How to winterize a sprinkler system

If the ground where you live freezes hard enough to burst a pipe full of water, the system needs to be emptied. That includes the northern states, the Midwest, the Rockies, and much of the transition zone. A mild year is not a reason to skip it. One night in the teens is enough.

Where freezes are rare (south Florida, parts of the immediate Gulf Coast, low deserts that stay above freezing), a full northern blowout can be unnecessary. You still shut the controller off if a freeze is actually forecast, and you follow the water utility if it requires the backflow device protected. Do not copy a Colorado checklist onto a lawn that never freezes, and do not skip the checklist in Kansas because last winter was gentle.

This is also the moment to stop watering a dormant warm-season lawn as if it were July, and to keep watering an overseeded ryegrass lawn that is still green. Those are different schedules. The hardware still has to be protected if a freeze is coming. See the overseeding guide for the rye, and the fall schedule for when the grass itself is done.

Find the irrigation shutoff. It is often a ball valve or gate valve in the basement, crawl space, or a valve box near the water meter, upstream of the backflow preventer. Close it. If you only turn the controller to “off” and leave the supply open, a split pipe or a stuck valve can still run water all night.

Then turn the controller off, or to a rain-hold that will not open valves. University of Minnesota turf guidance and every extension winterizing note agree on this order of ideas: no water supply, no automatic start. A smart controller, including the ones Lawn Dominator connects to, will happily open a zone on a warm afternoon in January if nobody told it the pipes are empty. Empty pipes plus a valve that opens is how debris gets pulled into heads. Set it to off until spring.

Open any hose bibs and drain the short above-ground stubs. Outdoor faucets that are not frost-proof need the indoor valve closed and the outdoor tap opened so the stub can empty.

Some systems have manual drains at the low points, or automatic drains that open when pressure drops. Oklahoma State describes that setup and still tells homeowners to drain the backflow device and any pipe that sits above the freeze line, then insulate what stays outside. Manual drains only work if the pipes were installed with a continuous slope and have not settled into a belly. Colorado State is blunt that gravity draining is not the reliable method, because you cannot see the low spot that still holds a cup of water, and a cup is enough to crack a fitting.

Electric valves are the other limit. Colorado State notes that water sits on top of the valve diaphragm and will not gravity-drain. Those systems get blown out with compressed air.

A proper blowout is air volume, not just pressure. University of Minnesota recommends hiring a certified irrigation contractor for this step. A homeowner pancake compressor can hit a high psi number and still lack the cubic feet per minute to push a slug of water all the way out of a zone. The air rides over the water, the water settles back into the low spots, and you find the crack in April. Minnesota’s reason is safety and damage, not a guild rule.

If a professional, or a carefully used compressor with enough volume, does the blowout, Colorado State’s pressure guidance is the one to hand them: about 40 to 80 psi, with 80 psi as the maximum for rigid PVC and 50 psi as the maximum for polyethylene pipe. Do not exceed what the nozzles are rated for or you will shoot the nozzles off the heads. Blow one zone at a time, the same way you irrigate. Running every zone at once heats the pipe. Colorado State’s rule of thumb: if the heads stay up and air keeps flowing after the water has gone milky and then mostly clear, that zone has had enough. Then move on. Do not stand over a head while it is blowing.

The backflow device stops irrigation water from siphoning into the house supply. It is usually the brass assembly above ground, and it is the part that freezes first. Pressure vacuum breakers and reduced-pressure assemblies must not be blown out with compressed air. Colorado State says the rubber seals can melt from the heat of the air. Atmospheric vacuum breakers, where they are even legal, sit downstream on the zone and get winterized with that zone. Know which device you have before anyone connects a compressor.

After the lines are empty, drain the backflow itself. Colorado State’s sequence for a pressure vacuum breaker: exercise both ball valves and the test cocks, then leave the ball valves about half open and the test cocks open enough that trapped water can expand. A valve left fully open or fully closed holds a pocket of water. University of Minnesota describes the same idea as turning the ball valves to about 45 degrees and cracking the test cocks a quarter turn. Insulate the assembly with a cover made for it, not with a plastic bag that holds meltwater against the brass.

In spring, close the test cocks and ball valves before you pressurize, then open the supply slowly so you do not hammer the pipes. Forgetting that order is how a winterized system gets broken on the first warm Saturday.

Drip tubing and soaker hoses hold less water and still split. Oklahoma State says to drain them and store them out of the sun. If a hose is already frozen, leave it until it thaws. Moving frozen drip tape kinks and cracks it.

Write down the date you shut the system down and which zones you emptied. In spring, walk the zones before you need them. Look for weeping heads, tilted rotors, and a backflow that leaks from a test cock you left open. Then build the watering schedule from a catch-can test, not from last summer’s minutes. The irrigation runtime calculator turns that test into minutes per zone. A lawn that is still dormant does not need the July program on the first 60-degree day.

Lawn Dominator can start and stop runs only on a connected Rachio controller, and the Watering screen has a Stop All control. Turn automation off before the system is drained. B-hyve, Hydrawise, Rain Bird, RainMachine, OpenSprinkler, Netro, LinkTap, and Home Assistant connections import zones and history only, so their schedules have to be turned off on the controller or in the maker’s own app.

If you overseeded ryegrass, keep that zone running as long as the rye needs water and the pipes are safe, and winterize it last.