Frost damage and recovery... and damage and recovery

Paso Robles has many natural climatic advantages. We don't have to worry about hailstorms in the summer, or rain during harvest. Our humidity is low so mildew isn't usually a big challenge. The chilly summer nights mean that our grapes maintain good acids and get extended hang-times even despite our 320 days of sun each year and our typically hot summer days. But the one natural risk that we deal with each year is spring frosts. And after a decade of avoiding them, 2022 marks their unwelcome return.

During dormancy, frosts are not harmful and in fact usually beneficial. But after budbreak, which began this year in mid-March, any new growth is susceptible to frost damage. Our tools to deal with frosts are limited. We have micro-sprinklers that do a great job, but only enough water to protect our most frost-prone ten acres. We use big fans, which work by mixing the cold air at the surface with the warmer air aloft, to protect our next-most-vulnerable 30 acres. These fans work if there is a defined inversion layer, where above-freezing air is within 10 feet or so of the surface. That happens with a surprisingly large percentage of our spring frosts here, but it's not as reliable as water. As for our other 80 acres of grapevines, on hilltops and steep slopes, they have to fend for themselves. Usually they're OK. 

This year, we first saw some post-budbreak frost nights in mid-April, when several nights saw lows just below freezing and on April 13th temperatures dropped briefly into the upper-20s. Those frosts singed the new growth in several blocks, including some higher blocks that are rarely affected, but they didn't wipe anything out, and it appeared that the frost fans really helped. I would estimate that those frost events cumulatively impacted less than 5% of the property's producing vines, and I was feeling fortunate, on the whole.

Fast-forward to last week. Sometime between 5am and 6am last Wednesday, May 11th, the weather station in the center of Tablas Creek Vineyard registered 30.6°F. That's cold, particularly for this late in the year. And it did some damage in that area, singeing the growth of some of the Tannat, Cinsaut, Counoise, and Syrah. Fortunately, it was below freezing for less than an hour, and it looks like the fan we have set up there kept things from getting too bad. The Cinsaut vine below is on the more-damaged side, and even it isn't a complete loss:

You can see from the above photo that frost manifests itself, at least after a couple of days, in crispy, brown leaves that look burned. Often it's just part of a vine that gets frozen, with areas of damage as you see at the top and other leaves, shoots, and clusters that are fine. It can feel arbitrary or even capricious, and it's not hard if you walk around the vineyard to find vines with one frozen shoot among a dozen green ones, or one surviving shoot among a dozen frozen ones, as in this Syrah vine:

In this central section of the vineyard, which is about 10 acres, I'd estimate damage for our mature sections in the 15% range. That's painful but not crippling. I'm more worried about the two new vineyard blocks in that area, whose young vines got frozen and who don't have the same reserves that older vines do to regrow. I think it's likely that we'll see some vine mortality, but it's too early to know how much.

Unfortunately, a different section of the vineyard got hit much harder. That block, which we call Nipple Flat and whose 11 acres includes blocks of Roussanne, Picpoul, Grenache Blanc, and Vermentino, is at the southern end of the property, closest to Las Tablas Creek. Because it's the property's lowest point, and cold air flows downhill, last Wednesday night was colder, and it stayed cold longer, dropping below 32°F at 3am and bottoming out at 28.1°F at 6:15am. We have a fan there too, but evidently the cold air pooled deep enough that it was blowing below-freezing air around. You can see from the below photo that the swale in the background is all brown, in contrast to the not-quite-as-low section in the foreground that is still green. That lower area (which accounts in my estimate for about 60% of this block) will likely not produce any fruit this year:

This isn't the first time we've seen damaging spring frosts. We lost half our crop due to April frosts in 2001, 2009, and 2011 (I even wrote about our 2011 frost on the blog). Those were a little different, earlier in the year (so the vines were less far out) but more widespread, where our frost fans didn't do any good since even at the tops of the hills the temperatures were below freezing. That meant that everything had to re-sprout, and the damage to our production was roughly relative to how far out they were, with the earliest grapes taking the biggest hit.

Because of our experience in those past years, we know pretty well what happens after April frosts. The frozen shoots die back, but the grapevines have enough vigor to sprout secondary buds, and those buds typically carry half the fruit load of the primary buds. You can see a good example from our April frost, in our Grenache. The frost-damaged shoot was still there this week, almost hidden in the canopy of new growth:

What happens next with the extensively damaged sections of the vineyard is uncharted waters for us, because of how late this frost event was and how far out the vines were. We assume that they will re-sprout and produce new canes and leaves. Evolutionarily, the vines need to photosynthesize carbohydrates and store up that energy to survive the winter and have a go at making fruit in 2023. Will they set clusters? Maybe a few, but I'm not expecting much, because they've spent a lot of their winter reserves in growth that is now damaged. Any crop they do set is going to be a month at least behind, and we'll have to worry about whether it will be able to ripen before (hopefully) rain and (eventually) frost this November.

In terms of impacts to our 2022 harvest, our biggest worry is Roussanne, where the eight acres on Nipple Flat account for roughly three-quarters of our producing acreage. That will have real impacts on how much Esprit de Tablas Blanc we can make and what its blend will be, and likely will preclude a varietal Roussanne. Our bigger picture, though, is not as dire. The badly-affected blocks represent something like 10% of our producing acreage. When you add in the more minor damage in other blocks between our April and May frost events, we're probably looking at something between a 15% and 20% reduction on the crops that we would have had if we'd avoided frosts. That's not nothing: probably 3,000 or 4,000 lost cases of wine that we'd otherwise be making in 2022.

But it could have been worse.