Bud break is truly a magical time in the vineyard. It occurs when grapevines that have been dormant all winter long awaken, and the new growth that will become leaves, shoots, and, most important, this year’s grapes, emerge.
The specific day that bud break occurs is dependent on the temperatures in the vineyard. Multiple days reaching fifty degrees will get the sap flowing from the roots and truck it up into to the canes (growth from the prior year). On those canes will be little bumps, called nodes. Those nodes will push out and become buds, so the prior year’s growth sets up for the next year’s crop.
Over the winter, the vineyard staff will do winter pruning and will cut back the canes. In the context of vine maturity, a cane is a mature shoot from last year’s growth that has developed a layer of bark, and no longer has leaves. The vineyard manager and winemaker do not want all the nodes on all the canes to become buds, as it would take too much energy out of the vine, and not produce the best-quality grapes. At the time of pruning, the decision is made on how many canes to leave on each vine, and how many nodes per cane. The numbers vary by vineyard manager, and is based on past experience, the specific grape and how prodigious it is, and the climate in the particular vineyard.
Now that winter pruning has been completed and the temperature has reached fifty or higher degrees many times, the sap starts flowing into the remaining canes and can be seen at the cut ends as a drop of liquid. This is called “weeping” or “crying.” Following that,, the nodes on the canes will become swollen and become known as buds. Inside that bud are all the structures for that year’s growth. There are different phases to bud development before they burst open, and when it does, it is truly spectacular. You see tiny leaves, shoots, and the flower formations that will become grape clusters.
It is during this time that the young growth is quite vulnerable to cold temperatures and frosts. If any of you have been watching the local Virginia news, as well as photos and reports coming out of Chablis, Burgundy, and other winegrowing regions around the world, you know that frosts have been hitting vineyards hard. Last year, we posted a blog about frost and frost mitigation. Late frosts in Virginia have occurred as late as Mother’s Day in past years.
Barring lost bud growth to frosts, those shoots, leaves, and flower formations will push their way out and open wide. Growth occurs rapidly at this point. Depending on the way the vineyard allows the vines to grow, the shoots may be tucked in between wires. This allows flow of air, which helps reduce molds and mildews on the clusters and warmth from the sun to help ripen the grapes over the next few months.
Let us all cheer to this magical time in the vineyard, and the birth of the next crop!