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A Gardening Know How report says shutting off a sprinkler system is not always enough to prevent freeze damage: water may remain in pipes, valves and backflow preventers. It advises winterizing before the first hard freeze, while warning that compressed-air blowouts can damage equipment or cause injuries if done improperly. The right method depends on the system and local winter conditions.
A Gardening Know How report advises homeowners to do more than switch off irrigation before winter: water left in pipes, valves and sprinkler heads can freeze, expand and damage system components. The report recommends winterizing before the area’s first hard freeze, but says the appropriate method varies by system and region.
Closing the water supply stops new water from entering, but it may not remove water already held in the system. The report identifies low points in buried pipe, valves and the backflow preventer as places where water can remain. Drain valves may not clear every pocket, particularly if pipes have shifted or do not slope evenly. The report says frozen water expands by about one-eleventh, which can put enough pressure on pipes and fittings to cause cracks or breaks.
For systems designed for a compressed-air blowout, the report describes closing the water supply, connecting a compressor at the system’s blowout port and clearing one irrigation zone at a time. It says to open a zone before applying air, use only enough pressure to move water out, and stop once the heads release a fine mist and air. The report says to make two passes per zone and turn off the compressor before changing zones. It also cautions against sending air through the backflow preventer.
The procedure carries risks. The report warns that excessive pressure can dislodge nozzles or damage pipes and that debris can be propelled from fittings or sprinkler heads. It recommends safety glasses and keeping clear of pressurized components. It says many residential systems can be cleared one zone at a time with airflow around 5 cubic feet per minute, but that is general guidance, not a substitute for the system’s specifications or professional advice.
Preventing Freeze Damage Safely
Winter damage may not become apparent until irrigation is restarted in spring, when split fittings or cracked valves can lead to leaks and repairs. Removing water before sustained freezing can reduce that risk, but an incorrectly performed blowout can itself damage the system. The report’s distinction between airflow and pressure matters: a compressor that is poorly matched to the system, or air applied too forcefully, may leave water behind or harm components.
Timing also matters. The report recommends acting before the first hard freeze, not waiting until pipes are already exposed to prolonged cold. It says an established lawn can be watered less early without lasting harm, though local climate and system design determine what preparation is needed.
sprinkler system winterization kit
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Why a Shutoff May Not Drain Lines
Sprinkler systems include components with different exposure to cold. The report says backflow preventers and exposed pipework face early risk because they are in freezing air. Buried lines are more vulnerable when prolonged cold pushes frost deeper into the ground. A shutoff valve prevents incoming water but does not necessarily empty the network downstream.
Some systems have manual drain valves at low points, and some mild-winter regions use systems without a blowout port. According to the report, shutting off the supply, turning off the controller and draining exposed parts may be sufficient for certain systems in those areas. The source does not establish one method as suitable everywhere; homeowners need to follow their system design and local guidance.
“Airflow (CFM) is just as important, as it determines how much water the compressor can push out of the pipes.”
— Gardening Know How report
System Design Determines the Method
The report does not provide a pressure setting that applies to every sprinkler system, and it notes that system design and regional conditions vary. The 5-CFM figure is presented as sufficient for many residential systems when working one zone at a time, not as a universal requirement. It is unclear from the source what compressor capacity or procedure is appropriate for any particular installation.
Homeowners who cannot identify the blowout port, drain valves or system shutoff should not assume that a generic procedure is safe. The report says some systems are better handled by a professional, but does not specify which models or conditions require one. Local freeze forecasts and the condition of buried lines also affect timing and risk.
Prepare Before Cold Weather Arrives
Homeowners should check their irrigation system’s instructions and arrange any required draining or professional service before the first hard freeze. If using a compressor, the report advises wearing eye protection, keeping people and pets away from pressurized equipment, opening a zone before applying air, and avoiding prolonged blowing after water clears.
After the water supply is shut off and the system is drained or blown out using a method suitable for that installation, the report says to leave the backflow preventer’s ball valves and test cocks half-open so water is less likely to remain trapped. The system’s specific instructions should guide final steps; the source does not give a single procedure for every setup.
Key Questions
Is turning off the sprinkler water enough for winter?
Not always. The report says water can remain in pipes, valves and backflow preventers after the supply is shut off, where it may freeze and damage components.
When should I winterize my sprinkler system?
The report recommends doing it before the first hard freeze. The calendar timing depends on local climate; colder areas may need to act in early or mid-fall.
Can I use a compressor to blow out the lines myself?
Some homeowners do, but the report warns that excessive pressure and improper use can damage equipment or cause injury. Follow the system’s instructions, wear safety glasses, and use a professional if you are unsure about the setup.
What compressor capacity does the report recommend?
It says around 5 CFM is sufficient for many residential systems when clearing one zone at a time. That is general guidance; the source does not provide a universal setting for all systems.
Do all sprinkler systems need a blowout?
No single method fits every installation. The report says some systems in mild-winter regions may need only the supply shut off and exposed parts drained, while other systems retain water that requires more complete winterization.
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