Frosty Mornings

Frosty mornings

Here in southern Oregon, the weather has turned from rainy to clear skies and sunshine. The grape buds have burst and are growing quickly. They already have shoots about 4” long. With the clear skies comes danger of frost damage to the tender shoots. This time of year, despite daytime highs in the 70’s, nighttime lows can easily dip into the 30’s.

And so it has. Three nights in a row, I’ve been awakened by the ‘beep-beep-beep’ of my temperature alarm. I set it at 34 degrees so if there will be frost, I’ll have time to pull on my boots and hurry down to the river. There I start up the 65 hp pump which feeds the overhead sprinklers in the vineyard.

It seems counter-intuitive, but to prevent frost damage, one puts water on the vines so that ice will form on them. As it turns out, a small amount of heat is released by the water as it becomes ice. The plant absorbs this heat. So the plant stays at or close to 32 degrees while the temperature outside the ice gets colder. This buys you 4 or 5 degrees of protection. If it drops lower than that, there will likely be crispy leaves in the morning.

So far (I say this with fingers crossed) the lowest temperature has been 29 degrees. When the sun comes up over the hills, the valley warms ups nicely. Afternoon temperatures have been in the upper 70’s. Spring is here.