A Year in the Vineyard

Background Notes: Winter

March 28, 2011

The original "Winter" video is still available on Vimeo, but I suggest that you just watch the final version subtitled "The Four Seasons"
Green_Yellow_Leaves

Cabernet Franc leaves are still producing sugar for the hanging grapes on the left; yellow-leaved Chardonnay on the right has been harvested.

In Niagara the vineyards shut down quickly after harvest. The leaves yellow as soon as the vines realize that they no longer have to produce sugar to feed the grapes, as you can see with the harvested Chardonnay on the right of the picture. But the leaves valiantly remain green and produce sugar for the hanging grapes if frost stays away, as with the Cabernet Franc on the left. After the first frost the leaves fall, and the vines turn dormant. As winter approaches the shoots that bore this year's leaves and fruit turn woody or lignify.

Winter_vines

The vines in winter, with all of the growth woody or lignified.

Because fall and early winter are usually very wet, if not downright cold, little work can be done in the vineyard between harvest and winter. But some time before bud-burst, which likely occurs in May in Niagara, there is one major chore that must be completed: what we will call "winter pruning".

In both of our vineyards we are following we can identify five essential steps in the pruning process that are outlined in the video.

  • Pre-pruning: a largely mechanized process of cutting the tops of last year's shoots between the top wire and the top catching wires, to free the shoots for further pruning.
  • Initial pruning: selecting at least two of last year's shoots to become next year's canes, along with at least one or perhaps two extra shoots in case of frost or other damage.
  • Cleanup of the unwanted wood still in the trellis system.
  • Tying down of the selected shoots as next year's canes, and removing the remaining "frost canes".
  • Final cleanup and removal of the remaining unwanted wood in the trellis system.
Will_pruning_1

Will Roman pruning on March 2nd at Rosewood- still very wintry!

For Rosewood, the video showed that this process takes place in the heart of winter, with pre-pruning done in January, and initial pruning completed by the first week in March. The third step, cleanup before tying down, takes place in March and early April, while tying down will take place after mid-April, once the old shoots have become pliable enough that they can be bent and wrapped around the bottom fruiting wire of the trellis system.

The timing is dictated by the amount of work to be done and by the manpower available to complete the work, counting backwards from the expected occurrence of bud-burst in early May. Rosewood has one dedicated vineyard worker, along with our contact Will Roman who works in the vineyard on a part-time basis as he completes his schooling at Niagara college, and so the process starts very early as documented above.

Steve_pruning_1

Steve Roche pruning on March 17 at Hidden Bench - just a little more comfortable than two weeks earlier at Rosewood!

By contrast, Steve Roche at Hidden Bench had just begun the initial pruning work when we visited on March 17, but he has a crew of five experienced workers, including himself, so the initial pruning and cleanup can just be squeezed in prior to tying down. Time pressure aside, Steve says that the advantage of waiting until the weather warms is that it is easier to evaluate which of last year's shoots have survived the winter and will be the best fruiting canes.

The video gives an overview of the pruning system used in these vineyards, and in much of Niagara. It is a type of replacement cane pruning system, specifically VSP double cane flat arm, sometimes called "double Guyot".(1) This is a very labour-intensive approach to pruning that focuses on a continual replacement of the fruiting canes, and ongoing pruning to manage the growth of the vine.

Steve_pruning_2

Steve Roche is holding a shoot that is being kept as a future replacement trunk. If you enlarge the photo you can see that it is growing from the base of the old trunk.

This system keeps old wood only in the trunk of the vine, and encourages new growth to emanate from as close to the head of the trunk as possible. Old wood can be damaged by disease and by the cold, and indeed even trunks can be replaced by retraining new shoots from near the base of the trunk. In Niagara it is a common practice to foster multiple trunks, so that old, unproductive or diseased trunks can be occasionally replaced much as fruiting canes are replaced every year.

Underlying much of the work with the vines are a number of concepts related to the very nature of grape vines, that we will appeal to both implicitly and explicitly over the course of our year-long project. In order to understand the nature of vines, it's helpful to imagine them in their native forest environment. First, vines are not self-supporting. In the wild they would climb trees or rocks, any structure that would allow them to grow out of shade into the sun. And second, as a climber they are programmed to grow upwards, looking for the sun. If a vine climbs a tree, it grows up and through the tree's shade canopy, and only produces flowers and fruit from shoots that have managed to reach the sun.(2)

But slightly deeper than this is that there is a trade-off between fruit production and vegetative growth. In its natural state the vine only produces

"... enough fruit to ensure survival, and will expand its physical size to the limitations of its environment. If subject to adverse conditions, however, its natural inclination is to increase the amount of fruit it produces, usually at the expense of growth."(4)

From this background we can see some important consequences for commercial viticulture. Most obvious is that in almost all commercial environments grape vines are supported on some kind of trellis system, ranging from a simple stake to a complex set of posts and wires as we can see in our pictures and video. Second, if vines are to bear fruit for commercial purposes, they must be managed so that the areas of the vine that produce fruit have access to the sun. This is part of the goal of trellising and pruning that we will discuss in the spring and summer.

But underlying this idea is that the actual physical and vegetative growth or vigour of the vine needs to be managed and controlled. For example, in the video Will mentions that he is looking for thinner shoots with nodes closer together, and that the thicker shoots would "induce more vigour". By that he means that they would tend to generate more "bull wood", thicker shoots with a wider spacing of nodes, and more leaves. The more energy that goes into producing unnecessary vegetative growth, the less energy can find its way into producing sugar for fruit.

As Jamie Goode says by way of summary,

"So viticulturalists want to treat their vines harshly enough so that they will focus on fruit production, while giving them just enough of what they need so that they don't suffer from water or mineral deficit, which would hamper their efforts at producing ripe fruit. Thus many viticultural interventions aim at encouraging the vine to partition nutrients to the grapes so that they ripen properly, rather than concentrating on growing more leaves and stems ..."(4)

Winter pruning is the start of this process of shaping the vine to produce balanced growth and high quality and ripe fruit. Much of the work we will encounter in the spring and the summer will harken back to this principle of controlling vigour and balancing the vine's growth.

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Notes:

(1) Skelton (see reference) gives a comprehensive overview of pruning starting on p. 64, and talks specifically about cane pruning of the kind we observe here starting on page 73. He discusses the alternative approach known as spur pruning starting on page 75.

(2) Goode p. 14, Skelton p. 3 describe the vine in the wild.

(3) Skelton p. 3.

(4) Goode p. 17.

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Two useful and accessible references are:

Goode, Jamie. The Science of Wine, University of California Press, Berkeley and Los Angeles, California, 2005.

Skelton, Stephen. Viticulture, Copyright © Stephen Skelton, London, 2009.