GROWING GUIDE
How to Winterize Sprinklers (Blow-Out Basics)
Winterize sprinklers before a hard freeze: shut off the water, drain the backflow preventer and pump, and get water out of the pipes. Oregon State University Extension says to drain or blow out lines and leave valves slightly open. Do not use an unregulated compressor. If you cannot hold the manufacturer’s pressure, hire the blow-out.
An irrigation system is winterized when the water is off, the backflow preventer and pump can drain, and the pipes are not left full. Oregon State University Extension’s maintenance guide says to drain or blow out pipelines, remove pump drain plugs, and leave valves slightly open so ice has room to expand. Its November calendar adds a specific job: drain a built-in sprinkler system and insulate the valve mechanisms. In Central Oregon, Extension often sees that work in late September or early October, which is earlier than a mild coastal winter. Do the job before a hard freeze, not after a burst pipe. Safety is the other half of the decision. Do not connect a shop compressor unless it has a regulator and a gauge, and do not exceed the pressure the manufacturer allows for your pipe. This page does not invent a PSI. If you cannot set and read that pressure, hire a contractor for the blow-out. Shut the supply first either way.
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How do I winterize the system?
Irrigation winterized means the supply is off, the backflow preventer and pump are drained, valves that can hold ice are slightly open, and the pipes are not left full. A controller set to Off is not that list.
- Shut off the water to the irrigation supply. Do this before you open drains or attach air.
- Open drains and remove the pump plug. Oregon State says water left in a pump cracks it, and valves left tight can crack when ice expands. Leave those valves slightly open.
- Drain or blow out the pipes. Blow-out only with a regulator and a gauge, at or below the pressure your manufacturer allows. This guide does not publish a PSI, because the safe number is on your pipe and heads, not in a national average.
- Insulate the valves and the backflow preventer after they are drained. Oregon State’s November calendar names valve mechanisms specifically.
- Store hoses empty. Do not send an unregulated blow-out through drip tubing.
Central Oregon often does this in late September or early October. A milder coast can be later. The trigger is a hard freeze on the way, which you can see on the frost-date calculator, not a single national week. The rest of the autumn list is the autumn garden.
What can go wrong in a blow-out?
Stand clear of heads while air is on. An unregulated compressor can exceed the pressure the pipe was built for, split a fitting, and throw a nozzle. If you do not have a regulator and a gauge, the decision is to hire the blow-out. Shut the supply first even then.
Common questions
What does winterized mean?+
The supply is off, the backflow preventer and pump can drain, low valves are slightly open, and the pipes are not left full of water. A timer that is merely switched off is not winterized.
Can I blow out the lines myself?+
Only with a regulator and a gauge, and only at or below the pressure your pipe manufacturer allows. This page does not give you a PSI. Without that control, hire a contractor. An open compressor can crack pipe and throw a head.
When should I do it?+
Before a hard freeze. In Central Oregon, Extension often sees blow-outs in late September or early October. A mild coastal winter can be later. Do not wait for a burst fitting to set the date.
What about drip lines and hoses?+
Drain hoses and store them where they will not freeze. Do not send a high-volume blow-out through drip lines unless the drip manufacturer says that pressure is allowed. Insulate valve mechanisms after the system is drained.
Sources & editorial notes
- Oregon State University Extension: inspecting and maintaining irrigation systems
- Oregon State University Extension: November garden calendar
- Oregon State University Extension: fall yardwork and blow-out timing
Sources checked November 4, 2026. Compiled with AI assistance from the linked pages. This is not a Plant Care Steps growing trial. Editorial responsibility.