It’s 3 a.m. and both my cell and home phones ring simultaneously, alerting me of dropping night time temperatures and an imminent threat of frost in the vineyards. I drag myself out of bed and put on a much needed pot of coffee. I know my sleep for the night is over, and the decisions that I make in the next few hours will determine whether millions of dollars of premium wine grapes are harvested come fall.
For Napa Valley Grapegrowers the next couple months are possibly the most stressful time of the year. One mistake and the hope of a successful season can be reduced to crispy dead leaves and shattered hopes of a bountiful harvest.
Longer, warmer days and the onset of spring is once again prompting the emergence of new vulnerable green tissue that we will come to know over the next six months as the foundation for the 2013 vintage. Before we celebrate the success of any growing season, growers have to run a veritable gauntlet of potentially devastating threats, and spring frost is on the top of that list.
As soon as new buds emerge in the first couple weeks of April, they are susceptible to temperatures below 32 degrees Fahrenheit. Freezing water expands in the green tissues’ cells causing irreversible death that translates to a sharp decrease in yields for that season and may affect overall vine health for many seasons to come. Although the science behind frost protection hasn’t changed over time, the way we safeguard our vineyards against freezing temperatures in the spring has. Advancements in farming practices, remote monitoring technology and wireless remote control have greatly contributed to improving the sustainability of frost protection methods.
The first and most effective defense against spring frost is site selection and cultural farming practices. Many vineyards throughout Napa Valley are frost free because they are planted in southern areas like the Carneros where a strong coastal influence from the San Pablo bay keeps night time spring temperatures above freezing.
Other vineyards planted on gentle hillside slopes prevent the settling of colder air and also evade the threat of frost damage. Growers employ frost mitigating tactics such as delaying bud break with late pruning, chopping tall cover crops in the vine rows to allow for more airflow through the vineyard, or even raising the height at which the vines are trained to keep them above the coldest air that settles on the vineyard floor. All these in combination greatly reduce the number of potential frost events a particular vineyard site might incur.
When site selection and farming practices aren’t enough to thwart off the threat of frost damage, more active measures need to be taken. A drive along the valley’s main thoroughfares reveals one of our primary defenses. Hundreds of wind machines extending 30 feet above the valley floor are dotted throughout vineyards to protect five to ten acres at a time by breaking up inversion layers through constant mixing of warmer air from above with cooler air settled around the vines. The mixing raises the overall temperature in the vineyard and can offer good protection when temperatures drop down as low as 28 degrees.
In areas prone to temperatures falling below the protective reach of wind machines the use of water is the gold standard. In 1960 an inexperienced newcomer to the valley planted a vineyard on Oakville Crossroad next to my father-in-law’s family ranch and amongst many generational farmers. He was one of the first in the valley to install a sprinkler system over his newly planted vineyard to the tune of $1,000 per acre. He quickly became the talk of the town as other farmers thought he was foolish for wasting his money. Four years later in the spring of 1964 the valley saw a horrific frost that reduced the overall tonnage that year by over 50 percent. The neighbor was one of few growers in the area who weathered the storm unscathed due to his fancy new system. He was handsomely rewarded for his foresight as word on the street had it that his high-valued fruit paid for his entire ranch that year. Since then use of sprinklers gained popularity and now they can be found on many vineyards especially in the northern part of the valley.
Sprinklers continuously spray water over the vines, and even though ice may form, it remains at 32 degrees — just one degree above the critical temperature when green grapevine tissue suffers damage. Sprinkler systems can also be very useful to temporarily raise the humidity and reduce the temperature in vineyards during very rare but extreme summer heat events that can severely damage fruit close to harvest. These systems are often supplied by reservoirs filled by winter rainfall and recharged by pumping from sumps that collect ground water just beneath the vines via a series of perforated underground pipes called drain tile.
Whether it’s the use of sprinklers or wind machines, it’s in every grapegrower’s best interest to run these active frost protection methods as little as possible to conserve their water, costly fuel, and labor to oversee their operation. In recent years new technology has helped to pinpoint the timing and use of frost protection to reduce or, in some cases, eliminate the need altogether.
Many Napa vineyards are now wired with satellite or Internet-based remote weather stations. They use precise sensors to stream critical weather information to online-based software and growers can monitor falling temperatures in multiple vineyards on one computer screen. Wind machines and sprinkler systems can now easily be operated and monitored remotely with remote control technology. The wiring of vineyards for monitoring and remote control is becoming more cost effective and fuel savings alone often pay for the technology within as little as one frost season.
Just five years ago when spring frost was forecast, I would spend much of the late night and early morning hours on the road with many other grapegrowers in pickup trucks driving ranch to ranch checking temperatures with relatively primitive equipment. I was turning on systems prematurely to allow myself to get to the next ranch in time, and I had no way of knowing if what I turned on stayed on and ran properly throughout the early morning hours. Every frost event felt like an imminent emergency, and I almost always had to call multiple co-workers for help in the middle of the night.
Now, when I answer that early morning phone call, I sit down in front of my computer with a cup of coffee, monitor the current conditions in all our vineyards throughout the valley, and when the precise time comes to turn on frost protection I do so with the touch of a button. I’m proud to know that Napa Valley Grapegrowers are a bit like the new neighbor in Oakville — always searching for a way to improve quality and sustainability even when it means thinking outside the box.
Paul Goldberg is vineyard manager at Bettinelli Vineyards and a director of the Napa Valley Grapegrowers.