How to Winterize Your Irrigation System
In-ground sprinkler systems hold more water than most homeowners realize—hundreds of feet of buried PVC, bronze valves, and plastic heads all full of liquid that becomes a pipe-cracking solid at 32F. Winterization removes that water using compressed air, and done right it costs less than a single split lateral line. Done wrong, or skipped entirely, you are buying a new backflow preventer in the spring.
Quick Summary
Time Required
1–2 hours
Difficulty
Hire a pro
Cost
$75–$150 professional
Shut Off the Water Supply to the Sprinkler System
Before the blow-out begins, the irrigation supply must be isolated from the rest of your household plumbing. This prevents a catastrophic backflow of compressed air into your home's potable water lines.
Locate the irrigation shutoff valve
Most systems branch off the main water supply just inside the house, typically in a basement or utility room near the water meter. Look for a dedicated ball valve tagged or labeled “irrigation” or “sprinklers.” If yours is not labeled, trace the pipe leading to the exterior backflow preventer and identify the nearest shutoff.
Close the valve fully and drain the riser
Turn the ball valve lever perpendicular to the pipe to shut it. Open the test cocks on the backflow preventer outside to drain the short section of pipe between the house and the preventer. This reduces the water the technician will need to push out through the zones.
Label the valve for next year
If you had to hunt for the shutoff, tie a luggage tag on it now that reads “Irrigation shutoff—closed for winter.” Future you, or the next homeowner, will thank you. This is also useful during plumbing emergencies when any household valve needs to be located quickly.
The Compressed-Air Blow-Out and Why Pros Do It Better
The only reliable way to winterize a sprinkler system is to physically push all the water out of the buried lines with compressed air. The challenge is that this takes far more airflow than a typical home compressor can produce.
Why Compressor Size Matters
- CFM vs PSI: Pressure (PSI) opens sprinkler heads, but volume (CFM) actually moves water out of the pipe. A pancake compressor might hit 150 PSI but only delivers 2–4 CFM, which is like trying to empty a swimming pool with a straw.
- Pro-grade requirement: A proper sprinkler blow-out needs 80–200 CFM at 40–80 PSI. That is a tow-behind diesel compressor the size of a refrigerator, the kind pros haul in a trailer.
- Pressure limits: Too much pressure cracks glued PVC fittings and shatters plastic nozzles. PVC systems cap at 80 PSI, poly pipe caps at 50 PSI. A pro gauges and throttles to match your system.
- Heat damage: Running an undersized compressor for too long blows hot compressed air through plastic gears inside the heads. Without a trailing column of water to carry heat away, gear-drive rotors can melt internally—expensive and invisible damage.
Controller Settings and the DIY Decision
Even with a professional blow-out scheduled, you have two jobs on the controller and one decision to make about whether to DIY. Modern Wi-Fi controllers make the controller step especially easy.
Set the controller to rain or off mode
On older controllers, turn the dial to “Rain” or “Off.” On smart controllers, use the app to enable seasonal suspend or winter mode. This preserves your zone schedule and seasonal adjustments so you do not have to rebuild them in spring. Do not cut power to the controller—the backup battery will die and reset the time.
Assist during the blow-out
The technician will ask you to cycle through zones manually from the controller while they watch the heads. Zones are blown out one at a time, usually starting farthest from the compressor. Each zone runs until mist stops and only air comes out, typically 2–5 minutes per zone.
Weigh the DIY pros and cons
DIY saves $75–$150 per year but requires renting a 100+ CFM compressor ($60–$120 per day), hauling it home, and safely managing pressure to avoid destroying your system. For a small 4-zone lawn it may be worth it, but for systems with drip lines, multiple zones, or expensive rotor heads, the pro's large compressor and experience reading each zone make their $100 the better deal.
Marking Heads, Protecting the Backflow, and Timing
After the lines are clear, two tasks protect the system from physical winter damage: marking everything a plow might hit, and insulating the above-ground backflow preventer so trapped residual water cannot still freeze and crack brass.
- Flag the heads near plow routes: Push bright marker flags (orange, pink, or yellow) into the ground next to every sprinkler head within 6 feet of driveways, sidewalks, or curb lines. Plow operators working in the dark or in heavy snow cannot see heads below the snow surface and will rip them out of the ground along with the underlying riser.
- Insulate the backflow preventer: The above-ground brass or bronze backflow device is the single most vulnerable component. Even after a blow-out, small amounts of water can pool between check valves. Wrap the assembly in closed-cell foam insulation or an insulated pouch sold by irrigation suppliers, then cover with a waterproof plastic bag secured with zip ties. Leave the test cocks slightly open so any expanding water has an escape path.
- Schedule 2–3 weeks before first freeze: In most of the northern United States that means booking for the last two weeks of September, executing in the first two weeks of October. Do not wait until a freeze warning—irrigation contractors are fully booked by then and you will be gambling with 20F overnight lows.
- Document the process: Take photos of the backflow preventer, marker flag placements, controller setting, and the blow-out receipt. Next October you will have a reference for where the heads are and when to schedule, and the receipt supports any warranty claim if a freeze-damaged component fails anyway.
Pro Tips
- •Book the same company every year: Many irrigation companies put repeat customers on a recurring fall schedule automatically. You skip the phone tag, lock in last year's pricing, and the technician already knows your system's quirks—where the blow-out port is, which zone has the drip line, and how many heads need marking.
- •Do not skip zones that seem dry: Drip zones, bubbler zones, and low-volume zones all hold water in their poly tubing and emitters. They need to be cycled during the blow-out just like spray zones. Missing one usually means a spring discovery of split tubing and replaced emitters.
- •Replace flags that disappear: Check your marker flags every few weeks through the winter. Wind, plows, and kids on sleds knock them over. A head without a flag is a head that will be destroyed. Buy 50 flags at a home center for $8 and keep extras in the garage.
- •Note any problem zones for spring: If a zone did not blow out cleanly—heads that did not pop up, valves that did not open—write that down on the receipt. Those are repair items for the spring startup appointment. Tracking them now prevents a surprise dry spot in July.
Frequently Asked Questions
Can I winterize my sprinkler system myself?
Technically yes, but most homeowners should hire a professional. The core problem is compressor capacity. Residential pancake and hot-dog compressors deliver only 2 to 6 CFM, which is nowhere near enough to push water out of 1-inch buried lines that may run 100 feet or more. You need 80 to 200 CFM at 40 to 80 PSI, which requires a tow-behind or large stationary compressor. Professional blow-outs run $75 to $150 for a typical residential system. Compressor rental for DIY runs $60 to $120 per day, and running too little air for too long can actually damage heads by overheating them without moving water. For most people the math favors hiring it out.
When should I schedule the winterization?
Schedule the blow-out 2 to 3 weeks before the first hard freeze of the season. In the northern United States this typically falls in mid-October, so book the appointment in late September to lock in a date. Irrigation companies fill their calendars quickly in October and a last-minute call after a freeze warning may mean no availability for two weeks. Water left in the system below 32F can crack PVC laterals, destroy backflow preventers, and split brass valves, so do not push the date in hopes of squeezing in a few more waterings.
Do I really need to mark my sprinkler heads with flags?
Yes, especially along driveways, sidewalks, and any route a snowplow uses. A plow blade catches a pop-up sprinkler head invisibly buried under snow and rips it cleanly out of the ground, often breaking the underlying riser and lateral pipe. Replacement is $75 to $200 per head plus labor, and if the plow tore the pipe you cannot repair it until spring thaw. Brightly colored marker flags cost a dollar each, push into the ground in seconds, and prevent the most expensive and preventable failure in any winterized system. Mark the backflow preventer too—a plow or someone walking in deep snow can easily damage an exposed valve assembly.
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