Sprinkler Winterization Date
See the date to have your irrigation system blown out or drained by, based on the median first frost where you live, and set a reminder so you are not calling after the freeze.
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Data: Daymet (NASA/ORNL) 2015–2024 daily minimums, median first fall frost per town · Updated September 2026
How the winterization date is set
It starts with the first frost
Every town has a median first fall frost, the date by which half of all years have seen 32°F. The tool reads it from a decade of daily temperatures for your town when it can, and otherwise asks which half of the month your first frost usually lands in.
Then it backs up 7 to 10 days
The median is the middle year, so in half of all years the frost comes earlier. Winterizing a week to ten days ahead of the median covers most of those early years without shutting the lawn off in summer.
The backflow preventer is the reason
It sits above ground, full of water, on every irrigation system. A hard freeze cracks its body, and the leak shows up when the water is turned back on in spring. Buried lines and valve boxes split the same way, just less visibly.
Blow-out versus drain
A blow-out clears the lines with compressed air at a controlled pressure and is the usual method in cold climates. Automatic and manual drain valves empty the low points but leave water in the backflow preventer and any uphill runs, so those systems still need a pass by a pro.
Common questions
About 7 to 10 days before the median first frost for your town. In much of the northern half of the country that means late September to mid October; in milder areas it slides into November. The tool gives you the date for your location.
Water left in the backflow preventer, valves and lines freezes and expands. The first hard freeze can crack the backflow preventer, and buried lines can split and show up as wet spots or dead zones next spring.
Draining is straightforward on systems built with drain valves, but a blow-out uses compressed air at a pressure that has to be matched to the pipe and heads. Too much pressure damages the system, which is why most homeowners book an irrigation or plumbing pro for it.
Where hard freezes are rare, most systems skip a full blow-out, but the backflow preventer still needs protecting on the few nights that drop below freezing. A pro can set that up once and show you what to watch.
A valve assembly, usually brass and above ground near where the irrigation line leaves the house, that keeps yard water from flowing back into the drinking water supply. Most towns require one on every irrigation system, and it is the part most often damaged by a freeze.
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