Saturday April 20th at Vintner’s Festival we had to chill our red wines on ice before serving. The next day, we stayed cool by zip-lining into the reservoir. It’s hard to imagine that just a couple nights prior, Ruben stayed up all night running our frost protection sprinklers.
While the 40+ degree Fahrenheit diurnal swing is one of the most important aspects of our grape-growing environment, it’s also cause for quite a few sleepless April nights. Because of our arid limestone soils and low winter rain fall (this year we only measured 6.5 inches!), our soils don’t retain daytime heat, strengthening the cold inversion layer along the ground during radiation frosts more info
With tiny, delicate leaves and grape clusters already growing; exposure to freezing air “burns” the young growth black. If it’s freezing all night, that young growth will never recover, and the plant must survive on a much more conservative second growth. Frost damage always entails a loss of crop.
As an organic farm, we choose not to burn diesel fuel in smudge pots all night.
Instead, if the temperature starts to sink towards 34 degrees, Ruben turns on the pumps at our reservoir and opens the valves to our network of overhead sprinklers. The sprinklers are strategically placed in the valley-floors of the vineyard and on top of our middle “block A-B” high-density ridgeline to create a misty shroud across the entire vineyard.
For the months of March, April, and May, we rent a second pump to give the sprinklers enough water pressure to effectively spray. The pumps sit on the banks of our 30 foot-deep reservoir to push the water up and over the hills.
In all, the Sprinklers directly spray 20-25% of the vines, but because of the shrouding-effect, the mist of water protects the entire vineyard.
Frost protection through overhead sprinklers takes advantage of the energy release as the sprayed water molecules turn to ice. The air and the plants, surrounded by freezing water droplets are warmer because of the energy release.
Ruben turned the sprinklers on at 11:45 Wednesday night and kept them going through dawn. The temperature ended up getting all the way down to 30 degrees, but we escaped with no burnt vines. The small canopy remains a vibrant bright green throughout the vineyard. Sangiovese is currently in the lead, over six inches high, followed by Viognier, Syrah, Sauvignon Blanc, and in distant last, the perpetually lazy Roussanne.
The long-term forecasts based on current weather patterns, pressure systems, and Pacific Ocean temperatures; indicate we’re done with frost danger for the year. However, the biodynamic calendar warns that there will be frost potential on April 28th.
Our fingers remain crossed despite our beautiful weekend weather!