Thursday, 2/22/18- It was quite a sight for the morning commuters zipping along Hwy 121 between the towns of Sonoma and Napa Monday this week: curtains of icicles, in some cases reaching all the way to the vineyard floor, hanging from the grapevine trellises of Carneros. No, we didn’t have an overnight cloudburst that made our little corner of the world less Sonoma and more Saskatchewan. It was simply farmers doing what they do best, using a combination of science and smarts, to defend against the latest curve ball from Mother Nature.
The 2018 growing season is shaping up, so far at least, to be a dry and an early one. An historically-dry January and February coupled with some higher-than-average temperatures have lead to an early bud break. Bud break is when the nascent buds, which turn into the coming Harvest’s shoots, leaves and grape bunches, swell with life after winter’s dormancy and begin to spread their leaves in preparation for the upcoming season’s growth. In this case, however, the tender new buds were greeted with a sudden mid-Frebruary cold snap, putting them at risk of freezing in the early hours of the morning. If enough buds suffer cold enough temperatures for a long enough time, the upcoming Harvest yields and quality can be negatively impacted.
Hence the sheets of ice hanging from the trellis wires in Carneros on Monday morning.
There are a few things growers can do to try to mitigate freezing temperatures at night.
Prune late for frost protection: The first round of measures are passive, like pruning as late as you can, which naturally delays a vine’s bud break date a little. However, as pruning has to get done sometime before the weather warms up and as it takes a lot of time and labor to do, it isn’t a realistic solution for every vineyard block.
Mix up the air: For vines already pruned, anti-frost measures have to be a bit more assertive. Cold air sinks, so if you can keep the air in a vineyard moving, the warmer air above the vines will mix in with the coldest air sitting on the vineyard floor. This is why we see so many fans, which look like airplane propellers mounted on telephone poles, in vineyards and why many of us hear those powerful engines firing up on cold nights. Even one degree above freezing helps.
Turn on the sprinklers: If that layer of cold air is just too deep and running the fans doesn’t bring enough warm air into the fruit zone, turning on the sprinklers can be a next line of defense. By creating a thin layer of ice and, critically, by keeping that layer of ice wet, the temperature of the bud won’t get below 32 F. However, if you let the ice dry out and it starts to evaporate, you can actually exacerbate the freeze by the evaporative cooling effect of the water. Similarly, if temperatures get below 23-24 F, this ice shield simply doesn’t offer enough protection. For this reason sprinklers can only be used under very specific conditions. Luckily, any water used this way will sink back into the soil and eventually replenish the vineyard water table.
As you can see, frost protection is a delicate dance and is the biggest reason why growers lose so much sleep between February and May.
So where are the silver linings in all of these threats?
First of all, only a few AVA’s (American Viticultural Areas) and varieties are affected right now so it’s not like a frost-threatened budbreak is a widespread phenomenon. In our Napa and Sonoma vineyards, buds are largely limited to a few spots in Carneros and this cold weather will retard the emergence of other buds, protecting those from exposure.
Secondly, as a winemaker, I’d much rather have an early start to the season than a late ending. So what if I start pulling off my Pinot Noir for rose a couple of weeks earlier than in 2017? So far we seem to be right in line with 2015, and it just means you need to get the winery ready to go a little bit sooner. The real disaster for wine quality comes with a late bud break and a later start to the growing season. As grape ripening gets delayed and Harvest gets pushed further into September, October and in the case of Napa Cabernet, November, the chances for disastrous rains increase. Any grapes still on vine when the fall and winter rainy season begins in earnest are at risk for mold, rot, dilution and a complete loss of flavor and quality. I’ll gladly take an early Harvest over a late one.
Thirdly, thinking of 2017 in Napa and Sonoma Counties, the earlier we get all grapes in the barn, the less risk we have that Harvest will be interrupted by wildfires. Once the grass on the hillsides dries out, technically fires can happen any time but the highest probability occurs in October, after months of hot weather and before the first cold snap and real rains. Begin Harvest a few weeks early and there is a greater probability of having all your grapes safely tucked away in tanks and barrels.
Seeing all that ice in Carneros on Monday morning was dramatic and quite unusual. I’m glad we have these frost-protection options but I’m equally glad that it looks like we’ll be facing a slightly earlier Harvest in 2018 rather than a late one. As with anything to do with Mother Nature, however, stay tuned for how the growing season unfolds as we know the only certainty is change……
Alison Crowe is an award-winning winemaker living in Napa. She is the Winemaker for Garnet Vineyards, Verada Wines and Picket Fence Vineyards in addition to sundry other branded and bespoke wine projects. Alison is also the author of The Winemaker’s Answer Book , enjoys tennis and horseback riding and above so many other things loves a good winter rainstorm.