Frosty organic grapevines.
As the dead of winter passes and visions of spring are in the air, life in the vineyards is once again returning. Our annual pruning work is well underway and we are now in the process of preparing for the eminent bud-break of the vines. With the emergence of fresh green growth on the vines we must have all of our frost protection systems in place.
Spring frost is one of the primary challenges to growing winegrapes on the North Coast of California. From the first signs of emergence from dormancy in early March until the last frosts of May, Mendocino County grape growers must be on call to protect their precious vines from freezing temperatures due to sudden cold snaps. There are a number of agricultural measures which can allow for lower temperatures to occur without damaging vines. These include late pruning to delay bud-break, mowing down cover crops early, increasing cold air drainage out of the vineyard and restricting cold air movement into the vineyard.
Unfortunately, these passive measures are often not enough to eliminate frost damage in colder areas. For the majority of vineyards in Mendocino County the only effective solution to control spring frost events is to use water. The concept behind this technique is based on the latent heat released as water moves from a liquid to a solid state. By continuously applying water to the vineyard, the water changing from a liquid to a solid state on the vines creates heat and protects the vegetation from frost damage, but only down to 25°F
In a standard-sized overhead sprinkler system, we need to supply 50 gallons of water per minute per acre. These rotating head sprinklers wet the entire vineyard canopy and floor. They typically rotate every 30-60 seconds, and 30 sprinklers are needed per acre regardless of the vine spacing or trellis type. Fortunately, we have adequate water supplies in the spring to deliver the quantities of water needed to protect our vineyards during frost events.
Frosty grape leaves on the ground.
The infrastructure necessary to provide the water required to protect our 330 acres of vineyards in Redwood Valley and Potter Valley is quite extensive. We have ponds, pumps, filters, valves, weather stations, thermometers, miles of plumbing and hundreds of sprinkler heads. Not to mention the manpower required to operate and maintain these systems.
On any given night from March through May we have 4 people on call if temperatures drop below 35°F. At this temperature, alarms go off and frost patrol begins. We have to monitor 13 different sites and be prepared to pump water to run sprinklers if any site drops below 33°F.
Frost patrol and protection can be one the most grueling tasks of the year. There are many sleepless nights and stressful mornings for those working frost patrol as there is so much on the line. One night of vines getting burned by frost can ruin the entire crop for more than one vintage.
On the other hand, frost has a number of benefits for grapevines. Cold temperatures slow down the spread of powdery mildew and inhibit many insect pests. Without frost, vines would never go dormant and vine pests and diseases would run rampant. The addition of extra water in the Spring can also help boost vine growth and increase productivity. Without frost patrol, grape growers would have a lot less spring work and a lot less to complain about. Keeping busy definitely helps to keep us out of trouble.
Snow on grape bud.