With the last two weeks of warm weather, the vineyard has sprung out of dormancy. Starting with Viognier, Grenache and Grenache Blanc, budbreak proceeds through Syrah, Marsanne and Picpoul, and eventually finishes with Roussanne and Mourvedre. The photo below, of a Grenache vine from last week, is typical:
With budbreak comes our annual period of frost danger, which extends roughly through mid-May. That means we have a month of white-knuckle nights while we hope that the radiational cooling doesn't knock our temperatures enough below freezing to damage the fresh growth. So far, we've been OK, and the next week looks relatively warm. But it's a rare year that we see no damage from frost; we've only seen three such years in the last fifteen.
We have two main weapons in our fight against frost damage. The first is water. We have about 20 acres of the vineyard fitted with microsprinklers that we can turn on during frosty nights. Water's unique physical characteristics (that it takes a large amount of energy to move it from 32° and liquid to 32° and frozen) means that as long as you have water flowing, the temperature cannot get below 32°. Unfortunately, even with microsprinklers it takes a lot of water to protect an acre of grapes, and we just don't have reservoirs large enough to protect the entire property.
The second weapon we have is wind. In our typical frost, there is as much as a 10° difference in temperature between the valley bottoms and the tops of our tallest hills, caused by the tendency for colder (heavier) air to flow downhill. Different sorts of wind machines either mix the colder surface air with the warmer air aloft or collect the cold air where it flows and blow it up a chimney a hundred feet or more, preventing it from pooling in low-lying areas. As you might suspect, the mixing wind propellors are more effective in flat areas, and the wind chimneys, which rely on flows of cooler air, require hills and valleys. We use both.
We are also mowing, disking and spading our cover crop, reducing friction at the surface and allowing colder air to drain or be blown away by our wind machines. We're nearly complete with this task and should be totally cleaned up by the end of the week.
Meanwhile, we'll be enjoying the new green growth, the warm spring days, and the growing intensity of the sun. In these benign conditions you can almost hear the vineyard growing. We're keeping our fingers crossed that this continues without a (frost-induced) hitch.