When cottage gardeners humble-brag about ripe tomatoes, butterflies in their spicebush, or productive black walnuts, go ahead, credit their green thumbs. But you might also point to the latest version of Canada’s Plant Hardiness Zone Map—the one that suggests green thumbs are getting an assist from climate change.
Developed in the 1960s to help growers and foresters select winter-hardy species, the map divides Canada into 19 zones and subzones, based on 30 years of data. Nunavut is in chilly zone 0a, while Vancouver is in 9a, Canada’s warmest zone, with growing conditions now suitable for citrus, such as Meyer lemons, limes, and bitter mandarins. Zone 9a didn’t even exist when the first map was drafted in the ‘60s.
As plant hardiness maps are updated every 10 years or so, they track climatic shifts. The latest version, based on records from 1991–2020 and released last summer, shows about 80 per cent of southern Canada has “increased in hardiness rating,” says John Pedlar, a research scientist with the Canadian Forest Service (CFS). For plants, the rising ratings mean it’s almost like they’ve moved a bit south over the past few decades. Consider the black walnut, a tree with a core range in Ontario that traditionally nestled near the lower Great Lakes. Now, at least a few are found as far north as Sault Ste. Marie, and even Thunder Bay.
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This warming trend is most obvious in western and central Canada. Since the 1990s, Kelowna, B.C., has jumped from 6a to 7a, and the Rocky Mountain foothills town of Diamond, Alta., is up a zone and a half, from 2b to 4a. Meanwhile, Manitowaning, Ont., has climbed a notch to 5b—mild enough that local grape-grower Rick Krasowski includes Niagara-friendly Baco Noir vines among tougher varieties, such as the Nordic-sounding “Louise Swenson.”
For farmed and commercial species, this is mostly good news; people can transplant and tend to them in the right zones. But if growing zones shift too quickly, “We’re expecting to see native plants lagging far behind and likely showing signs of maladaptation,” says Pedlar. That means poorer growth and higher mortality, along with challenges from wildfires, invasive pests, and extreme weather. To prepare for future warming, CFS researchers are already considering a heat-zone map to track plant-scorching warmth.
So keep your green thumb handy. Even with the help of the map, you’ll probably still need it.
This article was originally published in the Early Spring 2026 issue of Cottage Life.
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