Understanding your regional frost calendar is the single most important piece of knowledge for a Canadian outdoor grower. The country spans an enormous range of climates, and your last spring frost date determines when you can safely transplant, while your first fall frost date sets your hard harvest deadline.

BC Coast (Vancouver Island, Lower Mainland): Last frost typically arrives in early-to-mid April, giving coastal growers the longest viable season in the country. Mild, wet falls mean mold vigilance is essential, but the extended window supports large photoperiod plants.

Ontario and Quebec (Southern regions): Expect last frost around mid-May. Toronto and Montreal growers can run full photoperiod plants with a solid late-September to mid-October harvest window. Northern Ontario and Quebec push last frosts into late May or early June.

The Prairies (Alberta, Saskatchewan, Manitoba): Canada's toughest outdoor climate for cannabis. Last frost can run as late as late May to early June, and first fall frost can arrive as early as mid-September. This region strongly favours autoflowering varieties, which can complete their full cycle in 70–85 days regardless of light schedule — meaning a late-June transplant can still deliver a quality harvest before temperatures collapse.

Atlantic Canada (Nova Scotia, New Brunswick, PEI, Newfoundland): Last frosts range from mid-May in Nova Scotia to late May or beyond in Newfoundland. Humid maritime conditions create mold pressure, so strain selection is critical. The harvest window is tight: aim for late September to early October.

For most of Canada, the practical outdoor cannabis season runs from late May transplant to late September or early October harvest — roughly 120 to 140 days. Autoflowers unlock otherwise impossible grows in the coldest zones.

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