How-to Guide
How to Winterize Sprinkler and Drip Irrigation
The short answer
If your ground freezes, irrigation lines must be emptied before winter or the ice will split pipes, fittings, valves, and (most expensively) the backflow preventer. Shut off the system's water supply, shut down the controller, and drain what you can, but Colorado State University Extension is blunt about the limits of gravity: the only positive way to be sure enough water is out is to blow the system out with compressed air, zone by zone, until only mist comes from the heads.
The pressure limits are the safety-critical part: CSU Extension puts ideal blow-out pressure in the 40 to 80 psi range, with 80 psi the maximum for rigid PVC pipe and 50 psi the maximum for polyethylene pipe, and pressure-vacuum breaker and reduced-pressure backflow devices must never be blown out with compressed air. Small home compressors often lack the air volume to clear a zone even at safe pressure, which is why many homeowners hire the blow-out and do the rest themselves. Drip systems are simpler: drain the lines, open the ends, and bring filters, pressure regulators, and battery timers indoors.
The sequence
- 1Shut off the supply — Close the irrigation system's dedicated shutoff, ideally at the point where it will not freeze. Set the controller to off or rain mode.
- 2Drain what drains — Open manual drain valves at low points if your system has them. Automatic drain valves release water at the heads or low points each time pressure drops, but CSU Extension cautions that drains alone cannot guarantee the system is empty.
- 3Blow out zone by zone — With the compressor connected downstream of the backflow preventer, open one zone valve at a time and push air through until heads emit only mist. Keep within the pipe-material pressure limits and never run air through a closed system.
- 4Protect the backflow preventer — Drain it via its test cocks and leave ball valves at a 45-degree angle, or remove and store it indoors where codes allow. PVB and RP devices must never be blown out with compressed air; insulate any above-ground assembly that stays outside.
- 5Finish the loose ends — Disconnect and drain garden hoses, install insulated covers on outdoor faucets, and store hose-end timers indoors with batteries removed.
Compressor sizing, per Extension
Air volume matters as much as pressure. CSU Extension's sizing rule: divide the zone's flow in gallons per minute by 7.5 to get the cubic feet per minute of air required; a zone designed for 20 gallons per minute needs about 2.7 CFM of sustained air. Small shop compressors can reach the pressure but not sustain the volume, leading people to crank the regulator dangerously high to compensate; that is how fittings burst and heads get blown apart. If your compressor cannot clear the zone at safe pressure, hire it out; blow-out services are inexpensive compared with one cracked backflow assembly.
⚠ Never stand over heads or open fittings while air is in the lines, and never exceed the pressure limit for your pipe material: 80 psi for rigid PVC, 50 psi for polyethylene.
Winterizing drip systems
Drip is far more forgiving because the lines are cheap and mostly self-draining. Shut off the water, remove the end caps or open the flush ends, and let lines drain downhill; lift and shake lines that hold water in low spots. Take the vulnerable hardware indoors: the filter, pressure regulator, and battery timer at the head assembly all trap water and crack in a freeze. Poly drip tubing itself usually tolerates winter left in place once open at the ends. If you set your system up from our drip irrigation guide, winterizing is the same head assembly in reverse.
When to do it
Winterize after the last irrigation of the season and before the first hard freeze reaches buried components; a light frost will not hurt buried lines, but do not gamble past the point when night temperatures drop well below freezing. In spring, recharge the system slowly with a partly open valve to avoid water hammer.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Colorado State University Extension - Home Sprinkler Systems: Preparing Your Sprinkler System for Winter — Compressed air is the only positive way to be sure enough water is expelled; ideal blow-out pressures are 40 to 80 psi, with 80 psi maximum for rigid PVC and 50 psi maximum for polyethylene pipe; size the compressor by dividing zone GPM by 7.5 to get required CFM; PVB and RP backflow devices must never be blown out with compressed air.