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.”
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.
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.
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.
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.
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.