EXPERT ADVISORY – March 20, 2025 – R0038

With the first day of spring officially here and temperatures already hovering around 20 C this week, Niagara grape growers will be keeping a close eye on the temperature swings predicted in the weather forecast.

Brock University Assistant Professor of Biological Sciences Jim Willwerth says that grapevines in the region have overwintered well.

Growers’ attentions have now turned, he says, to being mindful of spring’s warmer daytime temperatures which can threaten the cold tolerance those vines built up during the winter dormancy period.

That’s because large fluctuations, like those expected this week, can also increase the threat of injury to buds, he says.

“Right now, our vines are staying winter hardy, the risk is that if we start getting very warm daytime temperatures in March, they might then lose hardiness quite rapidly,” says Willwerth.

Willwerth’s research conducted with Brock’s Cool Climate Oenology and Viticulture Institute (CCOVI) focuses on climate change and vine resiliency.

“This year we were pretty consistent with the cold, and it hasn’t been very extreme,” he says, noting temperatures only dropped into the -15 C to -20 C range for a few short stretches during January and February.

This contrasts with what happened in British Columbia’s Okanagan Valley over the past two winters, where unusually extreme and prolonged temperatures in the -30 C range devastated grape crops in 2023 and 2024.

Willwerth says vines are presently entering a period known as “deacclimation,” where warmer temperatures will cause the hardiness of the buds to drop.

Just as consistently cold weather in winter is good, says Willwerth, consistently warm daytime temps in early spring can be harmful, confusing vines into thinking it is time to prepare for budding.

If that happens, buds can lose their tolerance to cold, increasing the risk of damage in the event temperatures drop as they are expected to this week.

CCOVI research, says Willwerth, indicates that Niagara’s core varieties such as Chardonnay, Pinot noir and Cabernet Franc have overwintered, as have other varieties with less winter hardiness such as Merlot and Sauvignon Blanc.

And with the movement to buy local products swelling, he says consumers can look forward to robust and healthy Canadian choices on store shelves, both now and in the years to come.

Assistant Professor of Biological Sciences Jim Willwerth is available for media interviews on this topic.

For more information or for assistance arranging interviews:

*Sarah Ackles, Communications Specialist, Brock University [email protected] or 289-241-5483

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