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03/01/2011

New Beginnings: Budbreak and Planting

Like a gardener itching to get outside as soon as winter finally peters out, California’s wine grape growers can’t wait to get back in the vineyards at the first sign of spring. In the Golden State, that usually happens sometime in March, when the ground temperature gradually warms and heat begins to penetrate several inches into the soil. When the temperature reaches 50° degrees Fahrenheit at about a foot underground, the dormant vines come to life.

The first outward sign of this awakening is known as “weeping” or “bleeding.” “As the soils warm up the vine roots absorb water and nutrients which are pushed up through the vine and excreted as sap at the tips of the spurs and canes that were pruned over the winter,” explains Jason Smith, owner and general manager of Paraiso Vineyards in Monterey County. Depending on the conditions, a vine can expel over a gallon of water during this weeping period.

This liquid excretion is a sign that the vines are preparing themselves for “budbreak,” when tiny buds on the vine enlarge and eventually open. Dormant buds are covered by many layers of bud scales that protect them during the cold weather. As temperatures rise, the buds swell and ultimately break through the scales; soon after that, shoots begin to grow from the buds, sprouting tiny leaves that kick off the process of photosynthesis and accelerate growth.

The timing of budbreak is an important clue as to how the growing season will play itself out. “An early budbreak can mean an accelerated growing season, when every stage of growth occurs a week or two earlier than usual,” says Smith. “It affects how we plan all of our activities in the vineyard, from frost protection to leaf pulling and crop thinning to harvest.” Of course it’s hard to make hard and fast predictions where Mother Nature is involved. Cool weather in the summer and early fall can slow growth and grape cluster development, returning what appeared to be an early growing season to its “normal” pace.

Spring is also the time when wine grape growers plant or replant their vineyards, if necessary. A healthy vineyard can be productive for 25-30 years (and some “old vines” can live to be over 100 years old!), but sometimes diseases can cut the life of a vineyard (or block within a vineyard) short, or a grower may decide to replace one variety with another that he or she thinks will grow better in that spot.

There are dozens of decisions that go into planting or replanting a vineyard, including site, climate, soil, variety, clone, rootstock, vine orientation, trellising, etc. “Deciding what, where and how to plant involves many variables,” says Smith. “Matching the soil types and specific microclimate to each variety you plant and determining the best way to orient, space and train your vines is crucial to growing high quality wine grapes.” Indeed, because California has so many types of soils and microclimates, many growers divide their vineyards into small blocks, planting different clones, rootstocks and even varieties in each one according to its particular characteristics.

When all the upfront decisions have been made and the soil has been prepared (deep ripped to help mix the soils where they need it) and amended with nutrients, growers carefully lay out the vineyard rows, determining how much space will be left between the rows and between each vine. Most growers in California plant either rootstock -- a root used to establish a grapevine that will be propagated through grafting the following fall or spring -- or benchgrafts -- grapevines which have already been grafted to a root system. “Own-rooted” grapevines -- grapevines that grow on their own roots – are rarely used because of their susceptibility to disease. Whichever planting material growers use, it’s important to get the planting done in March or April so that the vines have access to enough water to establish strong root systems. During the first few months, it’s also common to place a tube (or sometimes a milk carton) around the young plant to protect it from hungry rodents and/or birds.

Finally, spring in California’s vineyards is also the time when cover crops – crops planted between the rows in the fall – come to life. Cover crops have many benefits, including controlling erosion, building organic matter and suppressing weeds, and they also make a good home for beneficial insects and spiders, which growers monitor carefully starting in the spring. “Just as the vines are awakening from their dormant stage, so are the bugs – both the good ones and the not-so-good ones,” says Smith. “As growers, we keep our eyes on all of them.”

Photo courtesy of Mora Cronin.

The timing of budbreak gives winegrape growers an inside look at how the rest of the season will play out.