Overview
The key influences of soil composition, temperature through the various stages of the season, rainfall, wind exposure, topography and orientation all play a major role in determining the most outstanding sites for the production of high quality wine.
The ability to express the character and conditions of vineyard site in the finished wine is one of the most sought after attributes. The distinctive expression of each wine is therefore ultimately reliant on the conditions of site.
The Big Picture - Matching Site and Wine
When selecting a site for the production of any style or quality of wine, the most important starting point is to understand the goal of the finished wine. Not all sites are created equal and it is important to understand the specific idiosyncrasies of each grape variety when choosing a site upon which to grow it.
There are however universal principals that apply to the selection of a site for the production of high quality grapes, the most important ingredient in the production of top quality wine. Whilst all grape varieties follow the same cycle of growth and fruit production, there are distinct differences when you drill down further layers.
140 Year Old Barossa Valley Shiraz Vine
Variety and Site Compatibility
Varieties behave differently throughout the growing season and ripening period (typically about 100 days). Accordingly you will find variances in flowering time and growth cycle among different types of grape. These factors are key considerations in site selection, as this in turn must be able to support the ripening grape to the desired level of maturity.
Key Concerns
Frost exposure is another key concern in the selection of the right site, particularly if a cool climate is ideal for the style of wine to be made. Spring frosts are usually of the biggest concern and occur most significantly when warm weather early in the season triggers a premature or early bud burst.
New shoots and young leaves are highly prone to damage by frost or very low temperature and although secondary shoot growth can occur if the damage is early in the season, these have significantly lower crop potential than the primary shoots.
From the Ground Up
Topography can have a significant effect on the potential for frost as can wind exposure. Typically vineyards planted on valley floors in cool to cold climates are at the greatest risk of frost whilst sites on sloping terrain allow the cold air to ‘drain’ away and thereby reduce the risk of frost. Reliable air circulation through the site is another key to avoiding unnecessary frost damage and in some sites that are highly frost prone large automatically activated fans are often used to combat frost.
Composition and Rainfall
Soil composition, also referred to as soil structure, is a key consideration of selecting the correct site. Properties like pH, moisture retention, friability, depth of topsoil and mineral and nutrient availability are all of key consideration. It is important to understand that different grape varieties are compatible with different soil types and so they must be carefully matched with each other.
Rainfall is another key factor and it is important to remember that too much or too little can be detrimental to fruit quality and ultimately limit the potential of the site. Generally sites that receive significant rainfall close to or during the harvest period are unsuitable for the production of high quality wine.
Age and Orientation
It is also important to note that younger vines, particularly saplings, require more water than older vines. Irrigation is an essential aspect of viticulture in arid conditions and is particularly important in keeping the vine functioning during the fruit bearing stage of the season. Careful water management is critical to producing high quality fruit and efficient water use is essential.
Orientation in regards to the trajectory of the sun is a variable to consider for each grape variety, particularly with regard to the accumulation of tannins and phenolic compounds in the grape skins. Generally in cool climates there is desirability for greater sun exposure to achieve adequate ripeness in the fruit and in warmer climates grapes may need protection from the stronger energy of the sun.
A Case In Point - Sam Connew – Wirra Wirra Vineyards, McLaren Vale, South Australia
“Site selection is the crucial part of the whole process and basically you are looking for the coolest part in the warmest areas and vice versa in order to ensure optimum length of ripening and development of complex fruit character.
This is made all the harder in McLaren Vale because the soil can change dramatically within a few metres because it is so old. For example, the hard going clay soil – with limited top soils – will not do for whites, but will work well with vigorous varieties like Shiraz.
We also have real seasonal variation – last season was really windy and I have heard Sellicks (Wirra Wirra vineyard site) referred to as the third windiest place on earth! So you have to ask yourself, do you want your rows across or down; how will this effect the evo-transpiration rate; how is your access to water and so on…
The variables and considerations are almost endless. When considering whether or not you want north-south rows, you have to acknowledge that this will mean that one side of the row will receive morning sun, the other afternoon. On hilly sites, you need to consider whether you go down the hill – not ideal for irrigation and top soil erosion – or around the hill: better for consistency but much more expensive to do.
For example, take our Scrubby Rise plot. It is located in the McLaren Flat area with sandy loam over clay, and has a clay pan that is a little deeper than normal but still impervious – so, great Shiraz country. Rows are set east-west, thereby delivering greater uniformity in terms of sun exposure than a north-south scheme would. It is also bordered by a creek which means we have to watch the exterior rows a bit for unwanted extra vigour, but we are now monitoring this with a plant cell density map (overhead photos that chart vigour in blue and stress in red-yellow according to plant cell density).”
McLaren Vale Vineyards
Summary
Planting a vine in the ground is a business decision and should take into consideration, not only the idiosyncrasies of each grape variety but, the goal of the finished wine and the market into which this can be sold. Climatic factors such as sunlight hours, wind and rainfall all play an integral role in vine and grape quality, along with soil structure and orientation of the site, each factor influencing the finished character of a wine.