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How do you winterize an in-ground sprinkler system?

Updated August 2026

1 hour · Moderate DIY

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You clear an in-ground system with compressed air, zone by zone, in about an hour and never above 50 psi on rigid PVC (80 psi is the ceiling on flexible poly). Shut the water at the isolation valve, put the controller in the off position, then push every zone dry before the first night that drops to 28 degrees. Water expands roughly 9 percent as it freezes, which is enough to split a lateral, crack a brass backflow body, or pop the caps off a row of spray heads.

What you need

Before you start: Compressed air stores energy that water does not. A charged zone can launch a pop-up head or a cap several feet, so wear eye protection and keep people and pets off the lawn while a zone is live. Never close every zone with the compressor still feeding the line, and never exceed 80 psi anywhere in the system. If you have an RPZ backflow assembly or a boiler-fed line you are unsure about, stop and call the irrigation company: a cracked assembly costs more than 5 years of blow-outs.

Steps

  1. Time it to the forecast: blow out after the last watering of the season, before the first night at 28 degrees or lower. Shallow laterals sit 8 to 12 inches down and freeze within a few of those nights.
  2. Shut the system feed at the isolation valve (basement, crawlspace, or meter box), then crack the backflow test cocks a quarter turn to bleed off pressure.
  3. Set the controller to Off or Rain mode, but leave it powered so it holds your programs and clock.
  4. Connect the compressor to the blow-out port downstream of the backflow assembly. Never push air backward through the backflow, which wrecks the internal seals.
  5. Open one zone at the controller before you open the compressor valve, so the air always has an exit. Start with the zone farthest from the compressor.
  6. Regulate the air to 50 psi for PVC or 80 psi for poly, and run a zone no longer than 2 minutes. Stop as soon as the heads throw dry mist instead of water.
  7. Work through every zone, then repeat the whole rotation a second time. Two short passes pull out more water than one long pass and keep the rotor gear drives from running dry and hot.
  8. Disconnect the compressor, leave the test cocks and any manual drains open at 45 degrees, and slip an insulated cover over the above-ground backflow assembly.

Or hire it out

An irrigation company charges $75–150 to blow out a typical 4 to 8 zone yard. A proper tow-behind compressor rents for $60–100 a day, so DIY only wins if you own the compressor or split the rental with neighbors. A freeze-cracked backflow assembly runs $300–800 to replace.

Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for sprinkler blow-outs sets itself.

Log this task, get the next reminder

Frequently asked questions

Can I use my pancake compressor for this?

Not really. A 6-gallon pancake unit puts out 2 to 4 CFM, and a single rotor zone wants 20 to 50 CFM to actually move water instead of just pressurizing it. You will cycle the tank for 20 minutes and still leave water in the line. Rent an 80–185 CFM tow-behind for $60–100 a day, or hire the blow-out. A small compressor is fine for one short drip zone and nothing beyond that.

My lines slope to drain valves. Do I still need a blow-out?

In a hard-freeze climate, yes. Automatic and manual drains empty the mainline, but they leave water in the heads, in the last few feet of each lateral, and in the backflow body, which is the priciest piece to crack. South of the freeze line a drain-down often suffices. From USDA zone 6 north, treat the blow-out as annual and test every zone when you turn the water back on.

When should I turn the system back on in spring?

After the last hard freeze, and slowly. Open the isolation valve about a quarter turn and take 2 to 3 minutes to refill the mainline; a fast refill sends a water-hammer shock through dry pipe and splits fittings. Then run each zone for a minute and watch for tilted heads, geysers from a cracked riser, and dry patches. Budget an hour, because something always shifted over the winter.

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