How to Winterize Your Sprinkler System

Winterizing a sprinkler system is one of those tasks that feels optional until a frozen line splits and you're facing a spring repair bill. The work itself takes a weekend afternoon and costs almost nothing—you're just getting water out of places where it'll expand and crack things when temperatures drop. Done right, your system wakes up in spring exactly as you left it. Done wrong or skipped entirely, you'll be replacing sections of lateral line and swapping out damaged zone valves. The timing matters: you want to do this after your last watering but before the first frost.

1. Turn off the main water supply. Locate your main shutoff valve—usually at the backflow preventer or where the line enters the controller—and turn it fully clockwise. If your system has a master valve downstream of the shutoff, close that too. Wait five minutes to confirm pressure has dropped throughout the system.
2. Drain the main line and backflow preventer. Most backflow preventers have a small drain plug at the bottom. Unscrew it by hand or with a wrench and let water run into a bucket until it stops—this usually takes 2-3 minutes. If there's a separate drain valve on the main supply line upstream of the controller, open that too. Leave both drain plugs out.
3. Open all zone valves and bleed manual drain screws. Walk to each zone valve—usually mounted on a manifold near your controller or buried in valve boxes—and open the bleed screw at the top of each one by turning it counterclockwise a quarter turn. Water will dribble out. Leave them open. Also open any manual drain valves you have at low points in your lateral lines.
4. Pressurize the system with compressed air. Rent or borrow an air compressor rated for at least 80 PSI. Turn the compressor on and attach the air line to the main shutoff valve using an air adapter (available at any equipment rental place). Blow air through the system for 20–30 seconds per zone. You'll hear the sprinklers pop and sputter as air pushes remaining water out. Do this slowly—never exceed 80 PSI or you'll damage low-flow heads.
5. Drain the controller and timer lines. If your controller has a separate water line for a rain sensor or master valve, disconnect it at the controller and blow it out with compressed air. Some controllers have internal water-filled circuits for sensor lines—if yours does, open any small drain valves near the controller housing and let them sit open.
6. Close all manual drains and bleed screws. Once blowout is complete, walk the system again and turn all manual drain plugs and zone valve bleed screws clockwise by hand until snug—don't overtighten. If water still dribbles when you think everything is closed, the valve seats have debris; see troubleshooting.
7. Verify the system is sealed and powered down. Turn your controller to OFF or switch it off at the breaker. Walk the entire system one more time looking for any dripping from valve boxes, sprinkler heads, or the backflow preventer. If everything is dry and silent, you're done. If you see drips, the valve body itself is cracked or the seal is failed—mark it for spring replacement.