It’s nearly bud break time in the Yakima Valley, the season of rebirth in the vineyards. Bud break is when the grape starts its annual growth cycle. In the Yakima Valley this stage typically begins in mid-April. If the vines have been pruned during the winter, the start of this cycle is signaled by a “bleeding” of the vine which happens when the sap begins to flow. Bleeding reflects new root growth and warming soil temperatures.
Tiny buds on the vine start to swell and eventually shoots begin to grow from the buds. The shoots sprout tiny leaves that can begin the process of photosynthesis, which creates the energy to accelerate growth. These shoots grow relatively slow until the vines begin to enjoy really warm temperatures (85 degrees and above), which in the Yakima Valley typically occurs in mid-May. It is during this time that the acceleration of growth begins. Growers will easily see 2-3 inches of growth per day, maybe more if it is real warm.
Last year was unusual in that the Valley experienced really warm temperatures earlier in May resulting in an earlier and faster than normal growth.
After bud break, the young shoots are very vulnerable to frost damage. It is during this time that growers go to great lengths to protect the fragile shoots should the temperature drop below freezing. Frost protection in the Yakima Valley includes setting up heaters, wind machines or even applying sprinklers to the vineyard to keep cold air from settling on the vines.
Examples of frost control: Wind machines push the warmer air from a higher elevation toward the vines to help keep warmer air in the vineyard.
Sprinklers are turned on to encapsulate the bud in ice keeping the bud temperature from dropping below 32 degrees.