Tuesday, November 23, 2010

Cold's worse early


November 23 is awfully early for us to see 22 degrees Fahrenheit in Portland, Oregon. Not in 25 years have we seen such temps in November.
My friend in Lyle Washington (across from Hood River, in the Columbia Gorge) has 5F this morning!
Why do grapegrowers care? Because vinifera can die back to the ground at about 0F to -15F. If there is a graft union somewhere above ground, and the vine winterkills to the ground surface, then that vine loses its ability to ever make vinifera fruit again. The rootstock (which is selected for many features, none of which include fruit quality) may sprout but nobody wants the grapes from it.
Worse, a cold snap in November is harsher on the plants than a cold snap in January. This is because it takes time for the plant to acclimate to winter; one can only imagine the changes which the plant must undergo (sap falls to the roots; leaf stems must be hardened off and rejected; and who knows what else?). Heck, the Harvest was still going on just a few weeks ago, and some vinifera (e.g., Riesling) can be harvested in November. This is very early cold.
Hybrid grapes, which contain the disease resistance and cold resistance of native American grapes, plus the early ripening which may give them more time to prepare for winter, can laugh at cold temperatures, at least until they hit -10F or lower. Some hybrids survive -40F.

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