How to Winterize Your Sprinkler System Before the First Freeze

An in-ground sprinkler system holds water in pipes, valves and a backflow preventer, and water expands as it freezes. A hard freeze on a system that’s still full can split fittings, crack valve bodies or ruin the backflow device, and you won’t find out until spring brings a geyser instead of a spray pattern. Winterizing takes an afternoon, and the method depends mostly on how your system was built.

Quick answer: Before the first hard freeze, shut off the irrigation water supply and set the controller to off or rain mode. Then drain the system: open manual drain valves, let automatic drains work, or blow out the lines with compressed air if your system requires it, using moderate pressure, one zone at a time and never with every zone closed. Drain and insulate the backflow preventer, leave its test cocks partly open, and note your controller settings for spring.

Know Your System Type

System type	How to recognize it	How water gets out
Manual drain	Small valves at low points of the lines, often in small boxes	You open each drain valve
Automatic drain	Special spring-loaded valves at low points, often near heads	They open when line pressure drops
Blowout required	No drain valves; common in many modern systems	Compressed air pushes water out
Drip irrigation	Thin tubing, emitters, a filter and pressure regulator	Open end caps and drain; bring filter and regulator indoors if above ground

If you’re not sure, check the installer’s paperwork or look near the backflow preventer and at the lowest points of each zone for drain valves. Many systems combine methods, and blowouts are also used to finish off manual or automatic drain systems.

When to Winterize

Winterize once nights are reliably near freezing and before the first hard freeze is forecast. A hard freeze is the main risk; a brief light frost usually doesn’t penetrate buried pipes, but exposed parts like the backflow preventer are vulnerable sooner. Don’t shut down too early if a newly overseeded lawn still needs regular watering; hand-water with a hose for the final weeks if needed.

Step 1: Turn Off the Controller

Set the controller to “off” or “rain mode” so it doesn’t try to run zones with no water. Photograph or write down the schedule and run times first. If the controller is outdoors and not rated for freezing temperatures, check the manual; some should come inside or have batteries removed.

Step 2: Shut Off the Water Supply

Close the main irrigation shutoff valve, which is separate from the house main. It’s often in the basement, a crawl space, or in a box near the water meter. Protect that shutoff and any pipe between it and the house from freezing too; it’s part of the system.

Step 3: Drain Manual and Automatic Systems

Manual drain: open each drain valve at the low points, starting at the one nearest the shutoff, and let water drain until it stops. Open the drain at the backflow preventer too. Leave the drains open until spring if your installer recommends it, so any seepage can escape.

Automatic drain: after shutting off the supply, briefly run one zone to relieve pressure, which lets the automatic valves open and drain the lines. Some heads may leak slightly for a few minutes; that’s normal.

Step 4: Blow Out the Lines (If Needed)

Blowing out lines with compressed air is where most DIY damage happens, so go carefully or hire a pro.

Do	Don’t
Use a compressor with enough air volume (CFM) to push water through a whole zone	Rely on a small pancake compressor that can’t keep up
Keep pressure moderate; follow your installer’s or manufacturer’s limit	Use high pressure; it can crack fittings and blow seals
Open a zone before turning on air, and keep one open the whole time	Blow air into a system with all zones closed
Start with the zone farthest from the compressor or highest in elevation, per your installer	Run a single zone for many minutes; dry air heats and damages parts
Work in short cycles, rotating through zones until only mist comes out	Blow air through the backflow preventer
Wear safety glasses and stay away from heads	Stand over heads while air is running

Connect the compressor to the blowout port downstream of the backflow preventer, with the backflow isolation valves closed. Open the first zone at the controller, then slowly let in air. When the heads spray only mist, move to the next zone. Two short passes through every zone clear water better than one long pass. Bleed the air pressure before disconnecting.

Step 5: Protect the Backflow Preventer

The backflow preventer is often the most exposed and expensive part.

1. Close both isolation valves.
2. Open the test cocks with a flat screwdriver, turning them to a 45-degree position to release trapped water, and leave them partly open.
3. Wrap an above-ground unit in an insulated backflow cover made for the purpose. Avoid plastic bags, which trap moisture against the metal.
4. In very cold climates, some people remove the device and store it indoors; only do this if it’s designed to be removed with unions.

Step 6: Check Other Exposed Parts

• Drain and insulate any exposed pipe or valve.
• Bring in drip irrigation filters and pressure regulators if they’re above ground.
• Disconnect garden hoses and winterize outdoor faucets.
• Mark sprinkler heads near driveways and walkways so snow shovels and plows don’t hit them.

Spring Startup

• Wait until the danger of hard frost has passed.
• Close manual drain valves and set backflow test cocks back to closed.
• Open the main supply valve slowly to fill the lines gradually. Opening it fast can cause a water hammer that cracks fittings.
• Run each zone and check for broken heads, leaks and soggy spots.
• Restore your controller schedule, adjusting run times for spring conditions.

Troubleshooting

Problem	Likely cause	Fix
Water still coming from heads after draining	Low spots holding water	Run another short blowout cycle or open additional drains
Heads won’t stop misting during blowout	Normal residual water	Rotate zones; finish when it’s only mist
Backflow preventer cracked in spring	Water left inside or no insulation	Replace; open test cocks and insulate next fall
Valve leaks in spring	Frozen diaphragm or debris	Clean or replace diaphragm; flush the line
Heads leak at startup	Frost damage or dirt in seals	Replace or clean the head

FAQ

Can I just turn off the water and skip draining?

In areas with hard freezes, no. Water left in pipes and valves can still freeze and crack them. In mild climates with only light frosts, draining and insulating exposed parts may be enough.

What PSI should I use to blow out sprinklers?

It depends on your pipe and components, so follow your installer’s or manufacturer’s guidance. Keep pressure moderate; air volume matters more than high pressure for clearing water.

Is it worth hiring a pro for the blowout?

If you don’t have a high-volume compressor or you’re unsure of your system’s limits, yes. The cost is usually much less than repairing freeze damage or blown fittings.

When should I turn my sprinklers back on?

After the risk of hard frost has passed in spring, and when your lawn and plants actually need water.