Understanding Bud Break

bud-breakBud break is a sure sign of spring and the first of four important milestones that mark a vineyard’s growing season.   On April 24, 2013, Cabernet Franc was our first block to reach 100% bud break; the other blocks followed over the next week and by today, May 2nd, the process was complete across the vineyard.

This year’s bud break was about a week earlier than in 2012, with the buds appearing uniform and the process proceeding quickly.  Bud break occurs relatively quickly here in Washington compared to many parts of Napa and Sonoma where I grew grapes for years.  This is due to the colder winter experienced here in Washington, as lower temperatures and longer chill time will usually increase the rate at which bud break occurs.

Although I measure bud break as the point in which leaves begin to unfold, from the wooly bud stage, or bud swell, bud break truly begins in late winter or early spring when water is pumped from the roots up through the grapevine and out through the pruning wounds. This is called bleeding.  Bleeding begins when soil temperatures reach 45-50°F. The movement of water through the plant serves to hydrate the buds as well as deliver minerals, sugars and hormones, which will not only activate metabolic activity in the buds but feed the new growth within the buds resulting in bud swell.

As the new buds begin to form and swell, even prior to swelling, hormones are formed within the buds and move down through the grapevine waking the vines up to new cell growth and cell differentiation. This is the beginning of vegetative growth and is the start of the new season.