The short answer: at least one week before your first hard freeze, which for most of the US falls between October 1 and December 15. The cost of being a week early is zero. The cost of being a week late is the backflow, the valves, and possibly the mainline.
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Use your average first freeze date from NOAA as the anchor, then subtract one week. That is your latest target. Earlier is fine. Later is risk.
| Region | Average first freeze | Winterize by |
|---|---|---|
| Upper Midwest, Mountain West | Late September – mid-October | Late September – early October |
| Northeast, Northern Midwest | Mid-October – early November | Mid-October – late October |
| Mid-Atlantic, Central US | Late October – mid-November | Mid – late October |
| Mid-South (NC, TN, AR) | Mid-November – early December | Early November |
| Deep South (GA, FL panhandle, southern TX) | Late December (if at all) | Mid-December as insurance |
Forecasts are wrong. A freeze projected for Tuesday can hit Saturday night. If you scheduled the blowout for Monday and a Friday cold front arrives early, your system is full of water during the freeze and you find the damage in April.
The one-week buffer also matters because irrigation companies fully book up in October and November. Wait until the freeze warning hits the news and every contractor in your area is suddenly three weeks deep. Set your sprinkler check reminder for two weeks before your target date, book the appointment that day, and you skip the rush entirely.
DIY is possible with the right compressor, but home shop-vacs and pancake compressors do not move enough air. Renting a 10 CFM commercial compressor or hiring a pro for $75 to $150 is the safer call.
For the bill that follows a missed winterization, see the cost of forgetting to winterize.
For most of the United States, the window is between October 1 and December 15. The exact date depends on your average first freeze. Aim to be done at least one week before the first hard freeze, not the first frost.
Standing water in PVC mainlines starts to freeze at 32°F, but real cracking damage usually requires a hard freeze of 28°F or below for several hours. The risk window starts at 32°F, so plan for that as the trigger, not for 25°F.
Not if a freeze is in the forecast. Winterizing two or three weeks before your first freeze is fine. Waiting until after the freeze is the actual mistake. The system being shut down a week early costs you nothing. Skipping the window costs you the backflow.
Any system in a region where overnight lows can hit 32°F needs winterization. That includes the entire US except for southern Florida, southern Texas, and parts of the desert Southwest. Even mild climates with rare freezes need it, because that one unexpected freeze is what cracks the brass.
Two weeks before your average first freeze. That gives you time to book a professional blowout (peak demand in October and November means lead times can stretch to a week) or do it yourself with the right air compressor.
Drain the system manually as fast as you can: shut off the main valve, open every drain valve and the boiler drain on the backflow, run each zone briefly to push out water, and disconnect the backflow if removable. Then book the proper blowout the same week.
Free. No account. The email arrives two weeks before your average first freeze, with enough time to book the blowout before the calendar fills up.
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