Winter injury caused by low winter temperatures is an important limiting factor to grape production in many regions the United States. Our Grapevine Characteristics Chart lists grape varieties by their winter hardiness according to USDA hardiness zone. Hardiness is determined by using a number of sources, including university publications, variety release bulletins, and our own and other grower’s experiences.

A hardiness zone is a geographically-defined area in which a specific plant species (in this case, a grape cultivar) is capable of growing. The hardiness zone is defined by the average minimum temperatures of the zone (see chart on the accompanying map). Vines that are described as “hardy to Zone 7” means the vine can withstand a minimum temperature of 0°F. A more winter-hardy vine that is “hardy to Zone 6” can tolerate a minimum temperature of minus 10°F, and a vine “hardy to Zone 5” can withstand temperatures down to minus 20°F.

Most Vitis vinifera cultivars are hardy in Zones 6 or 7, meaning healthy vines can survive temperatures from zero to minus 10°F. Most American (Vitis labruscana) and hybrid varieties, including recent releases from the Cornell grape breeding program, are hardy to Zone 5 (hardy to -10°F to -20°F), and some of the newer “super hardy” cultivars developed in the Upper Midwest are hardy in Zones 3 or 4 (the hardiest of these varieties are hardy to about -40°F).

The U.S. Department of Agriculture maintains several websites related to the 2012 USDA Plant Hardiness Zone Map, which is based on average annual extreme winter temperatures from 1976 to 2005.http://planthardiness.ars.usda.gov/PHZMWeb/ allows you to locate your hardiness zone by entering your zip code.http://planthardiness.ars.usda.gov/PHZMWeb/InteractiveMap.aspx gives you access to an interactive map that shows the zones at higher resolution.

Since 1960, the USDA has released several versions of hardiness zone maps for the United States. These maps categorize locations suitable for winter survival of a rated plant in an average winter. Plant Maps maintains a website with the 1990 USDA Hardiness Zone Map that was based on data from 1974 to 1986. Interestingly, the 1990 map identified many areas as colder than did the original map issued in 1960, due to several severely cold winters in the eastern and central US during the data gathering period.

One of the drawbacks of using the USDA information is that the hardiness zones are based on average conditions, not extreme ones. Winter minimum temperatures can easily be 10°F colder in a severe winter than in an average one. For example, the 2012 USDA information considers Fredonia, NY, to be in hardiness zone 6b, meaning that the average winter minimum temperature from 1976 to 2005 was zero to -5°F. However, extreme winter minimum temperatures in Fredonia reach -15°F about once per decade. A relatively hardy vinifera cultivar such as Riesling (hardy to about -10°F) has the potential to produce a full crop of fruit in Fredonia most years, but substantial damage can occur in colder than normal winters, resulting in significant bud mortality (which will result in less than a full crop the following season) and trunk damage (which will result in the need to retrain the vines). In severely cold winters such as 1994, when temperatures dropped to -16°F with little snow cover and unprotected graft unions, Riesling vines did not survive in some plantings, and replanting of entire vineyards was necessary. Since the USDA maps refer to average conditions, and since the 1990 map is more conservative, I prefer using the 1990 information when making varietal recommendations to growers.

The USDA maps have additional limitations. Temperature variations from the average are more extreme in continental climates than in maritime regions (the extremes are more extreme). The maps do not take snow cover into consideration; snow is an excellent insulator that can protect the base of vines and roots from freeze damage. The maps also don’t take into consideration effects such as elevation. The microclimate at the bottom of a slope with little air drainage will likely be much colder on a still winter night than a site at mid-slope. Finally, the maps become less reliable west of the 100th meridian (central North and South Dakota through central Texas), since areas with low humidity have even more potential for temperature variations than those to the east.

There are many factors that influence whether or not a specific grape selection will survive and be capable of producing high quality fruit at a certain location, including winter hardiness, seasonal Growing Degree Day accumulation, length of growing season, and risk of spring frost. The USDA hardiness zone maps can be used to help determine an appropriate variety to plant in a given location keeping in mind the limitations discussed in this article.

Daily GDD = (high + low)/2 – 50

Cumulative seasonal GDD is a running total of GDD from April 1 to October 31. GDD accumulation is useful in comparing heat accumulation in one region to another or one season to another, and to predict the likelihood of ripening a crop of high quality fruit on a regular basis. GDD can also be used to predict stages of grapevine development (bud break, bloom, veraison, and harvest date), and are used in pest management programs to predict the emergence of certain insects, such as Grape Berry Moth.

A Growing Degree /Days Calculator supported by Syngenta can be found at: http://www.greencastonline.com/growing-degree-days/home. Your vineyard location can be identified by city or zip code. The default base temperature should be set to 50°F, “start” and “end” dates set to April 1 and October 31. The Calculator will indicate current seasonal GDD accumulation, GDD for any year, and, most valuably, for a 30-year average that can be used to help select appropriate cultivars to match climatic conditions.

Our Grapevine Variety Characteristic Chart lists varieties by harvest date “early”, “mid”, or “late” season based on our experience primarily in Fredonia, NY, which receives an average seasonal 2,663.5 GDD, (as indicated by the Syngenta GDD calculator). In a typical season in Fredonia, “early” harvest varieties ripen in late August to mid-September, and “mid” harvest varieties ripen in late September to mid-October. Actual harvest date might be a week or two earlier in a much warmer than average season, or a week or two later in a cooler than average season. “Late” harvest varieties typically ripen in mid to late October, although certain cultivars such as Chambourcin ripen in warmer years, and others such as Norton rarely, if ever, ripen at our location.

Just as you wouldn’t want to plant a cultivar that rarely ripens fully at your location, you may not necessarily want to grow a variety that ripens too early in the season. This is particularly true of high quality wine grape production. Grape quality is usually enhanced under cooler ripening conditions and in climates with warm, sunny days and cool nights. Grapes that ripen in hot climates or in the heat of summer often produce wine inferior to those produced in cooler climates, and dealing with fruit harvested at high temperatures can be problematic unless quick cooling of the fruit or must can be provided.

Growing Degree Day accumulation is only one measure of the characteristics of a growing season that determines whether or not a specific cultivar can be grown at a specific location. For a more complete discussion of matching vineyard site characteristics with cultivar selection, click here.

Selecting the proper rootstock for your vineyard is just as important as variety selection. Rootstocks are used to induce or reduce scion vigor or to overcome specific soil limitations caused by physical factors such as soil pH and high salt content, or biological factors such as phylloxera, nematodes, and cotton root rot. While some cultivars are commonly grown successfully on their own roots, others require the use of a specific rootstock for optimal vineyard production.

Traditionally, grapevines were grown on their own roots and, where practical, this is still a common practice. Native American varieties such as ‘Concord’ are tolerant (but not completely resistant) to root feeding by phylloxera, and with few exceptions, the ‘Concord’ industry in the Great Lakes region is comprised of thousands of acres of own-rooted vines. The main advantage of growing own-rooted vines is that vines can be renewed from new growth from buds that push at or below ground level if the trunk system is injured or killed by winter or mechanical damage. They are also easier to produce in the nursery, so initial vineyard establishment costs are lower for own-rooted vines than for grafted vines.

Until the mid-1800s, European vinifera vineyards consisted of own-rooted vines. The inadvertent introduction of phylloxera with the importation of American grape varieties changed that, and the European wine industry was nearly destroyed over the next few decades. Phylloxera is native to the eastern and southern United States. American grape varieties that evolved in the presence of phylloxera are tolerant to their feeding, meaning the vines can survive and be productive in the presence of phylloxera. Vinifera grapevines are native to Eurasia where the species evolved in the absence of phylloxera. Vinifera is susceptible (has no tolerance) to feeding by phylloxera. Once phylloxera was introduced to Europe, entire vineyards declined and died, the pest spread across the continent, and the European wine industry was decimated. T.V. Munson, a horticulturist and grape breeder from Texas, is widely credited with saving the Old World wine industry through the introduction of native Texas varieties that were tolerant to phylloxera for use as rootstocks.

While many native cultivars can be grown successfully on their own roots, vinifera and many hybrid varieties need to be grafted. According to Virginia Tech viticulturist Tony Wolfe, author of Wine Grape Production Guide for Eastern North America, “All vinifera grapes and hybrid grapes with 50% or more vinifera in their parentage should be grafted to a rootstock that provides resistance to phylloxera and nematode-transmitted viruses, such as tomato ringspot virus”. Grafted vines are produced by joining the scion variety to the variety that will provide the roots. Commonly used rootstocks – and those offered by Double A Vineyards – include 3309, 101-14, Riparia, 1103P.

3309

3309 Couderc, commonly known as 3309 or C-3309, is a hybrid of Vitis ripariaand V. rupestris, and has been the most commonly used rootstock in the Eastern US for several decades. The preeminent Cornell viticulturist, Dr. Nelson Shaulis, demonstrated that native American (Vitis Labruscana) varieties, as well as several French-American hybrids, were more productive when planted in grape replant sites when grafted to 3309 rootstock as compared to own-rooted vines. He also demonstrated that Concord grafted to 3309 was just as productive in vineyards with sod row middles and no supplemental nitrogen applications as were own-rooted Concord managed with between-row cultivation and the application of 100 lbs. actual nitrogen fertilizer annually. (http://dspace.library.cornell.edu/bitstream/1813/4946/1/FLS-045.pdf ). 3309 rootstock is cold hardy, has high tolerance to phylloxera, and produces vigorous vines on moderately acidic soils. 3309 may be susceptible to feeding by both dagger and root knot nematodes.

101-14

Like 3309, 101-14 Millaret Et De Grasset, commonly known as 101-14 or 101-14 Mgt, is also a cross between V. Riparia and V. Rupestris. On most sites, 101-14 produces a moderately vigorous vine, somewhat less vigorous than 3309. 101-14 has high tolerance to phylloxera, moderate resistance to dagger and root knot nematodes, and is a popular rootstock for clay and near neutral pH soils. The use of 101-14 rootstock has become more prevalent in recent years, particularly in Eastern US vinifera vineyards where some vigor control is desired.

Riparia

Riparia gloire, commonly referred to simply as Riparia, is a selection of Vitis riparia, a wild grape species native to the northeastern and midwestern United States. Of the rootstocks discussed in this article, vines grafted to Riparia produce the least vigorous growth. Riparia is most useful when vigor control is desired in order to produce high quality fruit on vigorous scion varieties. Because it is shallow-rooted, Riparia is less tolerant of drought, but more tolerant of waterlogged soil, than other rootstocks. It is highly resistant to phylloxera, and most sources indicate moderate resistance to feeding by root knot nematodes.

1103P

Although all of the rootstocks listed above have high phylloxera resistance and are adapted to moderately acidic to near neutral pH soils, none of them are well adapted to alkaline soils (pH above 7) or soils with high salinity, such as many soils in the southwestern United States. Vitis berlandieri, a species native to central and southwestern Texas, southeastern New Mexico, and northern Mexico, evolved in alkaline soils with high salt content. Rootstocks with V. berlandieri in their heritage are much better adapted to these conditions than are the Eastern US – derived rootstocks.

There are several commercially available rootstocks with V. berlandieri in their background, including 1103 Paulsen, commonly known as 1103P. 1103P is a highly vigorous rootstock widely adapted to many soil conditions. Unlike 3309, 101-14, and Riparia, it is well adapted to alkaline soils and those with high salt content. 1103P is highly recommended for use in areas in the southwestern US with alkaline and high salinity soils. It is a versatile rootstock used in viticulture regions around the world and is sometimes used in the eastern and Midwestern US where high vine vigor is desired or to influence mineral nutrient uptake (Effect of Rootstock on Norton Nutrient Status– Jackie L. Harris- Viticulture Research Specialist). 1103 is highly resistant to phylloxera and somewhat resistant to root knot nematodes, but has low resistance to dagger nematodes. 1103P is moderately to highly resistant to cotton root rot, a devastating soil-borne disease endemic to much of the range of Vitis berlandieri, and is considered highly resistant to Pierce’s disease, thus making it a popular rootstock choice for coastal regions and the southwestern US.

420A

420A is a Vitis riparia x V. berlandieri (the native SW US species adapted to alkaline soils and poor at taking up potassium).  For dry climates where high vine vigor is desired,1103P (berlandieri x rupestris) is often used.  420A is less commonly used and of more recent interest in areas with high rainfall (so less vigor desired) and heat, as the lower vine K uptake tends to produce lower wine must pH.  (There’s a whole side story about wine pH.  If initial pH is below 3.46 then pH tends to lower during fermentation, making it less susceptible to microbial spoilage.  If initial pH is >3.46, then wine pH tends to increase and it is more susceptible to spoilage.  Among other things.)  So 420A might be a good choice where lower vine vigor is desired AND where lower K uptake and potentially wine must pH is desired.  There’s lots of interest in VA for CF, for example, where pH can go over 4 in hot years.  In WNY and cooler regions we have the opposite problem as cooler temps produce higher acidity/lower pH (the 2 are related) fruit/wines, so 420A is likely of little value here.

A summary chart comparing characteristics of these rootstocks can be found in the Characteristics of Common Grapevine Rootstocks on our website.

Minimizing Winter Damage to Grafted Grapevines

When growing grafted grapevines in regions that receive sub-zero (Fahrenheit) temperatures, graft unions need to be covered over winter using an insulating material such as soil or mulch. This practice is discussed here-http://www.doubleavineyards.com/news.aspx?showarticle=12.

Rootstock Offerings at Double A Vineyards

Double A Vineyards offers well over one hundred grape varieties. Many of them can be successfully grown on their own roots, and we offer them only as own-rooted vines unless custom grafting is desired. We offer many hybrid varieties as own-rooted or grafted vines, and we offer many clones and varieties of vinifera grapevines only as grafted vines. While we try to anticipate grower needs by speculating and producing numerous combinations of variety, clone, and rootstock, it is impossible for us to produce every combination on speculation. We do offer custom grafting for any desired cultivar/rootstock combination, including rootstocks not discussed in this article, as long as we can source the needed plant material. If your plans include a scion/rootstock combination not listed in our catalog or on our website, please provide a minimum 18 months lead time when you order so we can provide plant material that meets your precise specifications.

Resources:

Growing Grapes in Texas– Jim Kamas

Rick Dunst, Viticulturist, Double A Vineyards, Inc. 

Now that harvest is over and winter is approaching, the staff at Double A Vineyards is starting to get a lot of phone calls and e-mails from our customers asking for assistance in selecting appropriate varieties to grow on their sites.  While many of our customers know exactly what they want, others are just getting started at growing grapes and may not know which varieties are best suited for their vineyard location.  Grape varieties differ in their tolerance to winter low temperatures; they bud out in the spring at different times, making them more or less susceptible to spring frost; and, they require a certain amount of heat units and length of growing season to fully ripen at a given location.  Knowing the limitations of your site is largely a matter of personal experience (and that of your neighbors), and our catalog and website contain a wealth of information that can help you decide on a grapevine variety suited to your site.  This article will focus on the limitations of both site and variety, and where to collect information that will help you determine the suitability of your vineyard site to produce ripe fruit from a specific grape variety.

Winter Hardiness

A variety’s lack of tolerance to low winter minimum temperatures is an obvious limiting factor to grape production in many parts of the United States.  Our catalog lists grape varieties by their winter hardiness according to USDA hardiness zone.  Most vinifera varieties are hardy in Zones 6 or 7, meaning that these varieties should be hardy to about 0° to -10°F, if they are managed well.  Native American and hybrid varieties have a much broader range of winter hardiness, with some of the newer varieties from breeding programs in Minnesota and South Dakota being hardy to an anticipated -30° to -40°F!  This hardiness information can be used along with the information provided on the USDA hardiness zone map to determine whether or not a variety may be suited to your region (more on the choice of that wording in a minute).

Our website has a link to Plant Map’s site that can determine a location’s USDA hardiness zone by postal zip code: http://www.plantmaps.com/.  While the information derived from the USDA map is useful, it has limitations.  USDA hardiness zones describe the “macroclimate”, the generally prevailing climate of a large geographic region.  However, the “microclimate” of a specific vineyard site is just as important.  For instance, the microclimate at the bottom of a slope with little air drainage will likely be much colder on a still winter night than a site at mid-slope.  When you are attempting to assign a hardiness zone to your site, make sure you have considered the microclimate at your specific location.

Spring Frost Tolerance

The likelihood of a freeze event in the spring is another consideration.  Maritime climates are influenced by large bodies of water that cool nearby land masses, thus delaying bud development in the spring.  In comparison, continental climates are subject to wider temperature fluctuations so that days are warmer and nights are colder, leading to earlier bud development and the increased likelihood of spring frost or freeze damage to the emerging buds.  There are two major factors that can influence the likelihood that a grape variety can withstand a spring cold event to produce a crop.  The most important is the time of bud development in the spring.  Some varieties inherently “break bud” later in the spring than others, thus making them less susceptible to a spring cold event.  Our Grapevine Characteristics Chart lists relative bud break information for many of our varieties (this is a work in progress and will be updated as we collect data in future growing seasons).  Varieties with differences in bud break of a few or several days can mean the difference between a crop largely lost to spring frost and a full crop of a later budding variety.

The second factor influencing successful grape production where spring frosts are likely is the ability of a variety to produce a crop, or at least part of a crop, from secondary buds that force after the primary buds have frozen.  In our experience, hybrid varieties are more likely to be capable of producing moderate crops from secondary buds than are native or vinifera varieties.

Length of the Growing Season and Growing Degree Days

In addition to knowing the likelihood that a given variety will survive winter and spring cold events, you should also make sure the variety is likely to fully ripen at your location.  Some short-season grape varieties may be able to ripen in a season as short as about 150 days (i.e., last anticipated spring frost date about May 1, and first anticipated fall frost date about September 30), while others require 180 days or more to ripen.  There are many sources of growing season information, including this NOAA site with a national map:
www.ncdc.noaa.gov/oa/climate/freezefrost/frostfreemaps.html

You can also find this information at the state and (sometimes) county level; the more detailed the information you can find for your specific locale, the more useful the information will be.

Growing Degree Days

The fourth factor in determining whether or not your climate is suitable for a specific variety is knowing the amount of heat units, or Growing Degree Days (GDD), your location receives.  The Weather Channel is an excellent source for this information:http://adstest.climate.weather.com/outlook/agriculture/growing-degree-days. GDD information is provided for a specific growing season, as well as long-term averages.

Our catalog lists each variety by time of harvest season: early, mid, or late.  Growers with shorter, cooler growing seasons will want to concentrate on early harvest season varieties, while those with warmer, longer growing seasons should focus on later harvest season varieties.  If you have questions about the suitability of a specific variety for your location, we suggest you make use of these resources, and as always, feel free to contact me at rick.dunst@doubleavineyards.com if you need further information.

A Quick Comparison of Potential Vineyard Locations

Using the information provided in this article, I determined the general characteristics of two locations where grapes are grown commercially – Hermann, Missouri, in the heart of Missouri grape country, and Fredonia, New York, in the heart of the Lake Erie Concord Grape Belt and home of Double A Vineyards, Inc.  Both locations are in Zone 5, so winter minimum temperatures may go as low as about -15°F, and the length of the growing season at each location is about 180 days.  The major difference in the two locations is that Herman, Missouri, receives an average of about 3250 GDDs per season, while Fredonia receives an average of about 2650 GDDs.  Norton (Cynthiana), Chambourcin, and Chardonel are all varieties that are hardy to at least Zone  5, and have relatively late bud break in the spring, so would be expected to thrive in both climates.  The difference is that Hermann has more than sufficient heat units to ripen these cultivars in a typical season, while the Fredonia location typically has marginal heat units to ripen Chambourcin and Chardonnel, and inadequate heat units to ripen Norton/Cythiana.  The Missouri wine industry produces some marvelous examples of Cynthiana, Chambourcin, and Chardonel wines, while growers in the Fredonia area produce many native, hybrid (and a few vinifera) varieties that are suited to the climate, but that require far fewer GDDs than are needed to fully ripen a cultivar such as Cynthiana/Norton.  Consider all the climatic characteristics of your unique location when selecting an appropriate grape variety to grow.