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How to Winterize a Sprinkler System (Before the First Freeze)

Water left in irrigation lines freezes, expands, and cracks pipes, valves, and sprinkler heads. Here's how winterizing works, why the blow-out method matters, and when to call a pro.

2 min read
In your maintenance planWinterize / blow out irrigation linesSee the cadence, priority, and steps for Lawn & irrigation.

An irrigation system is just a network of thin pipes and plastic heads buried a few inches down — and water that's left sitting in them when winter arrives will freeze, expand, and split them open. Winterizing means getting that water out before the first hard freeze, and in most cold climates it's the single most important thing you'll do for your sprinklers all year.

Why it matters

Water expands as it freezes. Trapped in a sprinkler line, valve, or head, that expansion cracks fittings, ruptures pipe, and shatters the plastic bodies of the heads themselves. The damage hides underground until spring, when you turn the system on and watch geysers erupt across the lawn. Blowing out the irrigation lines every fall is what prevents that.

How winterizing works

  1. Shut off the water supply at the dedicated valve that feeds the system.
  2. Turn off the controller — set the timer to off or rain so the valves don't cycle on through winter.
  3. Protect the backflow preventer above ground: insulate it, and drain it if your method calls for it.
  4. Blow out the lines with compressed air at a safe pressure, working one zone at a time so water is pushed out through the heads.
  5. Confirm every zone runs clear — keep going until only air and a fine mist come out.

Why the blow-out method matters

Simply closing the valve and draining isn't enough where the ground freezes. Water settles into low spots, valve bodies, and head canisters that gravity can't empty. Compressed air pushes it all out. The risk is over-pressurizing — too much air can blow seals and crack heads — so the right compressor size and a careful touch matter. If you're not comfortable with that, this is a worthwhile job to hire out.

In the spring

When the freeze risk passes, reverse the process carefully: start up the system and check every sprinkler head for damage, and test the backflow preventer that keeps irrigation water from siphoning back into your drinking supply.

Make it automatic

Build your free Owner Tools and we'll remind you to winterize before your region's first freeze — and to start the system back up in spring. Free, no login, no address required.

Frequently asked questions

When should I winterize my sprinkler system?+
Winterize before the first hard freeze of the season — generally when overnight lows start dipping toward freezing and staying there. In cold climates that's often mid-to-late fall. Don't wait for the forecast to show a freeze: even one hard freeze on water-filled lines can crack pipes and heads, so get ahead of it.
Do I really need to blow out my sprinkler lines?+
In any climate with hard freezes, yes. Draining alone leaves water trapped in low spots, valves, and heads, and that water expands when it freezes. The blow-out method uses compressed air to push the water out of every zone. In mild climates that never freeze hard, simple draining and insulating may be enough — but where the ground freezes, blow-out is the reliable method.
Can I winterize a sprinkler system myself?+
You can do the shutoff, controller, and insulation steps yourself. The blow-out step takes a properly sized air compressor and care not to over-pressurize the lines, which can damage heads and seals. Many homeowners rent a compressor and do it themselves; others hire an irrigation pro for a quick, guaranteed job. Either way, don't skip it.

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