Eric Stafne, Mississippi State University
Every decision made during the establishment and life of a vineyard will be based on site selection. Considerations include:
- Elevation, including sea level and variation in elevation within the site
- Slope, or the degree of inclination of the land (% slope)
- Aspect (north, south, east, or west)
- History of the site, including previous crops/vegetation, chemicals, weeds and diseases
Elevation refers to either the elevation within a certain location (high point vs. low point) or to the absolute elevation (feet above sea level). Planting a vineyard on or near the highest point on any given location will promote better air and water drainage. Air drainage is essential in frost and freeze events. Cold air is heavier than warm air, so it settles in areas of low elevation. Water drainage is also important because standing water will limit the oxygen available to the vine root system. Even though grape vines are not particularly susceptible to damage from short-term flooding like some other fruit crops, standing water limits their growth by killing small fibrous roots that provide the majority of water and nutrient uptake from the soil.
The slope of a site refers to the degree of inclination of the land. A slight to moderate slope can be beneficial because it accelerates cold air drainage. Generally, the steeper the slope, the faster cold air moves downhill, if there are no barriers to air movement such as trees or berms. Air drainage is important for protection against spring frosts. Vegetation that slows or stops air drainage should be removed during site preparation because it can act as a dam and force cold air back up the slope.
Steep slopes can create problems. Machinery is difficult, if not dangerous, to operate on steep slopes, and the potential for soil erosion is increased. Slopes with greater than approximately 15 percent (a 15-foot drop in elevation for each 100-foot horizontal displacement) should be avoided. Consult your local Soil Conservation Service office for advice on erosion control measures.
The aspect of a slope refers to the compass direction the slope faces (north, south, east, or west). Depending on the climate of your region, different slopes should be selected for the greatest benefit of vineyard production. In cool climates where summers are cool and growing degree days are low, northern slopes should be avoided and southern slopes (S, SE and SW) are preferred to allow maximum heat accumulation on that site to grow and ripen grapes. Generally, in areas like eastern Washington and western Idaho, vineyards are sited on south/southwest facing slopes. The best wines in Germany and the other cooler regions of Europe come from south/southwest facing slopes. The key in those situations is SLOPE and windmachines for frost control.
In climates with warm or hot summers and cold winters, eastern, northern, and northeastern slopes are preferred over southern and western exposures for several reasons:
- Southern and western exposures are warmer than eastern and northern exposures.
- Southern exposures warm earlier in the spring and can slightly advance bud break, thus increasing potential for frost damage.
- Southern aspects can lead to more extensive vine warming on sunny winter days than on northern slopes. The consequences could be reduced cold resistance and subsequent cold injury. Bark splitting and trunk injury to the southwest sides of vines is occasionally observed and is related to trunk warming on sunny winter days with subsequent, rapid cooling.
- Eastern aspects have an advantage over western aspects because eastern slopes are exposed to morning sun. Vines on an eastern slope will dry (from dew or rain) sooner than those on a western slope, potentially reducing disease risk.
- In regions with warm growing and lower humidity conditions, growers may want to avoid fully west facing slopes or make changes in row orientation to reduce over-heating the fruit.
Factors such as the presence of woods, steep slopes, and exposed rocks may dictate that a less preferable aspect is used. However, management costs can be reduced if you choose the correct site for grape production rather than dealing with less-than-ideal sites.
Previous Crop History
It is important to determine the history of crop cultivation of your land prior to planting. This is critical to determine if there are any concerns with soil modifications and pests/diseases:
- Some chemicals used in agriculture and forestry have long periods of persistence in the soil and can damage new vines.
- Root rot diseases are especially a problem when certain shrubs or trees, such as oaks, were on the site prior to planting. Cleared forest sites that previously had woody plants on them should be left fallow for at least one year, and preferably three to five years to reduce the fungal inoculum in the soil. Many fungal root diseases need a host (remnant roots) to live on and can persist in the soil, thus a fallow period is warranted to prevent any problems with new plantings.
- Certain pest nematodes may cause problems in vineyards, and populations are typically higher in sandy soils. It is wise to have the soil tested for nematodes before site selection and planting.
- Excessive nitrogen in the soil needs to be identified and “grown-out” or those sites avoided.
- Aluminum toxicity can be a problem in some soils. Avoid or amend soils with low pH and/or high aluminum content. Vitis vinifera roots prefer soils of pH 6 to 7. Careful rootstock selection can alleviate the problem to a degree. Proper soil liming before planting can also alleviate the issue in the root zone. However, soil pH will have to be monitored through the life of the vineyard since acidity from untreated areas will eventually equilibrate with the treated soil, again decreasing the soil pH.
Growers must keep in mind Pierce’s disease when choosing a site, especially if they are considering planting Vitis vinifera grapes. Pierce’sdisease.org offers current news and research on Pierce’s disease.
If you intend to have a winery at the vineyard location, public access needs to be a criterion for siting the vineyard, assuming that the other conditions are reasonably met.
Cold Climate Site Selection, Cornell University
Site Selection, University of Maryland
Site Assessment, Texas A&M University
Site Selection, Virginia Tech
Site Selection, University of Kentucky
Growing Wine Grapes in Maritime Western Washington, Washington State University
Considerations & Resources for Vineyard Establishment in the Inland Pacific Northwest, Washington State University
Reviewed by Patty Skinkis, Oregon State University and Sara Spayd, North Carolina State University