Garden 
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The short answer: winterize an irrigation system by shutting off the water supply, then clearing every zone of the water that could freeze inside it — done before the first hard freeze. Turn off the main irrigation valve, shut down the controller or set it to rain mode, then drain the lines by one of three methods: opening manual drain valves, letting automatic drain valves release, or using compressed air to blow the water out zone by zone. The whole point is that any water left in the pipes freezes, expands, and can crack pipes, valves and heads.
Timing matters: do it a week or two ahead of your average first hard frost. We do not install irrigation; our equipment rankings come from aggregated owner reviews and expert consensus, described in how we rank. The full irrigation picture is at the watering and irrigation hub.
What are the steps to winterize?
The sequence is the same regardless of draining method; only the draining step differs by system.
- Shut off the water to the irrigation system at its main valve, usually near where the system taps off the house supply.
- Turn off the controller, or set it to the off/rain mode so it does not try to run a zone over winter. Some controllers keep programs in memory; others need a note of your settings.
- Insulate the backflow preventer and any above-ground piping if they stay in place, and drain the backflow assembly per its valves.
- Drain the zones by manual drain, automatic drain, or air blowout (below), working through each zone.
- Confirm the heads are clear so no water sits in the sprinkler bodies to freeze.
Which draining method do you use?
Your system was built for one of three draining approaches; use the one it was designed for.
| Method | How it works | Best for |
|---|---|---|
| Manual drain | You open drain valves at the low points to let water out by gravity | Systems with drain valves at low points |
| Automatic drain | Valves open on their own when pressure drops below a set point | Systems with auto-drain valves installed |
| Air blowout | Compressed air pushes residual water out zone by zone | Systems that trap water or lack drainage; freeze-prone regions |
Even on a manual or auto-drain system, low spots and sprinkler bodies can hold water, which is why the blowout method is the thorough default in hard-freeze climates.
How does the air blowout work, and is it risky?
In a blowout, an air compressor is connected to the system downstream of the backflow preventer, and each zone is run in turn so the air pushes the water out through the heads. The catch is pressure: too much air pressure can rupture pipes and fittings and destroy sprinkler heads, and the correct pressure is generally kept low — commonly around 50 psi or less for many residential systems, and lower for drip. A typical small homeowner compressor often cannot move enough air volume to clear a zone properly, which is why many people hire a pro for this step. Compressed air is also a genuine safety hazard, so wear eye protection and never stand over a head while blowing out. Drip systems especially need a gentle approach, as covered in how to set up drip irrigation.
What about drip lines, soaker hoses and spigots?
Do not forget the simpler gear that also freezes. Disconnect and drain garden hoses and soaker hoses, coil them, and store them somewhere they will not freeze brittle — a hose left full and connected can freeze and burst, and it can crack the spigot behind it, which is the failure explained in why a hose leaks at the spigot connection. Drain drip tubing and remove and store any hose timers, filters and pressure regulators indoors, since freezing water cracks their housings. Shut off and drain outdoor faucets, and if you have frost-free sillcocks, simply disconnect the hose so they can drain properly.
Done before the first hard freeze, winterizing takes an afternoon and prevents expensive spring repairs. Related questions: do soaker hoses need a pressure regulator?, why a hose leaks at the spigot, and gear in best hose timers.