A cracked line costs more to fix in April than winterizing would have cost every year for a decade. It's a 30-60 minute job that gets skipped constantly because nothing bad happens the first time you forget — until the one year it does.
When to do it
North central Kansas usually sees its first hard freeze somewhere in mid-to-late October, but "usually" isn't a plan. Water left in a pipe expands about 9% when it freezes, and PVC doesn't flex enough to absorb that — it splits. The safe rule: winterize before your first overnight low near 32°F, not after. If a cold snap shows up early in your forecast, don't wait for the "real" freeze — get ahead of it.
What you actually need
An air compressor rated for the job — most residential systems need 50-80 CFM at 50-80 PSI for PVC lines, less for poly. A shop compressor from the hardware store usually isn't enough; this is the main reason people hire it out instead of DIY-ing it. You'll also want to know where your backflow preventer, shutoff valve, and each zone's manual drain (if you have them) actually are — figure that out in daylight, not during a cold snap.
The steps
1. Shut off the water supply at the main valve feeding the irrigation system — not just the controller. The controller stops the schedule; it doesn't stop water sitting in the pipes.
2. Connect the compressor to the system, typically through a blow-out port near the backflow preventer or the top of the mainline. If your system doesn't have a dedicated port, this is where hiring it out starts to make more sense than buying fittings for a once-a-year job.
3. Open one zone at a time and blow air through it until the heads stop misting and just push clear air — usually 1-2 minutes per zone. Never run all zones at once; the compressor won't have enough volume to clear any of them properly, and you risk overheating heads that are pressurized with no water moving through to cool them.
4. Watch the PSI, not just the air. Too much pressure through PVC risks blowing a fitting apart, which turns a preventive job into a repair job. Stay in the range rated for your pipe material — if you don't know it, that's a sign to call someone who does.
5. Drain the backflow preventer and any above-ground components by hand — the compressor won't fully clear standing water sitting in a device that isn't sloped to drain on its own. This is the single most commonly skipped step, and backflow preventers are also the most commonly cracked component when people skip it.
6. Set the controller to rain mode or shut it off entirely so it doesn't try to run a schedule against a system with no water in it — that's how solenoids burn out.
The mistakes that cause the callback
Running all zones simultaneously instead of one at a time. Guessing at PSI instead of matching it to pipe material. Skipping the backflow preventer because it's awkward to reach. Leaving the controller live on a schedule. Every one of these is an afternoon's difference in effort and shows up as a spring repair bill instead.
DIY vs. hiring it out
If you've already got a compressor rated for the job and know your system's layout, this is genuinely doable yourself. If you're renting equipment for a once-a-year task, or you're not sure what PSI your lines are rated for, the math usually favors paying someone who already owns the right compressor and does this every week in October — the cost is close to what a weekend rental runs anyway.