If you consume any media at all, you have probably heard about the devastating floods on the East Coast and the unrelenting heat in Arizona, Texas and other southwestern areas.
We have been pretty lucky in California this summer to mostly avoid extreme weather lately, but we did have two days of near-record heat here in the Sacramento area over the 4th of July weekend. Saturday it hit 108 and Sunday was 109. That was followed by some of the coolest weather we’ve seen here in July in over a decade.
Our most immediate concern when it gets that hot is keeping our employees safe, so we were lucky that the hottest days were not work days for many people. As far as our crops, well, the longer it stays hot, the more damage it does. So we again lucked out that the heatwave was relatively short.
Longer heatwaves can also have a spiralling effect where crops ripen too fast for us to keep up with harvest, especially if we are sending employees home early. We managed to avoid that problem completely.
But there’s always a shoe left to drop, and I found it a few days later when I was walking our dog Jack through the table grape vineyard. Thanks to the very chilly spring, the grapes were late to leaf out and they bloomed later than I have seen in 20 years. That is a set up for disaster when the first real hot weather of the season arrives.
At this point you may be saying, “But I thought grapes loved hot weather”. And it’s true, they do — most of the time. In fact, last year we had an amazing grape harvest, despite the fact that we harvested much of the fruit after the September heatwave that produced the hottest weather we’ve ever seen and damaged several of our other crops.
But immature grapes are highly sensitive to hot weather, when they have reached a certain size but before they start to change color and develop sugar — aka, “veraison”. Temperatures over 105 degrees can cause the tiny fruits to shrivel up like raisins, except without the sweet flavor. A nice, leafy canopy can reduce the temperature around the developing grapes to a certain extent. But thanks to the cool weather we’ve had, our canopy is not nearly as well developed as it would normally be by July.
Despite the late bloom, we had a pretty nice crop of baby grapes hanging on the vines prior to the heatwave. Our main concern was actually that the cool and damp weather was creating ideal conditions for powdery mildew that ruins grapes. To combat the mildew, we were spraying garlic oil every week. And to ensure good coverage during spraying, as well as better airflow to keep the humidity down, we had been removing leaves from the vines and trimming them. That strategy had been working nicely to keep the mildew under control. But it left the grapes vulnerable to heat.
As a result, we suffered significant damage. On just about every vine, you can find clusters of grapes that have at least a few shriveled fruits. And in the areas that are most exposed to the sun — those facing southeast and northwest — most if not all of the clusters were partially or completely destroyed.
Now, we’re looking at another 2-3 days of temperatures flirting with 110 degrees. Luckily, some of the grape varietals are turning color right now, which will save them from damage. But others are still a week or two away from veraison. If the forecast verifies, we will be lucky to escape additional damage.
Grapes are not much different from people in that they need time to get used to the heat. The back-and-forth swings we’ve had recently, from almost-record hot to almost-record cool, make that really difficult. But it’s hard to complain about the cool, pleasant mornings we’ve had most of the summer so far and the rest of the crops seem to be enjoying it.