Sprinkler Winterization Checklist: Shut Off, Drain and Protect
Updated
Figures checked against their sources on ; next check .
Sprinkler winterization checklist
Work through these before freezing nights arrive. Both sources advise a professional blow-out; most of the rest you can do yourself.
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Inspect first
Minnesota's first step: make any repairs or replacements before you shut the system down.
Shut off and drain
Minnesota says it may be indoors in a basement or crawlspace, or outside underground in a valve box.
Clear the lines
Colorado State and Minnesota both advise a professional for this step.
Colorado State says lines settle over time into low spots that benefit from a blow-out even where inline drains are fitted.
Source: Colorado State University Extension, PlantTalk Colorado 2205, Winterizing Sprinkler Systems
Colorado State warns that poorly handled air pressure can damage a system, as can water left in it. Minnesota adds that most home compressors reach the pressure but move far less air than a professional's, so they drain the lines less thoroughly.
Source: Colorado State University Extension, PlantTalk Colorado 2205, Winterizing Sprinkler Systems
Protect the hardware
Trapped water can then drain out of the valves, which prevents cracking when it freezes.
Colorado State says a wrapped preventer keeps the system working longer into the fall. Minnesota suggests foam on exposed pipe and a backflow blanket.
Source: Colorado State University Extension, PlantTalk Colorado 2205, Winterizing Sprinkler Systems
Finish
In short: Shut off the water, open the valves, drain the lines, protect the backflow preventer, and have a professional blow out the lines with compressed air. Both university sources say the blow-out is a job for a certified professional.
Why winterizing matters
Water left in a sprinkler system can freeze, and as it turns to ice it expands. The University of Minnesota's turfgrass program lists what that breaks: burst pipes, above all the exposed pipe around the backflow preventer, and also valves, spray bodies, nozzles and fittings. Colorado State University Extension, writing for a state where fall swings quickly between warm days and hard nights, frames the timing question as a trade: the risk of damage against the need to water a dry landscape.
The two sources agree on the outline of the cure: stop the supply, let the water out, have the lines cleared, and protect what stays above ground. The checklist above follows that order and names the source on every step. Your ticks are saved in this browser only, and the print button gives a clean copy to take outside. Start with the inspection, because a leaking head is easier to spot while the system is running than after it has been drained.
The professional blow-out
Both sources send this step to a professional. Colorado State says to preferably have the system blown out by professionals with an air compressor, and allows that you can do it yourself only with the right compressor, pressure regulation and knowledge. Minnesota goes further and says the best and safest way to winterize is to leave it to a certified irrigation professional.
They give two reasons. Colorado State warns that poorly handled air pressure can damage a system, and so can water left behind in it; it adds that lines settle over time into low spots, which benefit from a blow-out even where inline drains are fitted. Minnesota explains why a home compressor falls short: most can reach the pressure needed, but they move far less air per minute than a professional's machine, so the lines drain less quickly and less thoroughly. This page gives no pressure figure, because neither source does, and a wrong number could break the system.
Protecting the hardware
The backflow preventer is the most exposed part. Minnesota's instruction is to turn its ball valves to 45 degrees relative to the pipe, and to give the screws of the test-cocks a quarter turn so they sit at the same angle. That lets trapped water drain from the valves, so freezing does not crack them. Colorado State adds that wrapping the preventer in insulation covered with plastic, down to ground level and secured with duct tape, keeps the system working longer into the season. Minnesota suggests foam on any exposed pipe and a backflow blanket.
Last, Minnesota says to open the drain valve close to the water shutoff, let the remaining water out, and leave that drain open all winter while the water supply stays off, with a bowl or bucket underneath to catch drips.
Worked example: closing out a system
Work down the checklist in order. Run each zone and note any broken heads or nozzles, and fix them. Close the water at the shutoff between the supply and the backflow preventer, open the valves by hand, and let the valve box drain. Book the professional blow-out. Once it is done, set the backflow preventer's valves at 45 degrees, wrap the preventer, open the drain near the shutoff and leave it open. Finally, check the controller is set to OFF. If the professional who blows out the lines offers to set up the backflow preventer too, Minnesota notes that they should be able to help.
What this checklist does not cover
It does not tell you the date of your first hard freeze; the frost dates lookup gives the typical first fall frost and the earlier date that one year in ten brings, for the NOAA station nearest you. It does not cover pumps, wells or any system with its own manufacturer's winterizing steps, and Minnesota itself notes that steps vary with the age, size and parts of a system, so your installer's manual is the better guide there. If you are thinking about replacing some of the watered lawn altogether, the HOA turf replacement letter helps you ask for approval.