Water expands when it freezes. If there is water inside your sprinkler pipes, valves, or heads when winter hits, that expanding ice will crack and destroy your system. Winterizing prevents this. It takes about an hour and saves you hundreds or thousands in spring repairs. Here is how to do it right.
When to Winterize
Winterize when nighttime temperatures consistently drop below 32 degrees Fahrenheit. This is usually October or November in northern states. December or January in southern states. Do not wait until the first hard freeze. By then, surface-level components may already be damaged.
Watch the weather forecast. When you see a stretch of nights below freezing in the 10-day outlook, it is time. Better to winterize a week early than a day late.
Method 1: The Blowout Method (Best for In-Ground Systems)
This is the method the pros use. You force compressed air through the system to push all the water out. It is the most thorough way to winterize. You need an air compressor with enough volume. Not pressure. Volume.
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Required: Air compressor rated at 10 CFM or higher. Smaller compressors do not move enough air. They pressurize the system but leave water inside. Required: Compressed air connection fitting. This screws into your system at the blowout point. Required: Eye protection. Debris can blow out of sprinkler heads at high speed.
Step 1: Shut off the main water supply to the sprinkler system. There should be a dedicated shut-off valve near the backflow preventer or water meter. Step 2: Open any drain valves in the system. This lets gravity drain what it can before you start blowing. Step 3: Connect the air compressor to the blowout fitting. The blowout port is usually on the downstream side of the backflow preventer. Step 4: Set the compressor to 50 PSI maximum. Higher pressure can blow fittings apart. Start low. Step 5: Activate the zone farthest from the blowout point first. Step 6: Open the air valve slowly. Watch the sprinkler heads. Water will spray out first. Then a mist. Then just air. When only air comes out, that zone is clear. Step 7: Close that zone and move to the next. Continue until all zones blow only air. Step 8: Turn off the compressor. Disconnect the air line. Leave all drain valves open.
Important: Never leave the air running on a zone for more than 2 minutes. The air heats up as it compresses and can damage plastic components if run continuously.
Method 2: The Drain Method (For Systems With Auto Drains)
Some systems have automatic drain valves at low points in the piping. When water pressure drops, these valves open and let water drain out by gravity.
Step 1: Shut off the main water supply. Step 2: Open the manual drain valves. They are usually at the lowest points of the system. Step 3: Open the test ports on the backflow preventer. Use a flathead screwdriver to turn the test cocks to a 45-degree angle. Step 4: Let the system drain for at least 30 minutes. Step 5: Close the drain valves.
The drain method is easier than blowing out the system. But it is less reliable. Auto drains can clog with dirt and debris. If a drain clogs, water stays in that section and freezes. If you rely on auto drains, test them in the fall by shutting off the water and checking that each low point actually drains.
Method 3: Insulation Method (For Mild Climates Only)
In areas where freezes are rare and brief, you can winterize by insulating instead of draining. This only works in USDA zones 8 and above. If you get hard freezes every winter, you must drain the system.
Step 1: Insulate above-ground pipes with foam pipe insulation. Step 2: Wrap the backflow preventer with an insulated cover. Do not just wrap it in a towel. Use a proper insulated backflow cover. Step 3: Cover the valve manifold box with insulation. Foam board or an insulated blanket works. Step 4: If a hard freeze is forecast, run the system for a few minutes before the freeze. Moving water is harder to freeze than still water.
This method is not as reliable as draining. I have seen insulated systems still freeze and break during unexpected cold snaps. If in doubt, drain it.
What to Do With the Controller
For in-ground controllers, set the mode to Off or Rain Mode. Do not unplug the controller. The internal battery that saves your programming needs power to stay charged. Just turn off the watering schedule.
For hose-end timers like the Melnor AquaTimer, remove them completely. Disconnect from the spigot. Remove the batteries. Store indoors. Water trapped inside the timer will freeze and crack the housing. Bring drip irrigation filters and pressure regulators inside too.
Spring Startup Checklist
When spring arrives and freezes are past, here is how to restart. Step 1: Close all drain valves. Step 2: Close the test cocks on the backflow preventer. Step 3: Slowly turn on the main water supply. Open the valve very slowly. A sudden rush of water can break fittings. Step 4: Run each zone manually. Check for leaks. Check that heads pop up and spray correctly. Step 5: Adjust any heads that shifted during winter. Step 6: Set the controller schedule and turn it back on.
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