A sprinkler line that still holds water on the first truly cold night can split, and you won’t find out until the system runs in spring. In southern Ontario, plan to finish the shutdown in the first half of October, before the average first frost arrives. Farther north, start earlier. The work itself is a sequence: hoses off, interior shutoff closed, outdoor taps drained, sprinkler lines cleared of water.
When to do it in Ontario
Aim for the first half of October, and treat October 16, the average first fall frost at Toronto Pearson, as the far edge of that window rather than the target. The rule that protects pipes is to finish before the first hard freeze, not after the first light one.
Why the average date isn’t a safe date
The October 16 figure comes from Environment and Climate Change Canada’s Canadian Climate Normals for 1981-2010, read at the Toronto Lester B. Pearson station. It is a mean. In about one year out of two the first frost falls later than that date, and in the other half it falls earlier. Waiting for October 16 means losing the coin flip every second fall. The Canadian normals also cover an older period than the 1991-2020 figures usually quoted for US frost dates, so don’t line the two up too neatly.
A light frost and a hard freeze are different events. The first light frost blackens basil and tomato leaves, then often gives way to a stretch of mild afternoons. Plumbing barely notices it. A hard freeze is a night that stays cold long enough for water sitting in exposed pipe, valves and tap barrels to turn solid. The trouble is that the light frost makes people relax. The garden has been nipped, the days warm up again, and the sprinkler shutdown slides to the last nice weekend of the month. That weekend is the gamble.
Where Ontario moves the window
Nothing about Ontario’s winter makes a full shutdown optional. Environment Canada’s 1981-2010 normals for the Toronto reference station put the mean daily minimum of the coldest month at -10.2 °C…
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Sprinkler lines: drain or blow out
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Outdoor faucets and hoses
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What goes wrong here
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Common questions
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