Here’s the thing that surprises almost everyone: you can shut off the water to your irrigation system, walk away feeling responsible, and still wake up to cracked pipes in April. The valve you closed only stops new water from coming in. The water already sitting in your pipes, valves and sprinkler heads is still there, and when it freezes it expands with enough force to split solid PVC.
Learning how to winterize a sprinkler system properly comes down to one idea: get the leftover water out. Let’s walk through why it matters, the three ways to do it, and the one that’s worth paying a pro for.
What Actually Breaks When Sprinkler Lines Freeze
Water expands by roughly nine percent when it turns to ice. Inside a closed pipe that has nowhere to go, so something gives. The usual casualties are:
- Backflow preventer: It sits above ground, it’s full of water, and it’s the most exposed (and often most expensive) part of the system.
- Valves in the valve box: The plastic bodies crack, and you won’t know until you turn the system on in spring and water bubbles up through the soil.
- Sprinkler heads and risers: The cheap ones split along the seams.
- Buried pipe: Less common where lines are deep, but shallow fittings and elbows can fail.
The nasty part is that none of this shows up until spring. You’ve spent the winter thinking everything is fine.
Know Your Frost Timeline Before You Start
The goal is to finish before your first hard freeze, not after it. In many northern areas that means mid-October to early November. If your local weather service says nights are heading below freezing for several hours, it’s time. Don’t wait for the first morning your car windshield is frosted over; by then the pipes at the surface have already started to get cold.
Warmer climates may only need to protect the above-ground parts (backflow preventer, exposed pipes) with insulated covers. If you’re not sure what your area calls for, a local irrigation company can tell you in a two-minute phone call.
The Three Ways to Drain an Irrigation System
Which method you use depends on how your system was installed. Look in your valve box or near your main shutoff and you’ll usually be able to tell.
1. Manual drain valves
Some systems have small drain valves at the low points of the lines. You open them, the water runs out by gravity, and you close them again in spring. It’s the simplest method, but it only works if the system was built with proper slope and the drains are actually at the low spots.
2. Automatic drain valves
These open on their own when water pressure drops. Shut off the supply, open a test valve or run a zone briefly, and the lines empty by themselves. They’re convenient, but they can stick with dirt and mineral buildup, so it’s worth checking that water actually comes out of them.
3. The blowout method (compressed air)
This is the most thorough way, and it’s what most professionals use. An air compressor pushes the water out through the sprinkler heads, one zone at a time. It’s also the method where mistakes cost you the most, so read the next section carefully.
Real Talk: The Blowout Mistake I See Most
I’ve watched a neighbor do this with a small air compressor he borrowed, cranking the pressure up “to get it all out faster.” Two sprinkler heads shot off like little rockets and a fitting cracked at the valve. He’d done more damage than the freeze would have.
The lesson: more pressure is not better. Too much pressure and too much air volume can damage pipes, heads and valves. Rigid PVC systems and flexible poly-pipe systems tolerate different pressure levels, so check the specs for your pipe type, or the manufacturer’s guidance, before you hook anything up. Always wear safety glasses, never stand over a sprinkler head while it’s running, and never run air through a zone without water having been shut off first.
If any of that sounds uncomfortable, it’s completely reasonable to hire an irrigation pro for the blowout. A one-time service call is usually far cheaper than replacing a cracked backflow preventer.
A Simple Winterizing Checklist
- Shut off the water supply to the irrigation system at the main shutoff.
- Turn off the controller (or switch it to “rain” or “off” mode) so zones don’t try to run all winter.
- Drain the main line by opening the test valve or drain valve near the shutoff.
- Clear the lines using your system’s drain method, or have a pro blow them out.
- Insulate the backflow preventer with a purpose-made cover, not a plastic bag, which traps moisture.
- Leave valves partly open if your system’s guide recommends it, so any trace water has room to expand.
- Write down the date and what you did. You’ll thank yourself in spring.
Common Questions About Winterizing Sprinklers
Can I skip it if we rarely get hard freezes? You can sometimes get away with it in mild climates, but a single unexpected cold snap is all it takes. Protecting the backflow preventer is a cheap safety net either way.
Is one blowout enough? Often yes, but some pros run through the zones twice to clear pockets of water. A second pass is cheap insurance if you’re doing it yourself at a safe pressure.
What about drip irrigation? Drip lines are more forgiving, but the filter, pressure regulator and any above-ground fittings should still be drained and brought inside if possible.
Your Next Step This Weekend
Here’s the standout tip, and it takes five minutes: go look at your system today and figure out which of the three draining methods you have. Find your backflow preventer, locate your main shutoff, and check whether you can see any drain valves. That tiny bit of detective work tells you whether this is a quick DIY job or something to book with a pro.
Then put a reminder on your calendar for two weeks before your average first freeze. Taking the time to winterize your sprinkler system now is one of the cheapest ways to avoid a surprise repair bill in spring, and it keeps your irrigation ready to go the moment the weather warms up.
