General climatic conditions in many sections of the Midwest are favorable for growing grapes. Most American and French hybrid grapes can be grown where the frost-free period is from 150 to 180 days. The longest frost-free growing seasons in the region are found along the shores and islands of the Great Lakes and in the southern areas bordering the Ohio River Valley.
Information presented in climatological charts is general, so specific sites that have more or less desirable conditions can be found within any general area. Sites should be evaluated individually, and cultivars should be selected according to the length of the site’s growing season and the expected minimum winter temperatures.
If the growing season is too short for a particular cultivar, fruit may not mature completely and may be poor in quality and low in sugar content at harvest. In addition, the vines may not mature properly in the fall, leading to possible winter injury. If the cultivar is not hardy enough to survive the winter, vine performance would be unsatisfactory.
Vineyard disease problems may be related in part to climate, especially humidity and temperature. Diseases such as black rot and downy mildew are more frequent under warmer temperatures and high humidity than in cooler, drier areas. Consequently, disease-control programs may need altering from one climatic region to another, as from northern to southern parts of the region.
The Concord cultivar is generally one of the most cold-hardy grapes commercially grown in the Midwestern United States. Other cultivars often are damaged more than Concord in any particular season. Some of the other cultivars commonly produced commercially are significantly less winter hardy than Concord. A relative rating of winter hardiness for the various cultivars is provided in the section on Cultivar Selection beginning on page 18.
Vines begin to acclimate or harden off to cold temperatures as they go dormant in the fall. Early in the winter months, vines may not have achieved adequate hardiness to withstand temperatures below 0°F. However, by the first week of January, vines have usually achieved maximum winter hardiness and may be able to withstand temperatures as low as -10°F to -30°F, depending on the cultivar. Consequently, the extent of cold damage that may occur is dependent on the time of the year and the level of cold (Figure 5).
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| FIGURE 5. Riesling vine with top killed by -22ºF temperature with regrowth from the base. |
In addition, the pre-freeze conditions can also affect the amount of damage that occurs. This is especially true if there are warm periods (January thaws) followed by rapid drops in temperature. In many years, it is not the mid-winter cold that is responsible for cold injury but the fluctuating temperatures that occur in late winter.
By late winter, the rest requirement of the vine also has usually been achieved. After the winter rest period is completed, the vine is ready to grow, and only cold temperature keeps it dormant. Any significant warming can cause the vine to deacclimate (lose cold hardiness). If subsequent cold temperatures occur, vines frequently difficult to determine exactly when or how a vine was damaged unless it is periodically examined throughout the winter.
Once growth starts in the spring and the buds have extended to approximately 2 inches in length, they are susceptible to damage from temperatures below 28°F. Temperature variations caused by mesoclimates within a vineyard usually exist; temperatures usually are lowest near the ground, and they increase with elevation. Therefore, when possible, growers should establish vines on a trellis and grow them at a height of 5-1/2 to 6 feet.
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| FIGURE 6. Bud cross section showing dead primary (dark tissue in the center), but live secondary and tertiary buds on either side. |
Once primary buds are dead or damaged, various effects will result, depending on the variety (Figure 6). Although secondary buds generally will produce fruit, the crop will be significantly reduced. This subject is discussed further under Selection of Cultivars, Pruning and Training, and Cultural Practices That Aid in Disease and Insect Control.
Selection of a site with desirable climatological characteristics helps to reduce cultural problems and assure success of the vineyard. The best vineyard sites are those with full sunlight, freedom from frost injury, and good soil drainage.
The most frost-free sites are those higher than the surrounding areas. Cold air drains from higher sites into lower areas. Avoid low areas where cold air may settle, because injury is likely to be greater and yields are likely to be lower where low-temperature injury occurs. Sites south and east of the Great Lakes often provide favorable temperature conditions in both spring and fall. Even in these locations, vineyards on higher elevations are less subject to frost damage than those in low areas.
Generally, sites with steep slopes (15% or more) should be avoided in commercial plantings because of soil erosion and difficulty in operating vineyard equipment. Cool temperatures on northern slopes often delay vine growth enough in the spring to aid in avoiding frost damage. However, these slopes may be subject to harsher winter conditions.
The opposite effect may occur on a southern slope, resulting in earlier spring growth and increased risk of frost injury. A western slope may have the disadvantage of exposure to prevailing winds that, in some areas or seasons, could be strong enough to damage vines and cause special trellising problems. On the other hand, movement of prevailing winds through a vineyard helps dry dew and rain from the foliage and helps reduce disease problems.
Monitoring or mapping of site conditions before planting is very desirable. Any prior knowledge of an area’s elevation effects and other conditions may help producers locate their vineyard above certain critical levels and avoid damaging seasonal frosts. Advice from those who have grown fruit trees or vines in a given area can help potential producers find the elevation or location of the thermobelt and thus avoid undesirable areas.
Grapes can be grown on a variety of soil types. However, the highest vine vigor and yield and the most efficient production are achieved on soils with good internal drainage. Water drainage means surface removal of water as well as percolation or internal movement of water. With good management, vineyards have produced satisfactorily on soils ranging from gravelly loams to heavy clay and silt clay loams.
Producers should avoid soils that are consistently wet during the growing season (Figure 7). These soils may have an impervious subsoil or other drainage problems. In poorly drained soil, roots may penetrate only 2 feet or less, whereas on a deep, well-drained soil, they will penetrate 6 feet or more. Soils with only fair drainage require more intensive soil management (e.g., tiling), and yields may not be satisfactory (Figure 8).
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| FIGURE 7. Poor drainage with standing water should be avoided. | FIGURE 8. Equipment used to install drain tile between rows in a vineyard with imperfect soil drainage. Photos courtesy of Gene Sigel. | ||
Just as cold air should not be allowed to stagnate on a vineyard site, neither should water be allowed to accumulate. The vineyard must be arranged so that no ponding or puddling of water will occur for extended periods following a rain. This is especially crucial during the growing season.
Subsoil characteristics are important when choosing a vineyard site because they often indicate the nature of internal drainage. For example, a bright, uniformly yellowish-brown subsoil indicates good internal drainage. Subsoils showing slight mottling of yellow, gray, and orange indicate only moderate drainage. Poorly drained subsoils are characterized by greater mottling or, in some cases, a uniform dark-gray color.
The USDA Natural Resources Conservation Service (NRCS) has mapped most of the soils in the Midwest. Before producers establish a planting, they should contact the local NRCS office to obtain county soil surveys and examine the soil conditions in the proposed vineyard site. Soil maps are helpful in determining soil-drainage characteristics and in evaluating potential sites. However, maps are not substitutes for taking soil borings on the site and making visual evaluations of the subsoil.
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| FIGURE 9. Example of soil profile with adequate drainage. |
Internal water drainage is extremely important, especially for the more cold-tender French hybrid or vinifera grapes. A soil profile, as shown in Figure 9, can allow water to move freely through it. However, many Midwestern soils have fragipans, impermeable layers or texture changes that prevent free downward movement of water following rain or irrigation.
Lateral movement of water at a given depth below the surface can result in overly wet conditions, harming the vines. Therefore, even a sloped vineyard can have problems with internal drainage. Operating equipment in wet vineyards in early spring or late fall can also cause compaction and create serious problems.
Producers should note that general soils and topographic maps that give the major soil types and conditions for an area are not sufficient to determine the best location for the vineyard.
Specific sites for small acreage may be found that are considerably more favorable than the general map would indicate. Therefore, potential growers should not be discouraged based upon this general information, but should request detailed topographic and soils maps from their local NRCS office. These maps provide more information on the conditions for a specific site.
If the general topography (elevation, slope, etc.) is favorable but the internal drainage is imperfect, tile drains should be considered. Tile drainage generally improves most sites for the production of grapes and other fruit crops. Producers should carefully examine these conditions before the vineyard is planted.
Although grapevines grow and produce best on fertile, well-drained soils, naturally high fertility is not essential. Through proper fertilizer applications and soil management practices, even low-fertility soils can be improved to grow high yields of quality fruit. Thus, drainage considerations usually are more important than soil fertility when selecting a vineyard site. Improving soil fertility generally is more economical than compensating for poor water and air drainage on the site.
Because erosion is a major concern, most vineyard rows should be planted perpendicular to the predominant slope. Row directions running up and down slopes should be avoided. Contour plantings should also be avoided as they may introduce cultural or management problems and may result in weaker trellising.