When to winterize a sprinkler system, and how to do it
Irrigation is the outdoor job that punishes waiting. The pipes are buried, the valves and heads are plastic, and water left in any of them splits the part the first night it freezes hard. Nothing leaks in December. You find out in May, one geyser at a time.
Short answer
Winterize a sprinkler system in the fall, one to two weeks before your area’s average first hard freeze — roughly when overnight lows start touching 28 °F (−2 °C) for several hours. Shut the irrigation supply valve, clear the water out of the lines by draining or blowing them out, insulate the backflow preventer, and switch the controller off.
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What temperature should you winterize at?
The trigger is the first hard freeze, not the first frost. Sources word it slightly differently — some say below 32 °F (0 °C) for several consecutive hours, others point at 28 °F (−2 °C) as the number that actually reaches shallow valves, above-ground backflow preventers and exposed pipe. As of September 2026 the common advice is to look up your area’s average first-freeze date and be finished a week or two ahead of it, rather than waiting for a forecast.
In the United States that puts most of the work in late September to early November up north, earlier at altitude, and late November or December in the southern states. Anywhere else, work from your own average first-freeze date rather than a month on a list. Gable’s library schedules the job for September to November in climates where winters freeze.
Gable’s library: “A $50-100 blow-out vs cracked heads, valves and a backflow preventer.”
How late is too late?
Late is the night the temperature actually stays below freezing for a few hours. Before that, you have time; after it, the damage may already be done and you will not see it until spring. If a cold snap has appeared in the forecast and the system is still full, do the parts you can do yourself today — shut the supply valve, open the manual drains, insulate the backflow preventer — and book the blow-out for the first slot you can get. A partly drained system is in much better shape than a full one.
Do you have to blow out a sprinkler system, or can you just drain it?
There are three ways to get the water out, and which one is enough depends on your system and your winters.
| Method | How it works | Where it falls short |
|---|---|---|
| Manual drain | You open drain valves at the ends and low points of each zone and let the water run out. | Only works if the system was installed with those valves and the pipe slopes to them. |
| Automatic drain | Valves open on their own once pressure drops, so shutting the supply drains the lines. | Water can still sit in heads and in flat runs of pipe. |
| Blow-out | Compressed air pushes water out of each zone in turn. | Needs a compressor that moves enough air, and it is the method that can damage the system if done wrong. |
Neither drain method can prove the pipe is empty, which is why irrigation contractors in genuinely cold regions recommend a blow-out and treat drains as a backup. In mild climates that freeze only occasionally, draining is often treated as enough.
How to winterize a sprinkler system, step by step
- Turn the controller off. Most timers have an Off or Rain position that stops watering while keeping your programme, so you are not rebuilding the schedule in spring.
- Shut the irrigation supply valve. It is usually indoors near where the line leaves the house, or in a valve box. Close it fully.
- Release the pressure. Run one zone from the controller for a moment, or open a test cock on the backflow preventer, so the line is not sitting under pressure.
- Drain, or have the lines blown out. Open the manual drain valves if the system has them, starting at the low points, and drain the backflow device through its test cocks. If the system is being blown out, that replaces this step.
- Insulate the backflow preventer. An above-ground device is the part most likely to crack. Wrap the body and both exposed pipes in foam insulation and tape it snugly, leaving the relief opening clear.
- Leave the test cocks open and the ball valves at about 45°. A ball valve left fully open or fully closed traps a little water inside the ball, which is enough to crack it; half-turned, it drains. Leave the insulation breathable and the relief vent clear rather than sealing the device in plastic.
- Note the date. Spring start-up is the mirror image of this list, and knowing when the system was last serviced is the difference between a plan and a guess.
The same fall trip outside is the moment for the other freeze jobs: winterizing outdoor faucets, sleeving exposed pipes in garages and crawlspaces, and clearing the gutters before the leaves are frozen into them.
Blow-out pressure limits, and the mistake that melts rotor heads
Compressed air is doing something the system was never designed for, and two numbers keep coming up across manufacturer and contractor guidance. Treat them as ceilings, not targets.
- Pressure. Commonly cited limits are about 50 psi for polyethylene pipe and 80 psi for rigid PVC, and never above the maximum operating pressure of the heads on that zone. Poly is the one that lets go first.
- Time per zone. Guidance clusters around one to two minutes of air per zone, in short passes, stopping as soon as the heads are throwing mist rather than water. Dry air spinning a gear-drive rotor with no water to cool it is what melts the gears — a failure you pay for in spring, not in the fall.
- Volume, not just pressure. A small pancake compressor can reach the pressure and still not move enough air to clear a zone, so it runs long instead of hard, which is the wrong trade. Air volume, quoted as CFM, is what actually pushes the water along.
- Open a zone before the air goes in, keep eye protection on, and stay clear of the heads and the blow-out port while the line is charged.
This is why the blow-out is the step most households hire out. As of September 2026, typical US quotes run about $50 to $150 for a system of up to a dozen zones, and roughly $90 comes up repeatedly as an average — a range to expect, not a price, and worth comparing locally.
Which houses need this at all?
Only two things decide it: whether the property has an irrigation system, and whether the winters there freeze. Gable asks both during setup — the sprinkler system is one of the items on the house checklist, and the climate comes from the setup questions — and it only puts the job on your plan if the answer to both is yes. A house where it never freezes is never shown the task, in the same way it is never shown snow or ice-melt jobs.
If you have just taken on a house with a system you have never used, the first-year homeowner guide covers what to find and label before the weather turns, and the full maintenance checklist shows where irrigation sits among the rest of the fall jobs.
Get the reminder in September, not in May
Tick “sprinkler system” when you set Gable up, tell it your winters freeze, and the irrigation shutdown lands on your fall plan with a reminder before the window closes — plus a log of when it was last done. Free trial, then a weekly or annual subscription. No account needed.
