Late Winter Weather in the Vineyard
by Jay DeWitt, Managing Partner and Vigneron
It is Saturday, April 16. I am looking out the window at a snowy blizzard, wondering if the grape buds can withstand these cold temperatures. The grapes at Birch Creek are at the end of dormancy, on the verge of “bud break.” The vulnerability of the tissues changes rapidly during this time. Two weeks ago the tight buds could have withstood a low temperature of 20° for several hours, two weeks from now 32° for a few minutes will kill the green tissues and leave us without a crop. There is not a lot we can do to protect the grapes in these conditions. We have wind machines that are helpful if there is a temperature inversion, but that is not the case during a snowstorm.
The grapes do not all break their buds at the same time, there are varietal differences and differences due to microclimates within the vineyard. The timing of bud break is mostly due to air temperature. If the daily air temperature average is above 50° physiological processes move forward. The first visible evidence that bud burst will happen soon is plants “weeping” from the pruning cuts as the sap moves up from the roots. The buds swell in response, eventually the first leaf will unfold, or “burst” from the bud. The amount of time necessary to move from weeping to bud burst depends on air temperature.
The varietal differences governing the timing of bud break are important. At this time, a few of the buds on the earlier emerging varieties (Syrah, Grenache) have burst, they will be damaged to some degree since there were nighttime temperatures below freezing earlier in the week. The buds on later emerging varieties (Cab Sauv, Merlot) are still tight and should be fine.