How Do I Winterize My Sprinkler System?

To winterize a sprinkler system, shut off the water supply to the irrigation line, turn the controller to off or rain mode, drain every zone using one of three methods (manual drain, automatic drain, or a compressor blowout), and protect the backflow preventer. Do it before the first hard freeze — once water trapped in those shallow lines freezes, it expands about 9% and cracks pipes, fittings, and sprinkler heads.

Why sprinklers burst: the shallow-line problem

Sprinkler lines sit only 6–12 inches below the surface — well above the frost line in most northern states. Any water left in them freezes, expands, and finds the weakest point: a PVC fitting, a thin poly line, a sprinkler head, or the backflow preventer. Spring repairs from freeze damage typically run $200–$500+ — heads at $10–$30 each, a cracked backflow preventer at $150–$350 installed, plus line repairs if the damage is underground. A half-hour of fall maintenance avoids all of it.

Tools & materials you’ll need

• Your system’s manual (to find the shutoff valve, drain valves, and zone layout)
• Safety glasses (non-negotiable for blowouts)
• For the manual drain method: just the valve key or handle — nothing else
• For the compressor blowout: an air compressor (minimum ~20+ gallons tank, or a smaller one cycled carefully), an adapter fitting to connect to the blowout port or backflow preventer, and a pressure regulator — never exceed 50 PSI for poly pipe or 80 PSI for PVC
• An insulated cover or pouch for the backflow preventer ($15–$30)
• A bucket or towel for the drained water

Total DIY cost: $0–$40 if you already own a compressor; pro blowout service: $60–$120.

Step 1: Shut off the irrigation water supply

1. Find the main irrigation shutoff valve — usually in a valve box near the house, in the basement, or near the water meter. It’s separate from your home’s main shutoff.
2. Turn it fully off. Ball valves: handle perpendicular to the pipe. Gate valves: clockwise until seated.

Step 2: Set the controller to off or rain mode

Switch the irrigation controller to OFF or RAIN mode. This stops all scheduled watering — the #1 winter sprinkler embarrassment is a system running during a freeze because someone forgot the controller. Leave the controller powered on through winter (OFF mode keeps your programs saved). If you unplug it, photograph the zone settings first.

Step 3: Drain the system — pick your method

There are three ways to get water out. Your system was likely designed for one of them — check the manual or look at what’s installed.

Method A: Manual drain valves

Best for: systems with drain valves at low points.

1. Open each manual drain valve fully and let the water flow out.
2. Open a sprinkler head or two to let air in and help it drain completely, then close the valves after draining.

Method B: Automatic drain valves

Best for: systems with auto-drain valves at low points (common with poly pipe).

1. These valves open on their own when line pressure drops — shutting off the supply is the whole job.
2. Run each zone for a minute or two from the controller to drop the pressure, which triggers the auto-drains.
3. Walk the yard: you should see water weeping out at the low-point valve locations. Auto-drains can clog with sediment — a low spot that doesn’t drain means a valve to clean or replace ($5–$10).

Method C: Compressor blowout (the thorough method)

Best for: any system, and the only reliable method in deep-freeze climates. This is what most pros do.

1. Put on safety glasses — compressed air can blow dirt, insects, and water out of heads at painful velocity.
2. Connect the compressor to the blowout port (usually a threaded fitting near the backflow preventer). Tighten it properly — a loose fitting under pressure whips around.
3. Set the regulator: 50 PSI max for poly pipe, 80 PSI max for PVC. Exceeding it can crack fittings or blow heads off the line.
4. Open one zone at a time from the controller. Never blow air into a closed system — with no open heads, pressure spikes instantly and something breaks.
5. Let air run until heads spray a fine mist, about 2 minutes per zone max. Running a compressor against a dry zone overheats the air and can warp plastic components.
6. Repeat for all zones, then do a second pass — water settles back into low spots.
7. Turn off the compressor and release hose pressure before disconnecting.

Blowout safety — take this seriously:

• Eye protection, always. High-pressure air plus debris is a real injury risk.
• Never exceed the PSI limits (50 poly / 80 PVC). A typical shop compressor can push 120+ PSI — the regulator is mandatory, not optional.
• Never blow into a closed system. A zone valve must be open before air flows.
• Stay clear of heads while they’re blowing — the sudden burst of pressure can be violent on the first zone.

Step 4: Protect the backflow preventer

The backflow preventer is the brass assembly where the irrigation line leaves the house — it stops irrigation water from siphoning into your drinking water. It’s the most expensive single component to replace, so it gets special treatment:

1. Drain the test cocks. The small capped ports hold water — open them, let them drain, then close.
2. Set the ball valves to 45°. Half open: fully closed traps water, fully open exposes seals. The 45° position lets remaining water drain and relieves pressure.
3. Install an insulated cover ($15–$30) — a purpose-made pouch that stays on all winter. In mild climates this plus draining may be all you need.

Step 5: Final checks and spring readiness

• Disconnect and drain any above-ground hoses or quick-connects tied into the system.
• Mark any spots where you noticed weak heads or soggy areas during the blowout — that’s your spring repair list.
• Store the controller manual with your zone map where you’ll find it in April.
• Don’t touch the system again until spring. No “just a quick test” in January — reintroducing water to a winterized system is how pipes burst in February.

What this costs

Safety warnings

• Eye protection during blowouts. Compressed air at 50+ PSI turns dirt and debris into projectiles.
• Respect the PSI limits — 50 PSI for poly, 80 PSI for PVC. A regulator on the compressor is mandatory.
• Never pressurize a closed system. Confirm a zone is open before air flows.
• Don’t use a tiny compressor on a huge system. Undersized tanks cycle constantly; the air gets hot and can damage plastic. Rent a bigger one ($40–$60/day) if needed.
• Backflow preventers are code-required in most areas — don’t remove one to “simplify” winterizing.

Frequently asked questions

When should I winterize my sprinkler system? Before the first hard freeze — when overnight lows drop to the mid-20s °F and stay there. In northern states that’s typically October; in the South, November or December. Your local extension service or a lawn-care company can confirm the usual date for your area. Too early just means a brown lawn; too late means cracked pipes.

Can I just skip winterizing in a mild climate? If your area never drops below freezing (deep South Florida, coastal Southern California), you may not need to — but anywhere that sees even occasional hard freezes, winterize. One surprise freeze is all it takes. The backflow preventer cover alone is cheap insurance in borderline zones.

Is a compressor blowout really necessary, or is draining enough? In mild-winter areas, manual or auto-drain valves are usually enough. In areas with sustained deep freezes, water in low spots, dips, and heads will freeze — blowouts are the only method that clears those.

My compressor is small (6-gallon pancake). Will it work? It can, with patience: run shorter zones, let the tank recharge between passes, and keep the pressure regulated. For large systems (6+ zones, long runs), rent a 20+ gallon unit for the day ($40–$60) — faster, and the air stays cooler.

What does “rain mode” do on the controller? It suspends all watering schedules while keeping your programs saved in memory. The system won’t run, but you won’t reprogram everything in spring.

Do I need to winterize if I have a drip irrigation system? Yes — drip lines and emitters hold water too, and the thin tubing freezes fast. Drain or blow out drip zones the same way, at low pressure (drip lines are fragile — stay well under the 50 PSI poly limit), and remove and store above-ground emitters and filters indoors.

Prevention tips for every fall

• Schedule it. Put a recurring October reminder on your calendar — winterizing is one of those jobs everyone remembers the day after the first freeze.
• Fix the small stuff before winterizing. Replace cracked heads and leaking fittings in fall so spring startup is one step, not a project.
• Photograph your zone layout and controller settings before shutting down. Spring-you will be grateful.
• Inspect the backflow cover yearly. A torn or missing pouch is a $20 fix that prevents a $250 replacement.

When to call a pro

Hire a sprinkler pro ($60–$120 for a blowout) if: you don’t own or can’t borrow a compressor, your system has no drain valves and no blowout port (a pro has the fittings and know-how), you’re unsure where the shutoff is, the backflow preventer is leaking or damaged, or the system is large and complex (10+ zones, pumps, or a well supply). Also call one if spring startup reveals cracked heads, a leaking preventer, or a zone that won’t pressurize — that’s freeze damage, and diagnosing underground breaks is pro territory. A one-time pro blowout is cheap; learning your system’s layout by watching them do it is a bonus that pays off next fall.