Why Does Vineyard Site Location Matter?

At Philip Carter we have three vineyards; Bigfoot in Warrenton, Philip Carter Winery (PCW) in Hume, and Strother Family Vineyard (SFV) in Delaplane.   Each is situated at a unique location.  While you are all familiar with the vineyard at PCW, the strongest vineyard that we have is our youngest, SFV.  It exemplifies some aspects of site location that I am about to go over.  When you see Tony or me in the Tasting Room, feel free to ask us about this great site and what exciting developments it is bringing to Philip Carter Winery.

Let me preface this by saying that site location is a complex topic with myriad factors going in to having the right location for a vineyard, but in a perfect world, we would take all of these elements into account when selecting a site.  Vineyard site selection is probably the most important decision in the life of a vineyard. It takes several years to develop a vineyard and produce a regular crop of grapes.  A vineyard will remain productive for decades.  Although grapevines can grow in many places, successful cultivation for quality wine production is limited to sites where specific conditions are met and rigorous management practices conducted. Some of the primary factors affecting vines are as follows:

• Physical Environment (e.g., elevation, latitude, slope, aspect, soil type);
• Natural Phenomena (e.g., climate, seasonal variations, weather & hazards);
• Viticulture and Vineyard Management (e.g., layout of vineyard, grape varieties and rootstocks, infrastructure (irrigation, wind machines)).

This is a lengthy topic and for today’s conversation I am going to address some of the physical aspects that you must evaluate when selecting a vineyard site.  Be warned, that this discussion is going to get a little technical.

Elevation

Elevation influences the minimum and maximum temperatures in a vineyard. Lower elevations are preferable at high latitudes, and higher elevations are more desirable at lower latitudes. On average, the temperature falls 1.1 degrees F per 330 feet (0.61°C/100 m) of elevation, which means the growing season will be shorter increasing the possibility of frost at higher elevations.

Relative Elevation

Poor relative elevation can significantly reduce the quality of an otherwise good site; such is the case with vineyards located within valleys.  Although the vineyard may fall within the acceptable absolute elevation range, because of its location at the lowest point at an otherwise good elevation, it may be prone to spring and fall frosts.  It is better if the vineyard is located at an elevation referred to as the “thermal belt.” The thermal belt is a mountainside zone where frost or freezing temperatures are less likely to occur than they are at either higher or lower elevations.

Latitude

Grapevines are temperate-climate plants; the major viticulture regions of the world are concentrated between the latitudes of 30 and 50 degrees.  In this zone the relatively large diurnal (daytime vs. nighttime) temperature range is optimal to produce the combination of sugar and acid levels that enable grapes to be made into quality wine.

Slope

The slope of a site refers to the degree of inclination of the land expressed as a percentage.  For example, a 5-foot fall over a 100-foot horizontal distance would be a 5 percent slope. The ideal site for grapevines is on gently sloping land that allows cold air to drain into lower areas.  This reduces the risk of frost injury and cold winter temperatures.  Further, good air drainage promotes faster drying canopies, which reduces the frequency of disease.

Aspect

A vineyard’s aspect refers to the direction that the slope faces (e.g., east, southeast, etc.). Aspect affects the angle that the sunlight hits the vineyard and heat balance.  Aspect is more important in higher latitudes where radiation is weaker, due to the angle of the sun, and light interception may be limiting to growth.

• Southern-facing Aspects

Vineyards with southern aspects (for the Northern Hemisphere) warm earlier in the spring and the vines may undergo bud break earlier than vineyards with northern aspects. The early bud break is desirable in locations that do not have a danger of spring frost because it translates into earlier bloom and harvest of the fruit.

• Western-facing Aspects

Western-facing slopes are a popular choice for late-maturing varieties, such as Cabernet Sauvignon, promoting fruit ripening in the waning heat and daylight of fall.

• Eastern-facing Aspects

Eastern-facing aspects receive the first of the morning radiation, warming canopy and soil temperatures fastest when temperatures are generally at their lowest and most limiting.

• Northern-facing Aspects

In cool climates where summers are cool and growing degree-days are low, northern slopes (for the Northern Hemisphere) should be avoided and southern aspects (S, SE, and SW) are preferred to allow maximum heat accumulation on that site to grow and ripen grapes.

Soil

Soil supports vine root structure and influences the amount of minerals and nutrients available to the vine.  The ideal soil condition is a layer of thin topsoil and subsoil that retains water but also has good drainage so that the roots do not become overly saturated.  The ability of the soil to retain heat and/or reflect it back up to the vine is also an important consideration that affects the ripening of the grapes.  Some of the more common soils that we see in Virginia are as follows:

• Clay

Sedimentary rock based soil that has good water retention ability but poor drainage. The soil is often very cool and high in acidity. The Right Bank of Bordeaux is dominated by clay-based soils.

• Granite

Composed of 40-60% quartz, 30-40% Orthoclase and various amounts of hornblende, mica, and other minerals. This soil warms quickly and retains heat well. The soil’s high level of acidity works to minimize the acid levels in the grapes.

• Loam

Warm, soft, fertile soil composed of roughly equal amounts of silt, sand and clay. It is typically too fertile for high quality wines that need to limit yields in order to concentrate flavors.

• Shale

Fine grain sedimentary based soil that can turn into slate when under pressure. The soil is moderately fertile and retains heat well.

I have just hit you with some very technical information, my suggestion is that the next time you are at a winery with an attendant vineyard, take some of these factors into account and evaluate the site.  Then ask questions during your tasting or with knowledgeable members of the winery staff.  You will learn more and it can be fun for the staff to have an in-depth conversation.   Personally, I love to geek about wine and have great conversations with others who are interested in our industry.