Vines produce sugar from carbon, oxygen and hydrogen. Energy is also required, and the energy comes from the sun. This process is called photosynthesis, and photosynthesis only takes place when sunlight falls on green leaves. When new shoots are growing early in the season, the vine moves most of the sugar from the leaves to the new growth where it is needed. Later, when the grapes are ripening, most of the sugar is moved from the leaves into the fruit. After harvest, the sugar is moved into the woody parts of the vine where it is stored until it is needed to start new years growth.

There is a widely held tenet that the best wines come from older vineyards. Most old vineyards have small, open canopies and produce smaller crops, so wine quality may be the result of (1) small, open canopies, (2) small crop sizes, (3) the age of the vines or (4) all three conditions may contribute to wine quality. In any case, many studies have shown that grapes grown in partial sunlight produce the best wines, and grapes grown in heavy shade produce wines having a “green” taste and poor quality.

Three general conditions can exist in vineyards. (1) Low vigor vineyards have small crops and small, open canopies. (2) High vigor vineyards have crops that are too small to balance vegetative growth, so they have large, dense canopies. (3) Medium vigor vineyards have enough crop to balance the vegetative growth, and they produce a reasonable size crop. Their canopies are large enough to ripen the crop but open enough to permit sunlight penetration and good ventilation. Medium vigor vineyards are balanced, and a good equilibrium exists between vegetative growth and fruit growth. In addition, the canopy is open and has good ventilation.

Many factors including climate, grape variety, rootstock, vine shape, soil type, irrigation, fertilizer applications, etc. contribute to vine vigor. The weight of the grapes at harvest is a measure of fruit growth, and the weight of the canes removed at pruning time is a measure vegetative growth. The weight of the fruit harvested divided by the weight of the canes removed at pruning time gives a good indication of vine balance. Establishing a balanced vineyard is not easy and several years of hard work may be required. Here are a few ways to tell if your vines are balanced.

(1) Pruning weight is about ½ pound per foot of canopy.
(2) The ratio of crop weight to pruning weight is between 5 and 10.
(3) Cane length is from 10 to 15 nodes.
(4) Node to node length is between 2.5 and 4 inches.


In overly vigorous vineyards, the canopies are too big and too dense. The sun never strikes many of the interior leaves, so they don’t contribute to photosynthesis. More importantly, the sun doesn’t strike the fruit and when grapes are grown in heavy shade, the wine often has a herbaceous taste. Most local vineyards are too vigorous. Too much water, overly fertile soils, inappropriate rootstock, etc can cause excessive vigor. Vine spacing that is inappropriately close may also produce a vine that is too vigorous for its allotted space on the trellis.

Cover Crops
Competitive cover crops can be used in vineyards to reduce soil fertility. But, the cover crop should be mowed from time to time and the clippings removed or the nutrients will go right back into the soil.

Pruning
Pruning consists of removing live canes and other vegetative parts of the vine. For new vineyards, pruning is used to establish a vine shape suitable for the type of trellis used. In mature vineyards, pruning is used primarily to establish crop size. In balanced vineyards, there will be about two clusters of grapes per bud, so the number of buds left at pruning time is an easy way to set the crop level.

Here are two general punning rules. The first rule recommends leaving 12 to 16 buds for each pound of pruning weight The second rule recommends having 4 or 5 canes per foot of canopy. Note that these two rules can conflict with each other. Here in Ramona, where most vineyard sites are excessively vigorous, the conflict between these two rules can be difficult to resolve, and getting the bud number in rule 1 into the space allotted in rule 2 is often the fundamental issue in establishing a balanced vineyard. In difficult cases, it may be necessary to change the trellis into a divided canopy or to remove vines.

Vine energy is always divided between vegetative growth, crop growth and energy stored in the wood to start next years growth. In general, vines with bigger crops will have smaller canopies and vines with smaller crops will have larger canopies. Remember that the number of buds left at pruning time determines crop size, so pruning may not be a very effective way of controlling canopy size. In Ramona, the amount of water applied to the vineyard provides a better way of controlling vine vigor.

Shoot Thinning
Vigorous vines often have canes growing from secondary buds. These canes are usually not fruitful, and they don’t contribute to the crop level. But, they cause serious shade problems in the canopy, so they should be removed. In some cases, thinning a few of the weaker primary canes should be done to help open the canopy and improve fruit quality. Keep in mind a target spacing of about 3 inches between shoots. Cane thinning should be done well before or after bloom because removing too many canes during the flowering period can reduce fruit set.

Leaf Pulling
Many growers rely on leaf pulling to improve wine quality. The leaf at the cluster and the leaves just above and below the cluster are removed to permit more sunlight on the fruit. More sunlight increases “red fruit” tastes in the wine and reduces green, herbaceous tastes. In addition, better ventilation and improved spray penetration results in better mildew control. But, leaf pulling should be considered a temporary remedy. Changing the growing conditions or modifying the trellis system to open the canopy are better long-term solutions.


Low vigor vineyards have small, open canopies. Both the fruit and leaves have good sun exposure, so low vigor vineyards may produce good quality wine. But, the crop size is often too small to make the vineyard economically feasible. Balancing low vigor vineyards may be easy or difficult depending on the problem. Low vigor vineyards can be easily balanced when low vigor results from too little water or from poor nutrition. Here, just changing the irrigation schedule or applying an appropriate fertilizer will often solve the problem. On the other hand, a vineyard with poor soil conditions may be very difficult to balance without extensive groundwork or even replanting the whole vineyard. Fortunately, many low vigor vineyard sit es are easy to balance.

Pruning
The number of buds left at pruning time determines crop size. But, heavy pruning to reduce crop size also reduces the number canes and the number of leaves on the vine. Since sugar is made in leaves, pruning may not be the optimum way of controlling crop size in low vigor vineyards.

Crop thinning
Removing flowers just before bloom or removing clusters shortly after fruit set is called thinning. When combined with lighter pruning, thinning can reduce crop size without reducing the leaf area of the vine. Then, more energy can be produced and concentrated into a smaller crop. Vine vigor is controlled, and wine quality is improved. Removing flowers before or soon after bloom produces the best results because the vine can concentrate its energy into the remaining fruit throughout most of the growing season.