The Mysterious Life of Grape Buds

It wasn't until I took the UC Davis Introductory to Winemaking Course, that I learned that buds that develop into grapes are actually formed during the previous year. No matter how it was stated, I found this concept difficult to grasp. For example, the following description is given in Principles and Practices of Winemaking¹: Starting with a mature, leafless, dormant vine, the buds for this year's crop sprout in early spring already bearing cluster primordia generated the prevous summer.

Then I found an excellent diagram of the cycle in Ronald Jackson's² book: The concise statement that was the caption to this diagram is: Buds develop in the leaf axils in the spring and early summer.
This diagram and the short caption made all the difference in the world for me in understanding what it meant that the buds for this year's crop was formed last year. During the spring, at the same time when the buds are pushing and developing into shoots, the buds for next year's shoots (bud primordia) are being formed in the leaf axil, as shown in the diagram to the left. The weather conditions in the spring and summer are important not only for the developing shoot but also for next year's growth.

The diagram above of the bud primordia shows that contained in this bud are all of the parts needed for the shoot development in the following spring and summer. When the bud grows during the spring, it's almost as if it is telescoping all of the parts that have already preformed in the bud. The above diagram of the bud primordia and the diagram of the shoot is from the UC Davis Online Viticulture Course, VID257 given by Prof. Mike Anderson.
1. 12. Boulton, R.B., Singleton, V.L., Bisson, L. F., and Kunkee,R.E., “ Principles and Practices of Winemaking”, Chapman & Hall, New York, 1995.
Link to Amazon: Principles and Practices of Winemaking, Roger Boulton, et. al
2. Wine Science - Third Edition, Ronald Jackson