How to Winterize Your Sprinkler System Before the First Freeze

An in-ground sprinkler system holds water in pipes, valves, and backflow devices that sit just below the surface — and that water expands when it freezes. A single hard freeze on a system that’s still full can split a fitting or crack a valve body, and you won’t find out until you turn the system back on in spring and get a geyser instead of a sprinkler pattern. Winterizing it properly now is a lot cheaper than the repair.

Know What Kind of System You Have

Before doing anything, figure out how your system is built, since that determines how much water actually needs to come out. Most residential systems fall into one of three categories: manual drain (valves at the low points of the system that you open by hand), auto-drain (built-in valves that open automatically once pressure drops), and blowout-required (no drain valves at all, meaning compressed air is the only way to clear the lines). If you’re not sure which you have, look for small drain valves near the low points of the piping, usually close to the backflow preventer or at the ends of zone lines. No visible drain valves usually means you’re dealing with a blowout system.

Shut Off the Water Supply First

Locate the main shutoff valve for the irrigation system — this is separate from your house’s main water shutoff — and close it completely. This stops any more water from entering the system while you work and is the step most people forget, which then undermines everything that follows. If your system has a separate irrigation water meter, this is also a good time to confirm it’s reading zero flow once the valve is closed, which tells you the shutoff actually sealed.

Drain Manual and Auto-Drain Systems

For a manual-drain system, open each drain valve at the low points of the piping and let gravity do the work. Water should flow out steadily; if a valve seems clogged or barely drips, it may need to be cleared with a small wire or replaced before it can do its job. Auto-drain systems handle this step on their own once the main valve is shut and pressure in the lines drops, but it’s still worth manually running each zone briefly afterward to confirm no section is holding standing water. Either way, once the visible flow stops, open the drain at the lowest point in the system and leave it open through winter so any water that seeps back in has somewhere to go.

Blow Out the Lines If Your System Requires It

A blowout system needs compressed air pushed through the pipes to force out water that gravity alone won’t clear, and this is the step where people most often cause damage rather than prevent it. Too much pressure can rupture pipes, blow seals out of sprinkler heads, or damage valve diaphragms. Residential systems typically call for a compressor rated well below what a contractor-grade unit puts out — check your system’s specifications rather than guessing, and if you don’t already own a compressor in the right range, renting one for an afternoon is far cheaper than either buying one you’ll rarely use again or hiring a full-service blowout. Connect the compressor to the system’s blowout port (not just any open valve), open one zone at a time starting with the one closest to the compressor, and run air through each zone in short bursts rather than one continuous blast — watching for a fine mist rather than a steady water stream to know a zone is clear. Never stand directly over a sprinkler head while air is running through it; heads can pop up and eject debris under that pressure.

Protect the Backflow Preventer and Above-Ground Parts

The backflow preventer is usually the most exposed and most expensive component to replace, so it deserves extra attention. Close the isolation valves on either side of it, open the test cocks to release trapped water, and leave them open through winter. If the device sits above ground in a cold climate, wrap it in an insulated cover made for this purpose rather than towels or plastic bags, which trap moisture against the housing instead of keeping cold out. Any above-ground piping, exposed valves, or hose connections near the system should get the same treatment — drained, insulated, or disconnected entirely if they’re not needed until spring.

Don’t Forget the Controller and Timer

With the system physically drained, take a few minutes to protect the electronics too. If your controller is a simple timer, either turn it off completely or switch it to “rain mode” so it stops sending signals to zones with no water in them, which can wear out solenoids over months of dry cycling. Note down your current zone run times and schedule before you do this, since you’ll want to restore the same settings in spring rather than reprogramming from scratch. If the controller is mounted outdoors and isn’t rated for freezing temperatures, check the manufacturer’s guidance on whether it needs to come inside or can stay in place through winter.

When to Do This

Timing matters almost as much as the process itself. Winterize too early and you lose weeks of useful watering for lawns and late-season plantings; wait too long and an unexpected early freeze can catch a full system off guard. A good rule of thumb is to winterize once nighttime temperatures are reliably dropping into the mid-30s, and definitely before the first hard freeze is forecast. If your region tends to get one unpredictable early cold snap before a longer mild stretch, it’s worth keeping an eye on the forecast rather than working strictly off the calendar.