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01/01/2011

Pruning for Quality

Like fruit trees and rose bushes, grapevines need to be pruned every year to keep them healthy and productive. In fact pruning – which essentially eliminates all or nearly all of the vine growth (called canes) from the previous year -- is one of the most important and intricate tasks California wine grape growers perform all year.

“Pruning sets the stage for the entire growing season,” says J.D. Harkey, director of operations and field supervisor for Drake Enterprises, which farms 500 acres of wine grapes in the Temecula Valley AVA. “It’s a key practice in determining vine balance and what the vines will produce in the coming year in terms of both quality and yield.”

Grapevines are pruned in the winter when they’re dormant generally somewhere between leaf drop in the fall and budbreak in the spring depending on the weather and the vines’ susceptibility of frost damage. Growers wait until all the leaves have fallen off (usually after there’s been a good cold spell), and they also look for brittle canes as a sign that the vines are completely dormant. Sometimes they’ll even make a test cut to make sure the cut wound heals quickly.

When the vines are ready for pruning, wine grape growers need to consider a number of factors having to do with the yield and quality they’re looking for. First and foremost they want to create a vine that has enough buds to produce the size of crop they want in the coming year. The more buds left on the vine, the more fruit the vine will produce. Although it might seem natural to leave as many buds as possible (to produce a lot of fruit!), wine grape growers are careful to modify the vines’ vigor because less fruit per vine can make the resulting wines more concentrated and intense. Growers are also mindful of spacing out the buds along the vine so that when new growth comes in the fruit will be exposed to sunlight and the canopy will have good air circulation – factors important to the ultimate quality of the grapes.

There are three basic types of pruning depending on what type of trellising system is in place and what the grower wants to achieve. The most common is called spur or sometimes cordon pruning, a method often used with medium to high vigor grape varieties such as Cabernet Sauvignon, Merlot, Sauvignon Blanc and Syrah. With spur pruning the dormant canes that grew from the vine’s “arm” or “cordon” the previous year are cut down to “spurs” that each contain two or three dormant buds. Each bud will produce one cane, and each cane will produce two clusters, so pruning in this way allows the grower to accurately control the fruit yield per vine.

Another relatively common but more labor-intensive method of pruning is called cane pruning, used most frequently with low vigor varieties such as Pinot Noir. With this method two healthy canes from the previous year are selected – the rest are cut off – and carefully wound around and tied to the trellis wire extending in opposite directions from the vine trunk. Cane pruning ensures that the growing shoots will be evenly spaced in the spring; it also allows sunlight into the canopy when a vertical trellis is used, and some growers like it because the fruit grows from new wood every year.

The third and least common method of pruning is called head-training, and it’s reserved for vines that have no trellis system. Many of the old Zinfandel vines around California are head-trained; they look like beautiful stunted trees. But head training is challenging – the key is to leave enough buds to produce a crop, but to try to spread them out throughout the vine “arms” so that the canopy doesn’t get lopsided and threaten to topple the vine.

No matter what method is employed, growers agree that it takes a special kind of expertise to properly prune a grapevine. Although some “pre-pruning” can be done with a machine attached to a tractor (only when the vines are spur pruned, however), it takes a person to come back through and make the final cuts, ensuring that just the right amount of buds – and the healthiest canes and shoots – are left on the vines.

“Pruning is an art, no doubt about it,” says Harkey, who notes that vineyard workers spend years learning – and passing down – proper pruning techniques. “It’s a part of wine grape growing that will always require the human touch.”

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Dormant vines await an important winter task – pruning.

 

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