What are the pros and cons of rain during the life of a vine?

Rain is on everyone’s mind lately, and we’re all looking at the forecasts for the coming days and weeks. Grape vines, currently in a stage of dormancy, are largely unaffected right now, but what about the long-term outlook?

We talked with five winemakers about the rain. What effect does excessive precipitation have on vines during their other seasonal stages — and what would be ideal, for the best grapes?

“Rains can be a positive or a negative, depending on when the rainfall happens,” explained Jesse Katz, winemaker and founder of Healdsburg’s Aperture Cellars. “I’m constantly checking weather reports and our onsite weather stations. During the growing season, I could be checking on weather hourly, if not more.”

Dormant vines

Grapevines typically being hibernating in late November, when the vines are bare, through February.

To date, the rains have been beneficial for the most part, according to vintners. They’ve filled up vintners’ reservoirs and ponds, allowing these reserves to serve them well for irrigation and frost protection.

But too much rain and vines can experience a condition called “wet feet.” In short, waterlogged vineyards can prevent oxygen from reaching a vine’s roots, eventually hindering the vine’s ability to receive water and nutrients. Erosion is another concern because nutrients can be washed away. Some combat erosion with hay bales.

Bud break

During this stage, typically in early March, the vines awaken from their hibernation and push out buds where the cane of the vine eventually will grow.

While excessive rain during bud break is not cause for concern, stormy weather before bud break could delay this stage.

Bloom

From April to May, bunches of tiny flowers bloom from the new vine shoots. Self-pollinating, each of these flowers has the potential to turn into a single grape.

However, excessive rains in the flowering stage can knock the blooms right off the plant, reducing the number of berries on the vine.

Veraison

Typically in July, veraison signals the onset of ripening, with the green grapes transitioning into red grapes.

After veraison, excessive rains wouldn’t cause a significant problem for thicker-skinned varietals — such as cabernet sauvignon, syrah and petite verdot — because these grapes would be tough enough to withstand stormy weather, winemakers and growers said.

But, for thinner-skinned varietals with tight clusters (examples include sauvignon blanc, chardonnay and pinot noir), excessive rain can be problematic, with fungi developing. While mildew can occur anytime during the growing season, fungi can form on the grapes after veraison.

One example of a troublesome fungus is botrytis, which makes the grapes shrivel and rot, from inside the bunch out. The only vintners who can benefit from botrytis grapes (also known as the noble rot) are those making dessert wines, such as sauternes, a French sweet wine from the region of the same name in the Graves section in Bordeaux.

Ripening

This stage is typically from July to harvest, which can start as early August. And with excessive rains, fungi can form any time after veraison and throughout the ripening stage. One example is botrytis.

Jesse Katz, founder and winemaker of Aperture Cellars, Healdsburg

Question: From now until harvest, what are the potential problems with excessive weather that could affect the quality of the grapes? In other words, what are your worst nightmares?

Answer: We don’t want to see rain during flowering because it can cause shatter (grape clusters failing to reach full maturity), disrupting the self-pollinating process of the vines, and can lead to straggly clusters with fewer berries. Once the vines wake up, assuming the soil profiles are filled (that soils are holding all the water they need), I really prefer to see little to no rain prior to veraison, in particular in red varietals.

Our goal is to have vines stressed due to a lack of water pre-veraison because this has a substantial influence on berry size. We’re wanting smaller berry size to increase skin-to-juice ratio in reds to make the wines more concentrated and expressive of the varietal and site. It’s also a key factor in transitioning the vine from its vegetative cycle to its ripening one.

Rain during the season can sometimes be problematic and raise mildew pressure, and on thin-skinned tight clustered varietals that can cause rot from the inside out. Overall, I think sometimes the concern for a little rain post-veraison gets blown out of proportion, and winemakers who have not worked in other climates can cause themselves unnecessary stress or even lead to poor decisions.

Q: In your mind, do the rains this year mean we’ve overcome the drought?

A: This is a complex question, but the short answer is no. We have years of lower-than-normal precipitation and snowfall, and a wet month or season is not enough to make up for years of drought conditions. We would need multiple years of above-average rainfall, but this is definitely helping.

Q: In your view, are the rains another example of weather extremes in the broader context of climate change or do they signal a return to normalcy?

A: Again, this is a complex question. But, in general, I think we’re seeing extremes become more extreme in our weather patterns.

Arnaud Weyrich, winemaker and production senior vice president at Roederer Estate, Mendocino County

Q: From now until harvest, what are the potential problems with excessive weather that could affect the quality of the grapes? In other words, what are your worst nightmares?

A: There are ways to mitigate excess ground water because we have underground French drains, etc. What we cannot mitigate are effects of very high heat that causes dehydration of your fruit, yield and grape quality loss, as well as smoke from wildfires.

Q: In your mind, do the rains this year mean we’ve overcome the drought?

A: In (agriculture) you have to take it one year at a time. With such a large amount of rain, it means we “banked” water potentially for two years between what the soils absorbed and what’s stored in the ponds. However, nothing much has changed with the fact that we will continue to use water wisely in order to have as much water left at the end of this year, not knowing what the next season might bring.

Q: In your view, are the rains another example of weather extremes in the broader context of climate change or do they signal a return to normalcy?

A: The winter 2022/2023 rain season feels like our 2005/2006 winter rain season. It was relentless and created flooding, slides, etc. in Northern California and in the Anderson Valley. It’s the frequency at which you move from one extreme to the next that seems the new normal and a marker of climate change.

Remi Cohen, CEO of Domaine Carneros, Napa

Q: From now to harvest, what are the potential problems with excessive weather that could affect the quality of the grapes? In other words, what are your worst nightmares?

A: There are risks for vineyard managers throughout the growing season. Drought or excessive rainfall can impact timing and uniformity of bud break. A winter warm spell could cause an early bud break. And if frost occurs after bud break, that has the potential to severely damage vines and impact the harvest.

Inclement weather during bloom, from rain, wind or extreme heat events, can impact the fruit set and the season’s yields. Excessive rain, hail or extreme heat can also cause challenges during ripening that growers will have to endure or mitigate. Until the grapes are harvested and in the winery, there is an array of weather events that could impact the growing season to varying degrees.

Q: In your mind, do the rains this year mean we’ve overcome the drought?

A: As helpful as the above-average precipitation is for this growing season and for snow-pack accumulation, California would need more years of good rainfall to overcome our state deficit. Most of the state has been downgraded from extreme drought status and some areas are doing even better than that, which is a significant improvement from where we were recently. We will see what remains for this year’s winter rainfall and the years ahead.

Q: In your view, are the rains another example of weather extremes in the broader context of climate change or do they signal a return to normalcy?

A: I tend to agree with climatologists who foretell wilder weather swings and an increase in frequency of extreme weather events. The climate is always changing, and I believe these recent changes are in part due to the world’s population and intense use by people.

Randy Peters, co-owner at Kokomo Winery, Healdsburg

Q: From now until harvest, what are the potential problems with excessive weather that could affect the quality of the grapes? In other words, what are your worst nightmares?

A: Rain during harvest is not good because it can cause different kinds of fungi to form on the grapes. But because we live in a Mediterranean climate, we usually hardly get any rain between April and harvest.

Q: In your mind, do the rains this year mean we’ve overcome the drought?

A: Yes, we’re overcoming the drought in Sonoma County. We’re getting enough rain this year to do it. It’s a good thing for the vines to grow without having to add any water.

Q: In your view, are the rains another example of weather extremes in the broader context of climate change or do they signal a return to normalcy?

A: I don’t have a real opinion on that. We’ve had a lot of wet years and about four and a half dry years in the 1970s, and in the 1980s some pretty wet years. The 1990s were in between. We’ve tended to have a lot of ups and downs throughout the seasons over my 40 years in the vineyards.

Joel Peterson, vintner of Once & Future Wines, Glen Ellen

Q: From now until harvest, what are the potential problems with excessive weather that could affect the quality of the grapes? In other words, what are your worst nightmares?

A: Frost, rain during bloom, hail, excessive heat during bloom, high winds during bloom, high fungal pressure, severe heat spikes at any time but especially so post-veraison, rain during harvest.

Q: In your mind, do the rains this year mean we’ve overcome the drought?

A: It’s really too early to make that call. When the drought has lasted as long as the current one, there are changes to the plant and its ecosystem that take a long time to recover. While this rain helps and pushes us in the right direction, if we return to the drought pattern, next year will not matter very much. It’s time to cheer for the current play in this game, but the game is far from over.

The vines this year will certainly be happier, healthier and more verdant. But since cluster counts are determined in the previous spring, frost affects crop and early development and foul weather — hot or cold — influences flowering, it’s hard to say anything about the size or quality of crop for the coming year.

Q: In your view, are the rains another example of weather extremes in the broader context of climate change or do they signal a return to normalcy?

A: Hard to know. I’m a bit agnostic when it comes to questions like this. In the context of the weather generally, which has been erratic and frequently extreme, it would be easy to put it in the climate-change context. Yet, this rain is not the worst we have seen over the many years I have been making wine.

There have been years where the Russian River crested much higher that it has yet to do this year, well before we began talking about climate changes associated with the Anthropocene (Epoch, the period of human impact on Earth). Human effect on the climate has been going on for a long time, since the 1800s and the Industrial Revolution, so perhaps all the weather in my lifetime has been associated with human-caused climate change. It’s just now becoming extreme enough and varied enough that we’re aware of it.

You can reach Wine Writer Peg Melnik at peg.melnik@pressdemocrat.com or 707-521-5310.