Two things to celebrate: 2025 frost season ends with no damage and flowering begins under ideal conditions
May 19, 2025
This past weekend was the Paso Robles Wine Festival, our unofficial end to frost season. For the second consecutive year, it was a picture-perfect day, in the 70s and breezy, with both winter's below-freezing nights and summer's hundred-degree days feeling comfortably far away. And yet, as recently as 2022, we saw freezes at this time of year that cost us something like 30% of our crop of white grapes. So it's with a big sigh of relief that we've made it through the first and most dangerous quarter of the growing season intact. We had our first few 90°F days week-before-last, with more expected later this week. As you might expect, the vineyard is growing fast. And on cue, we're starting to see flowing in our early grapes. Here's Viognier:
If you haven't seen grapevines flowering before, you can be excused for finding it underwhelming. It's not a showy process. Still, the tiny white fuzz-like flowers that appear on the clusters are the first stage of development of the berries. From this point on, if the berries are fertilized successfully, they'll grow in size and mass until veraison, at which point they stop growing but accumulate sugar and ripen the seeds within. As with all parts of the vineyard annual cycle, there are grapes that enter (and exit) flowering earlier and later, with the early grapes being Viognier, Grenache, Grenache Blanc, and Vermentino. They are followed shortly by Marsanne and Syrah, and finally, as much as a month after the early grapes, Roussanne, Counoise, and Mourvedre bring up the rear. And there is variation between vineyard blocks as well, with cooler, lower-lying areas a week or two behind the same grapes at the tops of our hills. The other grapes that I could find flowering were the two Grenaches from our top-of-hill blocks. This is Grenache Noir; Grenache Blanc is the last photo in the blog:
Flowering is the second main marker point that we use to compare each vintage to others. First is budbreak (which this year was about a week later than average). Now we have flowering. From the first two markers of 2025, it seems like this year is following a somewhat later path, more like the past couple of wet vintages than most of what we saw between 2013 and 2022. We're at 402 degree days for the season, about 10% less than the average since 2011. Normally, you'd expect a cooler year to come with increased frost risk. Thankfully, that has not been true in 2025.
Typically in April and early May we get a few nights that drop below freezing at our weather station, and another several that do so in our coldest pockets or get near enough that we need to be up at night turning on our frost protection. This year, remarkably, has managed to start cool without any frost nights, and with very few nights that even got close. We did have two nights in early April which dropped to 33.1°F and 33.4°F, but we dodged frost and most of the vineyard hadn't sprouted yet anyway. Since then we've only dropped below 35°F once, and only barely, to 34.8°F on April 13th. That has been a relief, I know, to Austin, Erin, and David, who are on call on spring nights to get up and turn on fans and water to protect us from freezes. For them to have to be up a dozen nights isn't unusual in a normal springtime. We turned everything on this year exactly twice, and for the first time since 2019 saw zero frost damage. Hallelujah.
Flowering is the second of the four viticultural markers that we use each year as markers: notable reference points that indicate where we are compared to other years. These are, in order:
- Budbreak (typically beginning late March or early April, and lasting three weeks or so)
- Flowering (typically beginning mid-May, lasting a month or so)
- Veraison (typically beginning sometime between mid-July and early August, lasting as much as 6 weeks)
- Harvest (typically beginning late August or early September, lasting two months or so)
You might notice that in the above list, the duration of each stage is longer than the previous one. That's because grapes start their growing cycle at different times, and also proceed at different rates. So, harvest stretches over a longer time than veraison, which takes longer than flowering, which takes longer than budbreak. Given we saw flowering begin the second week of May, we're likely to be enjoying the intoxicating scent of bloom until the sometime in mid-June.
What do we want now? We're hoping for consistent, sunny weather to hold through flowering, with only limited wind and no rain. Cold, wet, or windy weather at this stage can produce incomplete fertilization, or shatter, where a cluster has a high proportion of unfertilized berries, looking snaggle-toothed and (often dramatically) reducing yields. Some varieties, most notably Grenache, are prone to shatter, while others are less so. The Paso Robles weather forecast suggests that we're entering a warmer period, with highs over the next ten days between the upper 70's°F and the lower 90's°F, with full sun and no unusual wind. That's perfect.
So far, so good. Full steam ahead.