Vineyard Site Assessment | Ed Hellman and Jim Kamas | Texas Cooperative Extension
Successful winegrape production is grounded upon a thorough understanding of the vineyard site’s characteristics. Whether you have an established vineyard, a potential vineyard site, or are seeking a suitable site, you must learn the characteristics of the site to know it’s capabilities and unique qualities, as well as it’s deficiencies. Site characteristics of overall greatest concern in Texas are: climate and weather, soil, water availability and quality, disease incidence (particularly Pierce’s Disease), and location. Site assessment should consider the sum total of all factors when evaluating the suitability for a vineyard.A critical aspect of vineyard siting is to match the site with appropriate grape varieties. The combination of site characteristics and grape varieties establishes the potential productivity, wine quality, and profitability of the vineyard. Good management practices and favorable weather enables realization of the vineyard’s potential. It is a continuous learning process to understand how grapevines interact with a vineyard site, and optimization of a vineyard’s potential requires careful application of this knowledge to planning and management practices.
Vineyard planning proceeds from one of two points of origin – either you already own land and are assessing it’s suitability for a vineyard, or you are seeking land on which to develop a vineyard. The first option is more common, but less desirable because your options are limited to the grape varieties most suited to the existing site characteristics. Therefore, if you already own the land, it is critical to assess the potential vineyard site in terms of what varieties would be best adapted to these conditions and whether these varieties fit your overall business plan. Don’t try to grow varieties that are not well-suited to the site – you will perpetually encounter greater difficulties, higher costs, and less than desired results in terms of grape quality and perhaps yield. It is much more preferable to determine which varieties you would like to grow and then find a vineyard site with characteristics that are appropriate for these varieties.
Climate and Weather
Worldwide, the average climatic conditions of a wine region determine to a large degree the grape varieties and styles of wine produced. Furthermore, wine production and quality are chiefly influenced by site-specific factors, management decisions, and short-term climate variability. Three levels of climate are recognized: the regional climate, or macroclimate, the local climate, or mesoclimate, and the climate within and between the soil and grapevine canopy, or microclimate.
The macroclimate of a region describes the broad weather and climate patterns of a relatively large area, roughly from 100 to 1000 miles or more. The mesoclimate, sometimes called the site climate, is the localized climate of a smaller area that is influenced by topographical or other landscape features. Mesoclimatic influences operate on a scale of hundreds to thousands of feet horizontally and tens of feet vertically. Mesoclimate effects are mostly related to elevation, slope, aspect, and air drainage barriers.
The microclimate of a vineyard refers to the climate from the soil upward into the vine canopy and it plays a significant role in wine quality. The canopy microclimate can be quite different from ambient conditions in the area and is influenced by management practices, particulary the training system and canopy management practices. Thus a grower can have a great influence on fruit and wine quality by optimizing the canopy climate.
Growing season temperatures are a critical aspect of site assessment because of their major influence on grape ripening and fruit quality, and therefore variety adaptation to a site. Cold temperatures are also important for their potential to cause frost and low temperature injury to grapevines.
One measure of growing season temperatures is growing degree-days or heat units. This is a rough measure of the cumulative amount of functional heat experienced by grapevines during a growing season defined as April 1 through October 31. Degree-days are determined by subtracting 50ºF from the mean daily temperature (maximum + minimum divided by 2), and calculating the cumulative sum through the growing season. The base temperature of 50ºF is used in calculations because almost no shoot growth occurs below this temperature. Degree-days can be used to compare an area’s climate with that of a known winegrowing region as a guide to selecting adapted varieties. Additional weather data should also be considered including high and low temperature extremes, relative humidity, and annual rainfall.
Spring frosts are a risk in many areas of Texas and should be considered when assessing a site. Cold air is heavier than warm air and air flows downhill, thus low spots in the local topography will tend to be colder and more frost-prone than surrounding areas. Water also will tend to pool in low spots, so for both of these reasons, avoid planting these areas. Varieties with early budbreak should be avoided in regions with high frost risk.
Low temperature injury can occur in many parts of Texas, but is a higher risk in the Panhandle, High Plains, and North Texas. Risk assessment should consider the frequency and economics of crop loss or vine damage in the business plan. Variety selection must also consider low temperature injury.
See Related Resources below for sources of Texas climatic information.
Soil characteristics are an important factor in vineyard success and must be carefully assessed when considering a potential vineyard site. Many vineyard problems are associated with one or more unfavorable soil characteristics, and it is difficult or sometimes impossible to adequately modify the unfavorable soil conditions. See our fact sheet on Vineyard Soils for more detailed information on evaluating soils for a vineyard.
Irrigation to supplement natural rainfall is a requirement for consistent, successful winegrape production in all parts of Texas. Some estimates indicate that grapevines annually require approximately 24 inches of rainfall or its equivalent in irrigation. Although there are many areas of Texas that receive more than 24 inches of rain annually, the distribution of rainfall through the season is completely unpredictable. Supplemental irrigation capability should be a critical criterion for selection of a vineyard site. Water must be available in adequate quantity when it is needed and the water must be of suitable quality for irrigation.
Water quality concerns are primarily with salinity and the amounts of dissolved salts. Existing water wells should be tested for water quality to determine their suitability for grape production. Chlorides or boron in irrigation water may accumulate in grape leaves, and water high in sodium may reduce the water permeability of soil. Salts also accumulate in soils and can reduce grape yields. See the links under Additional Resources for guidelines on interpreting water quality analysis.
The single greatest risk to growing Vitis vinifera cultivars in much of Texas is Pierce’s Disease (PD). Although the Hill Country region was once considered to be a transition zone for Pierce’s disease, it has caused losses in most area plantings and several vineyards have been completely killed by this disease. Before prospective grape growers consider any of the other economic factors crucial to financial success, it is imperative that the risk from Pierce’s disease be understood.
If the risk of PD is manageable within the proposed vineyard business plan, the site selection process can continue. Every attempt should be made to select a site with the lowest risk potential, and a grower must be prepared to follow through with timely cultural practices to manage this disease. When choosing a new vineyard site, be prepared to buy more land than will actually be planted. By creating a large (at least 150 ft.) buffer zone around vineyards, growers can either chemically or mechanically create an environment that is not favorable to insect populations. Growers should also understand that when hay fields adjacent to a vineyard are cut, large numbers of insects will be seeking alternative habitat and feeding sites. Avoid sites adjacent to creeks, streams, ponds or even depressions that retain rainwater to reduce the likelihood of consistently high leafhopper populations. Sharpshooters need water to survive and reproduce. Site development should also include removal of wild grapevines.
The occurrence and severity of other diseases are also related to climate and weather. Fungal disease pressure is much greater in areas of higher rainfall and humidity than in drier parts of the state. Significant crop losses can occur due to diseases, thus frequent spraying is required to control them, which increases production costs.
The location of the potential vineyard should be considered in terms of its proximity to winery customers and access to good roads. Availability of a local labor supply will also be important. If a winery is planned, consider the suitability of the site for a tasting room. Considerations must include marketing logistics as well as local liquor laws. Proximity to a sizable resident population or tourist traffic will be critically important for a successful tasting room. The quality of roads, ease of accessibility, and adequate parking are also important.
Related Resources on the Texas Winegrape Network
Texas Climatic Data
Irrigation Water Quality Standards and Salinity Management Strategies, Texas AgriLife Extension Service
Soil, Water & Forage Testing Laboratory, Texas AgriLife Extension Service
The Use of Soil and Water Analysis, University of California Cooperative Extension, Tulare County
Site Selection for Commercial Vineyards, Virginia Cooperative Extension