There's an old aphorism (French, I think) that the vines must suffer in order to produce good wine. While this isn't exactly true, its origins are easy to understand. I''ll try to explain the basis for this belief and how that is connected to soils, irrigation, fertilization, diseases and yields.
Grapevines are very vigorous plants, not only capable of surviving in poor soils, but often thriving in soils that are unsuitable for most annual food crops. Vines are very efficient at using water and scavenging nitrogen from the soil, and can grow too vigorously if they have an abundant supply of either or both. You might ask why would high vigor be a problem when most farmers are thrilled to have bigger, healthier plants. Overly vigorous vines not only produce lower quality wine, they also produce smaller crops – a lose/lose proposition.
The reasons for smaller crops are two fold: low bud fruitfulness and poor set. Grapes are borne on shoots sprouting from the previous year's canes, and the potential crop is determined when those buds are being formed. Moderate temperatures and direct sunlight (red and infra-red wavelengths) are critical to the formation of grape cluster primordia in these buds. Cool rainy springtime weather can result in significant crop reduction the following year due to reduced cluster count and smaller clusters. There are people who perform microscopic analysis of buds in an attempt to determine how many buds to leave at pruning time. Poor set is often caused by bad weather at bloom time but can also be the result of internal factors such as nutrient or water deficiency, and also excessive vigor. The teleological explanation of the latter is that if growing conditions are so good, why should the plant bother making seeds. High vigor and low fruitfulness can become a self-perpetuating, vicious circle: vines with less fruit grow more leaves, creating more shade, reducing fruit production, increasing leaf growth, etc.
While wine and grape quality is subjective, most of the effects of excess vigor have universally accepted negative impact on wine quality. The most obvious is dilution of flavor due to larger berry size. Because color and flavor are concentrated in the skin of the grape, the lower skin : pulp ratio of larger berries means less color, aroma and flavor (everything else taken equally). Another effect of vigor is decreased light , both direct and indirect, on the clusters, delaying flavor and color development. A light bulb went on in my head during a 1983 trip to Burgundy and Bordeaux when I saw how the vines were trellised there. I had always wondered why California wines were generally more “green” and herbaceous at higher ripeness levels (in terms of sugar and acid) than their French counterparts. The shoots in the French vineyards were trained into a thin hedge, and the fruit was visible at the bottom of the hedge. At the time, virtually all California vineyards were pruned on a “fruiting wire” with a 24” crossarm mounted a foot higher with foliage support wires at each end. The shoots grew up and out, over the foliage wires and down, no manual labor required. This exposed a large leaf area to the sun, allowing the vines to produce plenty of sugar, but created a tunnel around the grapes with little light penetration. I can remember driving past vineyards a week before harvest and not being able to tell what color the grapes were. In addition to retarding color and flavor development, this system reduced fruitfulness and increased disease problems.
In the mid to late 1980s some growers started changing to a vertical training system. Sunlight Into Wine by Dr. Richard Smart, published in 1991, became required reading for growers and vineyard managers. A large amount of replanting due to Phylloxera that had spread during the late 80s hastened the change. This also led to a dramatic increase in the year-round vineyard labor force. Whereas the old system required hand labor only for pruning, harvest and maybe some suckering, the new system involved placing and moving foliage wires, tucking shoots between the wires, leaf removal and additional suckering, creating work all Spring and Summer. During the replanting many growers also chose rootstocks with lower vigor than the AxR they were replacing.
Now let's look at the factors that limit vigor, or make the vines “suffer”. Choice of location, specifically soil, is the oldest and most obvious. In Europe olive trees and grapevines were grown on low fertility soils with the double benefits of higher quality fruit and not tying up more fertile land needed for cereal grains and other annual crops. Water retention is probably more important than soil nutrient status, but both influence vigor. Without drought stress vines will not only grow excessively, they also will not concentrate sugar any higher than about 20% in the grapes (11-12% potential alcohol). Most of the wine growing regions of France receive significant rain during the growing season (April-September) and have proscriptions against irrigation. This has led to a fairly widely held belief that dry-farmed vines always make the best wine. I would argue that although excess water is deleterious to quality, so is insufficient water. We have 8+ acres of old dry-farmed vines that suffer too much in drier years and would make better wine those years if we could give them a bit of water. Likewise, wine quality in a number of regions of France suffered during the extremely hot and dry 2003 vintage. Vines don't care whether their water comes from a cloud or a drip hose; they do need some water.
As an aside, when I was in Paris in 2007 I found an interesting little wine shop in our neighborhood. When the proprietress found out I was a California vigneron she started telling me all of the California vineyard shortcomings. I highly doubt she had ever even been to the US, but she proceeded to tell me the soils were all the same, the climate was too hot, the vines too young, the vineyards too big and, worst of all, that we irrigate. With my limited French I argued every point: We have some of the most diverse soils in the world, being at the juncture of two huge tectonic plates. San Francisco is colder than Normandy in the summer and you could never ripen a grape there. I have unirrigated vines over 100 years old. My vineyard is only 8 hectares (she responded that some of her growers farmed only 4 or 5 hectares). Lastly, I told her that we don't get any rain during the season, and vines don't care where the water comes from. I'm not sure I caused her to have any doubt of her opinions of California, but she really took offense at that last suggestion. All in all it was an amiable “argument” and I did respect her support of artisan producers – she had wines that were both interesting and good.
Back in the early '90s my friend Organic Bob (the one who tried to get me to buy a propane weed flamer) extolled the virtues of grapes from phylloxera infested vineyards, his theory being that the increased vine stress improved quality. As strange as it seems, there is some, limited, truth to this. In situations of excess vigor, disease can actually bring the vine into better balance. Unfortunately, phylloxera doesn't just weaken vines a little, it ultimately kills them. While one vineyard with which Bob had experience may have made better wine one year, that was the exception rather than the rule. Most phylloxerated vineyards fail to ripen grapes well; I remember one winery marketing a rosé (that was supposed to have been a red wine) called Bug Juice one year. I believe that mild grape leafroll virus (found in quite a few old vineyards) can sometimes have a beneficial effect on wine quality by slowing sugar production and accumulation. These disease or pest problems can only have a quality enhancing effect if the vineyard is otherwise overly vigorous. It is the goal of any good vineyard manager to have a healthy, balanced, fruitful, high quality vineyard.
I know quite a few winemakers (but not grower/winemakers) who claim the lower the yield, the higher the quality. The flawed logic is that if 6 tons per acre (TPA) makes better wine than 9 TPA and 4TPA better than 6TPA (usually true), then 2 TPA will be better than 4, 1 TPA even better...The sins of overcropping are well known, and most growers want to grow as large a crop as they can ripen properly. However, too small a crop can actually harm quality; the vines are out of balance, grow too vigorously, compensate by increasing berry size (diluting flavor and color) and ripen grapes too quickly.
In summary, excessive vine vigor is a lot more common than insufficient vigor, but the best wines come from balanced vines, not suffering vines. Soil and climate are set factors that have huge influence on vine vigor, but growers can adjust and attain balanced vines through informed use of rootstock, spacing, trellising, pruning, fertilization and irrigation. A well designed vineyard needs less intervention to attain balance, is easier and cheaper to farm, and will be more consistent in producing high quality wine. What constitutes a well designed vineyard? It's a vineyard that has a compatible combination of site, rootstock and scion variety, and spacing and trellising that produces a good balance of fruit and foliar growth. It is not so vigorous that a lot of leaf removal or other remedial canopy work is necessary. It is not so low in vigor that it needs lots of fertilizer or irrigation. It's a vineyard that usually sets enough crop but doesn't need a lot of thinning. A good vineyard also has uniformity. Many vineyards have variable soil depth and composition; this results in uneven vigor if the site is farmed in uniform fashion. One year one of my growers wanted to irrigate his whole vineyard late in the season because a few weak vines were losing a lot of leaves. 80 % of the vines were fine, 15% too vigorous and 5% suffering. I told him you can't farm based on the weakest 5% of your vineyard – there's too big a compromise of quality. The next year he put in extra emitters for the weak vines and also (hooray) valves to cut off water to the overly vigorous areas, which are now virtually dry farmed.. A well designed and managed vineyard compensates for soil variation with different rootstocks, different spacing and variable irrigation.