier tions prevail. The flowing cold air “fills” and Letcher (eastern); Daviess, Breck- than introduced ones. As an example, lower lying areas, displacing warmer air enridge, Butler, Warren, McCracken, cold hardiness of grapevines can be clas- upwards, thus creating a temperature Caldwell, Graves, Lyon (western); Shelby, sified as follows: inversion, where temperature increases Jefferson, Spencer, Lincoln, Casey, Taylor, most hardy with altitude. Whitley, and Bell experience -15˚F events V. riparia The frequency of specified critical less than 5 percent of the time in a 30-year V. labrusca temperatures can be predicted for a period (Figure 1). Regions that experience hybrids (interspeci c crosses) proposed vineyard site on the basis of -15˚F, 5-10 percent of the time in a 30-year V. vinifera historical temperature data, the proposed period are suitable for the most tender V. rotundifolia ˚ least hardy site’s elevation, and latitude. The thresh- cultivars. Regions that experience -15 F, old at which 50 percent of the primary 10-15 percent of the time are suitable for The greater hardiness of the hybrid grape grape buds are killed (economic failure moderately cold-hardy hybrid cultivars. cultivars is the main reason they became of the crop) at maximum hardiness level The majority of the inner Bluegrass and established in the eastern United States is presented in Table 1. Hybrid cultivars the Bluegrass regions fall within this over vinifera. designation. Regions that experience ˚ A prerequisite for understanding -15 F more than 20 percent of the time minimum temperature occurrence is an Table 1. Temperature required to kill 50 in a 30-year period include Campbell understanding of the two main types of percent of the primary buds in commercially and Pendleton counties. In these coun- important wine grape cultivars in Kentucky ties only cold-hardy cultivars are recom- freezes: advective and radiative. Advec- during January (Bluegrass region). tive freezes involve the movement of an Relative mended for commercial viticulture. entire frontal system of cold air across the Coldhardiness Lethal of Cultivar Cultivar temp. (ºF) Winter Severity Index (WSI) landscape. These polar-derived cold air a Hardy Norton -22 Another limiting factor for grape masses tend to be turbulent and rapidly Chancellor -18 production is winter severity. In very moving, allowing little or no temperature GR7M -18 stratification near the ground. They are Seyval blanc -18 continental areas, such as central Eu- also termed “top-down” freezes because Vignoles -18 rope, Asia, or North America, midwinter the standard atmospheric lapse rate, or Moderately Chambourcin -15 temperatures can be cold enough to decreasing temperature with increasing hardy Chardonel -12 kill or seriously damage the grapevines. altitude, usually holds true. Both types of Traminette -12 Damage and death can occur in French- freezes can produce critical temperatures Vidal blanc -12 American and native grapevines if the Tender Cabernet -5 winter temperature falls below 5˚F. The at any time; however, radiative freezes Sauvignonb usually happen in spring and fall; advec- a Although the Norton grapevine is hardy, it WSI is the mean temperature of the cold- tive freezes are most prevalent in winter. should only be planted in regions with greater est month (January) in any given 30-year than 181 frost-free-days and greater than 4000 ˚ growing degree days to ensure proper ripening. period. If the WSI is <5 F then the winters b The commercially available clone 337 on are extremely cold (Figure 2). If the WSI is C3309 rootstock was used in tests.

2 between 5˚F and 14˚F, the winters are very Figure 1. Occurrence of -15ºF (percent of time, 1974-2005). cold; if between 14˚F and 23˚F, the winters -15˚F Occurrence are cold; and if between 23˚F and 32˚F, the <5% of the time winters are mildly cold. In western Ken- 5-10% of the time 10-15% of the time tucky, the winters can be characterized 15-20% of the time as cold to very cold. However, the regions >20% of the time around Daviess County are character- ized as having mildly cold winters (Figure 2). In central Kentucky, the winters are cold with regions of mildly cold winters occurring in and around Shelby County. The Bluegrass region is characterized as having extremely cold winters, and so is eastern Kentucky with very cold winters Kilometers occurring in southeastern Kentucky. 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East

Beginning of the Figure 2. Winter severity index (WSI) in January (1974-2005). Growing Season WSI in January Spring Frost Index (SFI) Extremely cold (<5˚F) Grapevine buds can be injured either Very cold (5-14˚F) Cold (14-23˚F) by early fall or late spring frosts. Frost, for Mildly cold (23-32˚F) the purposes of this bulletin, is described as occurring when the buds are fully -15˚F Occurrence swollen, or when the leaves are unfolded <5% of the time (Figure 3a). Spring frosts can injure some 5-10% of the time 10-15% of the time vineyards and are more frequent in some 15-20% of the time parts of the state than in others. Histori- >20% of the time cally, the Commonwealth experiences a January-thaw that reduces acclimation, followed by more seasonable damaging Kilometers low temperatures. Grape shoots are very 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East susceptible to freeze injury if tempera- tures are below 32˚F (Figure 3b). Spring frosts generally do not kill vines because Figure 3a. Swollen grape buds and unfolded Figure 3b. New shoots are susceptible to leaves are susceptible to spring frost injury. freeze injury if temperatures are below 32ºF. secondary buds will subsequently break Kilometers and their shoots will provide enough 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East leaf area to support the vine; however, secondary buds produce shoots that are less fruitful. One method of evaluating a site’s risk WSI in January of frost is based on the range between Extremely cold (<5˚F) Very cold (5-14˚F) a site’s average mean and average mini- Cold (14-23˚F) mum temperatures for a given month. Mildly cold (23-32˚F) This range is defined for spring months as a “spring frost index” (SFI) and is a measure of a site’s continentality, or tenFigure- 3.a.Figureage Swollen from 3.a. grape Swollenspring buds grape frosts. and buds unfolded April and unfoldedSFIleaves indices are leaves areFigand 3.b. NewFigwestern 3.b. shoots New areKentucky. shoots susceptible are susceptible Low to freeze frost toinjury freeze risk if injury if dency to produce large fluctuationssusceptible in susceptibleare to springshown to frost spring in injury Figure frost injury 4. SFI values less temperaturesis mostlytemperatures are found below are in32F. belowthe central 32F. region of temperature over short periods of time. than 11.0 have relatively low frost risk, Kentucky and also in western Kentucky. Bud break is influenced by air tempera- whereas those of 13.0 or greater are high Although the SFI applies to spring frost, ture, and grapevines tend to break bud risk. Eastern portions of Kentucky have the same technique is used to gauge a early if temperatures warm up quickly a high likelihood of experiencing spring site’s risk of fall frost in October. There is Kilometers in early spring. April is the month in frost events. There is moderate frost a strong correlation between spring and 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East which grape growers face the most dam- risk in northern, north-central, central, fall frost risk in Kentucky.

3 Growing Season Figure 4. Spring frost index (SFI) in April (1974-2005). Growing Degree Days (GDD) SFI Very low frost risk (<9) Grape growing regions based on Low frost risk (9-11) Growing Degree Days are presented in Moderate frost risk (11.5-13) High frost risk (>13.5) Table 2 and Figure 5. The GDD summa- tion between 1 April and 31 October is used to predict the grapevine’s ability to mature a high quality crop in the north- ern hemisphere. Vineyard suitability must adhere to baseline heat unit accu- mulation to ensure sufficient crop -ma turity. The Amerine and Winkler GDD summation divides a given area into five Kilometers regions based on the GDD summation. 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East Region I is characterized as areas accu- mulating less than 2500˚F, region II ac- cumulating between 2501˚F and 3000˚F Figure 5. Growing degree day accumulation means at 50ºF base, no upper limit (1974-2005). GDD, region III between 3001˚F to 3500˚F GDD, region IV between 3501˚F Growing Degree Days (1974-2005) ˚ Region III GDD to 4000 F GDD, and region V more Region IV than 4000˚F GDD. In Kentucky, there are Region V no areas of the state that fall within the

Region I or Region II window (Figure 5). SFI Eastern Kentucky falls into Region III Very low frost risk (<9) (Figure 5). For this region, high yields of Low frost risk (9-11) Moderate frost risk (11.5-13) standard to good quality table wines are High frost risk (>13.5) to be expected. The majority of the Blue- grass Region, southern Kentucky, and portions of western Kentucky fall into the Region IV designation. In these areas Kilometers high yield and acceptable wine quality 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East are expected with the suitable cultivars. The majority of western Kentucky falls within the Region V designation. Table 2. Grape Kilometersgrowing regions based on Growing Degree Days. 0 Growing50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East Frost-free Days (FFD) Region Degree Days Adapted cultivars and wine quality The length of the growing season I ≤2,500 Early ripening cultivars to achieve high quality (FFD), however, is more limiting to II 2,501 – 3000 Early and mid-season table wine cultivars viticulture than GDD accumulation. III 3,001 – 3,500 High yield of standard to good quality wines The FFD actually determines ecological IV 3,501 – 4000 High yield, but wine quality is only acceptable V Growing≥ 4000 Degree DaysHigh (1974-2005) production of late season wine and table cultivars for bulk pro- boundaries of sustainable viticulture. The Region III duction majority of the state has more than 180 Source: AmerineRegion and IV Winkler, 1944. FFD, which is deemed “Excellent” to grow Region V the majority of the cultivars recommend- ed for the Midwest (Figure 6). Portions of deemed “Satisfactory”. For these regions, the growing season are of special signifi- central Kentucky, however, have between early and most mid-season maturing cance. In warmer climates, ripening of 171 and 180 FFD. This corresponds to a cultivars are recommended. grapes occurs early, when the weather is “Good” designation, and indicates that still warm or even hot. These hot condi- early, mid-season, and some late-season Growing Season Mean Temperature tions cause rapid development of sugars, cultivars for the Midwest can be grown It is not yet fully understood why rapid loss of acids, and high pH levels. The successfully (Figure 6). Portions of north- cooler climates generally produce the juice is often unbalanced with respect ern Kentucky and a number of eastern best quality Kilometerstable wines, but evidence to sugar, acid, and pH, and the grapes counties have 160 to 170 FFD, which is suggests0 that50 lower100 temperatures200 duringKurtural appearand Dami, to 2006. have USDA had Viticulture insufficient Consortium-East time to

4 accumulate many chemical compounds Figure 6. Frost free days, means (1974-2005). that add distinction to the wine. A cooler Frost-free Days (1974-2005) growing season–often with considerable Satisfactory (160-170) diurnal temperature variation–slows Good (171-180) Excellent (>181) down development; better balances are achieved, and more aroma and flavor constituents are accumulated. Grow- ing season mean temperature varies considerably in Kentucky (Figure 7). The coolest, therefore the most desirable, growing season exists in isolated areas of southwestern, western, central, and south-central Kentucky. The majority of the regions in Kentucky fall within Kilometers the warm and hot growing season des- 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East ignation, especially in the central and Bluegrass regions of Kentucky. Figure 7. Growing season mean temperature from 1 April to 31 October (1974-2005).

Climate Suitability Growing Season Mean T (1 Apr to 31 Oct) Coolest and Viticultural Cool Intermediate Regions in Kentucky Warm Overall, the quality of wine produced Hot in any region comes primarily from Frost-free Days (1974-2005) the high quality of the grapes that are Satisfactory (160-170) Good (171-180) carefully vinified thorough long-held Excellent (>181) practices in the winery. The quality of the grape, however, is the result of the com- bination of climate, site, geology, choice of grape cultivar, and how these are all managed to produce the best crop. The Kilometers macroclimatic properties of the viticul- 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East tural regions in Kentucky are presented in Table 3 and Figure 8. There are five distinct growing regions in Kentucky Table 3. RankingKilometers of macroclimatic regions in Kentucky for viticulture. ranging from Region I (prime) to Region 0 50 100 Region200 I RegionKurtural II and Dami,Region 2006. III USDA VRegioniticulture IVConsortium-EastRegion V V (undesirable). Region I would lend itself Occurrence of -15ºFa <5% 5%-10% 10%-15% 15%-20% >20% to the production of premier grapes; in Winter severity indexb Mildly cold Cold Very cold Extremely Extremely Region V grape growing itself would be cold cold c a challenge. The summary of commercial Spring frost index <9 9-11 11.5-13 11.5-13 >13.5 Growing degree daysd Region III/IV Region III/IV Region IV Region IV Region V grapes suitable for planting in Kentucky Frost free Growingdayse Season Mean>181d T (1 Apr to 31 Oct)>181d 171-180d 160-170d 160-170d Coolest within these regions is presented in Table Growing season mean Coolest Cool Intermediate Warm Hot Cool 4, based on the macroclimate analysis of temperaturef Intermediate a the state. However, prospective growers Occurrence ofWarm -15ºF percent of the time between 1974-2005. b Mean temperatureHot of January between 1974-2005. Extremely cold <5ºF, Very cold 5ºF to 14ºF, Cold need to contact local county Extension 14ºF to 23ºF, Mildly cold 23ºF to 32ºF. offices for mesoclimate site analysis c Spring frost index (SFI) for April: Difference between average mean and average minimum for the month of April between 1974-2005. through the Kentucky Grape Planting d Growing degree days calculated using 50ºF base temperature between 1 April and 30 October 1974- 2005. Spatial Decision Support System before e Days between last spring frost occurrence at 32ºF and first fall frost occurrence at 32ºF between planting vineyards. 1974-2005. f Growing season mean temperature is calculated as the mean of daily maximum temperatures be- Note: This work was supported in part by the tween 1 April and 30 October 1974-2005. USDA-Viticulture Consortium East.

Kilometers 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East

5 Figure 8. Viticultural regions of Kentucky.

Kentucky Viticultural Regions Region V Region IV Region III Region II Region I

Kilometers 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East

Table 4. Summary of commercial grapes cultivars suitable for planting in Kentucky based on References macroclimatic regions. Amerine, M.A., and A.T. Winkler. 1944. Cultivar Region I Region II Region III Region IV Region V Composition and quality of musts and Vinifera None None None None None wines of California grapes. Hilgardia Hybrid reds Chambourcin Chancellor Chancellor DeChaunac Frontenac Chancellor Corot Noir DeChaunac GR-7M Leon Millot 15:493-673. Corot Noir GR-7M GR-7M Frontenac Marechal Foch Dami, I., et al. 2005. Midwest grape Noiret Noiret Frontenac Leon Millot Marquette production guide. Ohio State Exten. St. Croix Leon Millot Marechal Foch St. Croix Bull. 919-05. St. Vincent Marechal Foch Marquette St. Vincent Gladstones, J. 1992. Viticulture and the Marquette St. Croix St. Croix St. Vincent Environment. Winetitles: Adelaide, St. Vincent South Australia. 310pp. Hybrid whites Cayuga white Cayuga white Frontenac gris Frontenac gris Edelweiss Jackson, D.,Kentucky and D. Schuster. Viticultural 1987. The Regions Chardonel Frontenac gris LaCrescent LaCrescent Frontenac gris production ofRegion grapes Vand wine in cool Seyval blanc Seyval blanc LaCrosse LaCrosse LaCrescent climates. Butterworths: Wellington, Traminette Valvin Muscat Seyval blanc Seyval blanc LaCrosse Region IV Valvin Muscat Vidal blanc Vignoles New Zealand.Region III Vidal blanc Vignoles Kurtural, S.K., I.Region Dami, andII B.H. Taylor. Vignoles 2006. UtilizingRegion GIS I technologies in American reds Alden Alden Alden Alden Alden selection of suitable vineyard sites. Int. Catawba Catawba Catawba Catawba Catawba J. Fruit. Sci. 6(3) 87-107. Delaware Delaware Delaware Delaware Delaware Norton Fredonia Fredonia Fredonia Fredonia Mullins, Michael G., Alain Bouquet, and Norton Steuben Steuben Larry E. Williams. 1992. Biology of the American Niagara Niagara Niagara Niagara Niagara grapevine. Great Britain: Cambridge whites U.P., 1992. Westwood, M.N. 1993. Temperate-Zone Pomology: Physiology and Culture, Oregon: Timber P. Educational programs of Kentucky Cooperative Extension serve all people regardless of race, color, age, sex, religion, disability, or national origin. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, Wolf, T.K. 2003. Vineyard site selection. in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director of Cooperative Extension Service, University of Kentucky College of Agriculture, Lexington, and Kentucky State University, Frankfort. Copyright © 2008 Virginia Tech. Publication Number for materials developed by University of Kentucky Cooperative Extension. This publication may be reproduced in por- 463-020. tions or its entirety for educational or nonprofit purposes only. Permitted users shall give credit to the author(s) and Kilometers include this copyright notice. Publications are also available on the World Wide Web at www.ca.uky.edu. Issued 1-2008 0 50 100 200 Kurtural and Dami, 2006. USDA Viticulture Consortium-East