Aim for October 1 to 15. Light frost can show up in Spokane as early as late September, and the first hard freeze, the kind that cracks pipe and backflow brass, typically arrives by mid-October. Booking in September gets you your pick of dates.
A single light frost rarely damages a system. What does the damage is a sustained hard freeze with water still in the lines. If a hard freeze is forecast before your appointment, close the main irrigation shutoff, set the controller to off, insulate the backflow assembly, and keep your appointment.
More: Last call: booking your Spokane sprinkler blowout before the first freeze.
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