Winterizing a Sprinkler System: Drain or Blow Out Before Freeze
Winterize an in-ground sprinkler system before the first hard freeze, when nights are forecast to drop into the mid 20s°F. Shut off the main water supply to the system, turn the controller to its off or rain mode, drain the backflow preventer and any above-ground pipes, and clear water from the lateral lines using the system's manual or automatic drain valves or a compressed-air blowout. In most cold-zone yards that window is mid October to early November.
Water left in buried pipes, valves, and especially the backflow device expands as it freezes and cracks fittings. Those cracks often stay hidden until you turn the system on in spring and find a geyser or a soggy patch.
Safety note on blowouts: compressed-air blowouts are the method most irrigation pros use in cold zones, and they carry real risk for homeowners. Compressed air can launch a sprinkler head, valve cap, or fitting with enough force to injure eyes and face, and too much pressure can rupture pipes and damage heads. If you have never done a blowout, hiring an irrigation company is the safer call. If you do it yourself, follow your system manufacturer's instructions, wear safety glasses, keep everyone away from heads and the backflow, and never stand over a component while air is flowing.
Why winterizing matters
- The backflow preventer is the most exposed part. It usually sits above ground near the house and is the first thing to crack in a freeze.
- Low spots hold water. Even systems with drain valves can trap water in dips and valve boxes.
- Spring leaks waste water and money. A cracked lateral line can run unnoticed under turf for weeks.
- Repairs are seasonal bottlenecks. Irrigation companies book up fast in both late fall and early spring.
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- Find the system's main shutoff valve and close it fully.
- Set the controller to off or rain mode so it does not try to open valves with no water.
- Open the backflow test cocks and drain valves per the manufacturer's directions.
- Open manual drain valves at low points, or let automatic drains empty after shutoff.
- For blowouts, use pressure and air volume within the system manufacturer's limits, one zone at a time.
- Wear safety glasses and keep people and pets away from heads during any air purge.
- Insulate the backflow preventer and any exposed pipe with an insulated cover.
- Leave valves in the position the manufacturer specifies for winter storage.
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An insulated backflow cover, a blowout adapter, and foam pipe insulation handle the exposed parts. We may earn a commission at no extra cost to you.
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Drain or blow out: which method fits your system?
There are three common approaches, and your system may be designed for only one.
| Method | How it works | Best for |
|---|---|---|
| Manual drain | Open valves at the low points of each line | Systems installed with manual drains on sloped lines |
| Automatic drain | Spring valves open when pressure drops | Systems with auto drains; still drain the backflow |
| Compressed-air blowout | Air pushes water out through the heads | Most cold-zone systems, especially flat or long runs |
If you do not know which you have, check the installer's paperwork or call the company that put it in. Guessing wrong can leave water in the pipes all winter.
What does a safe DIY blowout look like?
A safe blowout starts with a compressor sized for the job, a regulator, and a firm limit on pressure. Pros typically keep pressure well below what a small home compressor can reach and use high air volume instead. Run one zone at a time, never blow air through the backflow preventer itself, and stop when the heads spit mist instead of water. Never leave a zone running on air with no water, since heads and gear drives can overheat. Many homeowners decide after reading the steps that a pro visit is the better value, and that is a sound choice.
Should you insulate the backflow?
Yes in any zone that freezes. An insulated backflow cover or a wrapped blanket protects the brass body and test cocks from wind chill. Do not wrap it in plastic that traps moisture against the valve. Our outdoor faucet cover guide covers hose bibs and the spigot that often feeds the same system.
What about drip irrigation?
Drip lines and above-ground kits are simpler. Disconnect the timer and filter, bring them indoors, open the end caps, and let gravity drain the lines. Store pressure regulators and battery timers inside where they will not freeze. See our drip irrigation kit guide for setup in spring.
Shop drip and timer storage gear on Amazon
Hose timers and end caps to store indoors, plus safety glasses for any air purge. We may earn a commission at no extra cost to you.
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Zone and timing notes
Zones 3 and 4 should winterize by mid October. Zones 5 and 6 usually have until late October or early November. Zone 7 can often wait until mid November but should still drain the backflow before the first hard freeze. Zones 8 and 9 may only need to protect the backflow and exposed pipes on the few nights that dip below about 28°F; follow local water utility guidance.
Bottom line
Shut off the water, drain the backflow and low points, clear the lines, and insulate what sits above ground before the first hard freeze. Compressed-air blowouts are safest in the hands of an irrigation pro; if you do it yourself, follow the manufacturer's limits and wear eye protection. A properly winterized system turns back on in spring without a single leak.
Related reading
- Outdoor faucet covers and hose care
- Winter lawn care by zone
- Lawn watering guide
- Retractable hose reels
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