How to Winterize a Sprinkler System Before the First Hard Freeze
Winterize your sprinkler system before the first freeze: shut off the water, drain the lines, and blow out each zone safely — or know when to hire a pro.
- Difficulty
- Intermediate
- Time
- 1–2 hours
- Est. cost
- $0–$75 DIY (hose adapter and fittings); $75–$150 for a pro blowout
- Season
- winter
Last reviewed November 4, 2026
Quick answer
Winterize before the first hard freeze: shut off the irrigation water, drain the backflow preventer, open any manual drain valves, then blow out each zone with compressed air kept at or below 50 PSI. Leave drain valves open and insulate exposed parts for winter. If you have no compressor, no regulator, or a complex backflow setup, a pro blowout (typically $75–$150) is cheaper than one cracked main line.
A sprinkler system is full of water in exactly the places winter attacks first: shallow lateral lines, low-point fittings, and the backflow preventer sitting above ground. When that water freezes it expands by about 9%, and something has to give — usually a fitting, a valve, or a sprinkler head. The damage hides underground all winter and shows up in spring as a soggy patch, a zone that will not pressurize, or a water bill that jumps for no obvious reason. Winterizing takes an afternoon and costs almost nothing if you already own a compressor.
What you need to know before you start
| System type | What winterizing looks like |
|---|---|
| Manual drain valves | Open valves at low points; gravity drains most water; blowout still recommended |
| Automatic drain valves | Valves open when pressure drops; check they actually drain before relying on them |
| Blowout only (no drains) | Compressor required; this is the most common residential setup |
| Backflow preventer above ground | Must be drained and insulated separately — it freezes first |
Find three things before you touch anything: the irrigation shutoff valve (often in a basement, garage, or valve box near the meter), the backflow preventer (usually above ground near the house), and the controller. Take a photo of the backflow preventer's valve positions before you move them, so spring startup is a reversal, not a puzzle.
Materials needed
- Air compressor with a pressure regulator
- Blowout adapter (quick-connect to hose-thread fitting)
- Safety glasses
- Insulation pouches or foam covers for the backflow preventer and exposed pipes
- Pipe insulation or old towels for above-ground runs
- Bucket and towels for drained water
Step-by-step: winterize a sprinkler system
Step-by-step instructions
Shut off the irrigation water and the controller
Close the main irrigation shutoff valve — not the house main, just the line feeding the sprinklers. Then switch the controller to off, or to rain mode if your model has one, so no zone can start on a schedule while you work. If the controller has a backup battery, leave it in place so your programs survive winter.
Drain the backflow preventer
Open the test cocks on the backflow preventer to a 45-degree angle so trapped water drains out, then turn both shutoff handles to a half-open position. This lets any remaining water expand without cracking the brass body. This one device is the most freeze-prone part of the whole system, and also the most expensive to replace, so do not skip it.
Open manual drain valves
If your system has manual drain valves at low points, open them all and let gravity do the first pass. Collect the water or let it drain to a safe spot away from walkways, where it will not freeze into an ice patch. Leave these valves open for winter — closed valves trap the last bit of water exactly where it does the most damage.
Blow out each zone, one at a time
Connect the compressor to the blowout port (usually after the backflow preventer — never blow air backward through it) with the regulator set at or below 50 PSI. Open one zone from the controller, let it blow until only a fine mist comes from the heads, then close it and move to the next. Two minutes per zone is plenty. If a zone blows dry in seconds, it was already mostly drained; if it keeps pushing water after two minutes, stop, let the compressor cool, and run it again briefly rather than forcing it.
Protect above-ground parts and set the controller for winter
Wrap the backflow preventer and any exposed pipe in insulation pouches or foam, and secure them so wind cannot strip them off. Double-check that drain valves are still open and backflow handles are half open. Set the controller to off or winter mode, and note the date — in spring you will reverse these steps in the opposite order.
When to call a professional
Hire a pro if you have no compressor with a regulator, if the backflow preventer is a reduced-pressure type you have never serviced, if shutoff valves are seized or buried, or if your system has a pump that needs its own winterizing. A pro blowout usually runs $75–$150 — a fraction of the cost of digging up a cracked lateral line in April.
The spring payoff
A system winterized properly wakes up in spring with a simple reversal: close the drains, return the backflow handles to their working positions, open the water slowly, and run each zone while you walk it. The hour you spend now is what keeps that spring startup a checklist instead of a repair bill.
Frequently asked questions
- When should I winterize my sprinkler system?
- Before the first hard freeze in your area — typically when overnight lows start dipping near or below freezing for several nights in a row. Water left in pipes, valves, and sprinkler heads expands when it freezes and can crack fittings underground, where the damage only shows up as leaks and dead zones next spring. If a hard freeze is forecast and you have not winterized yet, shut the water off and drain what you can that same day.
- Can I just drain the system instead of blowing it out?
- Sometimes. Systems with automatic drain valves at every low point can drain themselves by gravity, and manual-drain systems can get most of the water out. But low spots, long lateral runs, and heads at the bottom of a slope often hold water that gravity alone will not move. A blowout is the reliable method for most systems; if you are unsure whether yours drains fully, blow it out or hire a pro rather than gambling on a dry winter.
- What air pressure is safe for a sprinkler blowout?
- Keep it at or below 50 PSI for most residential systems with PVC pipe — that is the widely published safe ceiling. Polyethylene pipe tolerates more, but there is no reason to push it: high pressure can crack fittings, blow heads off, and turn a loose fitting into a projectile. Use a pressure regulator on the compressor, never connect an unregulated shop compressor straight to the system, and run each zone for no more than about two minutes so the air does not overheat the pipe.
- Do I need to winterize if winters are mild where I live?
- If your area never sees freezing temperatures, no. But a single unexpected hard freeze can crack an unwinterized system, and many mild-climate regions still get one or two freezing nights a year. If freezes are rare but possible, at minimum shut off the irrigation water, drain the backflow preventer, and insulate any above-ground pipes and valves before the coldest nights.
- What if I forgot and the system already froze?
- Do not run the system to test it. Shut off the irrigation water, let everything thaw naturally, then inspect visible parts — the backflow preventer, above-ground pipes, and valve boxes — for cracks or leaks. When you pressurize the system again in spring, walk every zone and watch for wet spots, low pressure, or heads that do not pop up, which point to underground breaks. A cracked backflow preventer is a job for a licensed irrigation or plumbing pro, because it protects your drinking water.
Sources & references
Related guides
How to Winterize Outdoor Faucets
Disconnect hoses, shut off and drain outdoor faucets, understand frost-free models, and protect plumbing before freezing weather.
How to Prevent Frozen Pipes in Winter
Prevent frozen and burst pipes—insulate vulnerable lines, keep heat on, and know when to shut off water before a freeze.
Winter Home Maintenance Checklist for Homeowners
Cold-weather prep: heating checks, freeze protection, safety devices, and exterior tasks—prioritized for homeowner-safe work.
How to Insulate Exposed Water Pipes
Insulate crawl-space and basement water pipes with foam sleeves—what to cover, fiberglass wrap cautions, and why insulation alone does not stop every freeze.
This guide is for general informational purposes. Conditions vary by home, local codes, and equipment. See our disclaimer.