What temperatures are Too Cold for Grape Vines?
What temperatures are too cold for grape vines?
For that matter, what temperatures are too hot?
I wasn’t in a “cold frame of mind” until a grower friend informed me in mid-January of an upcoming probable below-zero temperature event on the horizon.
Say what?
When I planned my vineyard in the North Fork Valley (Valley) in western Colorado four years ago, I didn’t hesitate to choose Pinot Noir and Riesling. These varietals made world-class wine, and I had always enjoyed drinking them. I didn’t have the luxury of limitless ground for experimenting with multiple varietals; I had to choose.
Notably, the Valley has a microclimate where both cultivars thrive. The climate tends toward a moderately warm growing season. In the past four years, on average, there were 76 days above 85 degrees. There were no days above 99. Primarily due to our elevation in the Valley—my vineyard is at 5,860 feet—the warm and sometimes hot days are balanced by cool nights.
Importantly, Valley growers and winemakers were doing well with both varietals.
The bane of the Valley is the temperature extremes. Pinot Noir, Riesling, Cabernet Sauvignon, Chardonnay, and many other well-known European Vitis vinifera cultivars are sensitive to extremes.
For example, extreme cold events, commonly called a polar vortex, can compromise a vine’s health by killing growth buds, splitting trunks, and killing vine wood above the ground. The occurrence of any of these items can severely limit a future season’s harvest.
For many Vinifera cultivars, including mine, these conditions occur between 0 to -8 degrees Fahrenheit.
True to the warning I had received, a polar vortex hit Colorado, dropping temperatures below zero in the Valley.
The coldest temp January 19 was 2.3, the 20th brought 3.9 and the 21st (breathe deep), -1.7. The winds were also heightened, with a wind chill of -10 to -15 degrees.
The coldest temp in my vineyard until this event had been 1.4 in 2023. The coldest in 2022 was 3.6 degrees, with 2024 experiencing the warmest coldest temp of all four years of 5 degrees.
Vines are also vulnerable when they’ve not hardened off for winter. See the chart to the left illustrating cold hardiness.
A “killing most vines to the ground” event occurred in western Colorado in October 2020, when the temps dropped abruptly near 10 degrees over two nights.
To the other side of the extreme temperature coin we’re flipping is heat.
Our climate lexicon has expanded over the past dozen years with the increased use and occurrence of heat domes. These events are increasing in number in wine country, having occurred in several west coast and southwest U.S. locales in 2024, and California and Oregon in 2021.
The heat domes regularly maintain daytime temperatures above 105 degrees Fahrenheit for several days running. The events cause stress on the vines, halting photosynthesis, thereby stopping grape sugar production, with berries potentially shriveling and becoming sunburned (if exposed to the sun), and the vines becoming water-stressed.
Historically, the hottest temperature recorded for my vineyard is 99 degrees—97.9 in 2022, 99 in 2023, and 98.2 in 2024.
There are cultivars that better handle temperature extremes, especially the cold. They are called hybrids. Hybrid grapes are a cross between two different varieties, either naturally or from intentional breeding.
Intentional, as is breeding for cold hardiness.
This recent article by Good Fruit Grower, “Wine Grapes Breed to Chill,” discusses several hybrid grapes demonstrating cold hardiness greater than Vinifera, with the capability to make excellent wine. Several of the grapes highlighted in the article are grown in Colorado.
When I planted my vineyard, I didn’t seriously entertain hybrids. I followed a dream based on my personal experiences making and drinking wine.
It may have been shortsighted.
Shortsighted or not, I’m hopeful my vines survived the recent “polar vortex” without much damage. I have a lower section of the vineyard where cold tends to settle—we’ll see.
Excitingly, I’m making my first red hybrid wine made of Marquette from the 2024 growing season. There are many Marquette growers in western Colorado, providing me with an excellent opportunity to experiment making wine from it.
Cheers to the remainder of 2025, with hopefully no polar vortexes or heat domes on the horizon!