by Jim Law
The most frequent reoccurring debates in eastern viticulture all seem to have their roots in the quest to balance vine vigor. Issues concerning vine spacing, training systems, rootstocks or canopy management revolve around matching a given vineyard’s natural growth tendencies to its trellis space available. A balanced vine is one that fills the trellis completely, but does not require an excessive amount of hedging, lateral or leaf removal. A vineyard that cannot fill its trellis is probably uneconomical in terms of yields and will often weaken more each year unless remedial measures are taken. An excessively vigorous vineyard is expensive to manage well and often produces poor quality. After growing grapes for 17 years at Linden Vineyards I am only now beginning to get a handle on all the variables that contribute to vine vigor. My observations are not backed up by controlled scientific studies or statistical analysis, but I am out in my vineyard every growing season working with the same vines year after year. I have found the following factors (in order of importance), have the greatest impact on vine vigor.
Soil: When it comes to vine vigor, soil rules. A geological fault runs up the middle of my farm. I have many different soil types that are seemingly random in location. When I first planted my vineyard I was only slightly aware of this. I have spent much time and money retrellising and pulling out vines to accommodate the soil variations. The heavier clays are still supporting Cabernet Sauvignon vines that fill out an average of 24 feet of trellis space per vine (this is my lowest quality vineyard). Just 100 feet up the ridge are Cabernet planted at the same time that are in good balance filling 6 feet of trellis space. They are very happy on the thin shale and produce some of my best wine. This is one example of where I am learning to match soil with variety. I have been replanting my shale knolls to Cabernet Sauvignon and leaving the more vigorous sites to Merlot, Petit Verdot or Chardonnay.
I am often asked by new growers for recommendations on determining vigor potential on a new site. As we gain more experience in our region we are now able to make some educated guesses as to what kind of vine vigor to expect. Knowing soil type, depth, drainage, and organic matter content seem to be the most important variables.
Water: With the exception of my young vines, my vineyards are not irrigated. Rainfall amounts, especially in May, June and July have a big impact on vine growth. I have to manage my vineyard quite differently in a wet year, as my vines never seem to stop growing and disease pressure is high. My vines tend to err on the side of being too vigorous, so wet years are a problem and dry years a blessing.
Vine Age: When the French plant a vineyard they are thinking about what it will be like in twenty years. We seem to be focused on years 5 or 6. I have found major differences in growth habits and vigor as vines age. In some areas where I retrofitted the 5 year old vines to a divided canopy system I am now (another 12 years later) considering putting them back to a single canopy system. I refer to years 5 to 8 as the teenage years where the vines are in a growth spurt, awkward, uncoordinated and still finding their center and balance. They usually require more training and manipulation before they settle down and become adults.
Crop Load: I do believe that there is a close correlation between quantity and quality. I also see the ideal cropping level for a given vineyard as a moving target, usually dependent on the conditions of the growing season. Over the past 5 years I have been working on the affects of crop load on vine vigor. I have found it to be a good tool to balance excessively vigorous vines. I leave a very large crop on historically vigorous vines through June and July, especially in wet years and then remove the excess just before or during veraison (green harvest). I am amazed at the differences. This year in particular I had a problem with poor fruit set, but the problem was vine to vine. Some vines had a large crop, others very little. I hedge by hand, and while hedging, and looking only at the top of the canopy, I could always correctly guess the crop load of an individual vine by its vigor.
Training Systems: I have learned that one training system does not fit all situations in my vineyard. In areas where I feel there will be high vigor I use Geneva Double Curtain (GDC), medium vigor is trained to French Lyre and low vigor to Vertical Shoot Position (VSP). The downward growth habit of GDC seems to help slow down shoot growth, although lateral growth and excessive crop loads need to be thinned. Lyre is very effective in balancing growth and maintaining quality in all but extreme vigor situations, but it is very labor intensive. VSP is the easiest system to manage and produces great quality, but I have found many of my soils to be too strong for the system and the vines go into a vegetative cycle producing poor fruit and requiring too much remedial (Band-Aid) canopy management practices. When my soil balances vine growth well on VSP I can count on it to produce my best wine.
Vine Spacing (density): This is probably the one area of eastern viticulture where the experts most often agree to disagree. I have been very skeptical with the theory that close vine spacing within the rows will, because of vine to vine competition, slow down and balance individual vine vigor. However, this Spring I will be planting some vineyards at a 7″ X 4″ spacing (1,555 vine per acre) on my poorest soils to see for myself. In Europe where they have been farming for thousands of years, the soils do not have the same high natural fertility and organic matter as most of our eastern soils. In California they control water which gives them tremendous control over vine vigor. It is easier for these places to grow smaller vines and therefor plant in higher density.
Rootstock and Varietal Influences: In my experience at Linden I have seen significant vigor differences between varieties, but almost no differences between rootstocks. In 1985 I planted one acre of Cabernet Sauvignon and one acre of Chardonnay on 7 different rootstocks. I have seen no difference in vigor that I can attribute to rootstock influences. Riperia Gloire was not included in this planting, and I do look forward to future work with this rootstock. I have, however, observed significant vigor differences between own rooted and grafted Vidal.
Differences in varietal performance on different soil types can be the most important factor at Linden when deciding what to plant where. Much of this is because of vine vigor. Cabernet Sauvignon, Cabernet Franc and Sauvignon Blanc have too much natural vigor for heavier, fertile clay soils, whereas Vidal and Petit Verdot are fairly adaptable. Chardonnay, Merlot, and Seyval need good drainage, but perform well in more fertile soils with relatively high organic matter.
These are just observations from one winegrower at one vineyard. In my pursuit to grow the best wines I can from this place, I go to numerous seminars, read trade journals, and visit colleagues. Ultimately I realize that great wine can be made only if there is a certain intimacy between a grower and his or her vines. This is a very long and enriching process.