Irrigation Winterization & Spring Startup: The Complete Commercial Checklist

Why Winterization Matters for Commercial Systems

Water expands roughly 9% when it freezes. In a pressurized irrigation system, that expansion has nowhere to go. The result is cracked mainlines, split valve bodies, shattered backflow preventers, and blown-out pump seals. On a residential system, a freeze break might cost a few hundred dollars. On a commercial property or golf course, the numbers are different.

A burst 4" PVC mainline under a parking lot can cost $8,000-$15,000 to excavate and repair. A cracked RPZ backflow assembly runs $2,000-$5,000 to replace and recertify. Golf course pump stations are the most vulnerable of all: a freeze-damaged pump, VFD, or pressure tank can exceed $20,000 in parts and labor, plus lost revenue from course closure.

The insurance claim data tells the story. Freeze damage accounts for the single largest category of commercial irrigation repair costs in northern climates. And nearly all of it is preventable with a systematic shutdown procedure.

The inverse is also true: a rushed or incomplete spring startup causes its own damage. Water hammer from rapid pressurization cracks fittings. Debris left in valve boxes jams diaphragms. Heads displaced by snowplows go unnoticed for weeks. A proper startup is not just turning the water back on. It's a full system recommissioning.

Part 1: Fall Winterization Checklist

1 Audit Before You Shut Down

Run a complete system check before winterization, not after. Walk every zone. Record broken heads, leaking valves, low-pressure zones, and any areas where coverage has degraded. This is the cheapest time to document issues because the system is still operational and you can observe performance under pressure.

• Run each zone and note broken, tilted, or sunken heads
• Record valve box locations that are flooded or hard to access
• Flag any zones with noticeably low pressure or poor coverage
• Note mainline leak locations (wet spots, erosion)
• Document everything with photos; your spring crew may be different people

This audit becomes your spring repair punch list. Without it, you'll rediscover the same problems in April and lose weeks of the growing season waiting for parts and labor.

2 Shut Off the Water Supply

Close the main shutoff valve completely. For properties fed by a pump station, follow the manufacturer's shutdown procedure. This typically involves running the pump down to zero pressure, closing suction and discharge valves, and draining the pump housing.

• Close the main irrigation shutoff valve
• For pump stations: follow manufacturer shutdown sequence
• Drain the pump house if unheated (pump casing, pressure tanks, filters)
• Disconnect and drain any booster pumps
• If using a lake or pond intake, pull the foot valve above the ice line or mark its location

3 Drain the Backflow Preventer

Backflow preventers (RPZ, DCVA, PVB) are the most freeze-vulnerable component in the system because they sit above ground and hold water in their bodies year-round. A cracked backflow assembly doesn't just cost money to replace; it can contaminate the potable water supply until it's fixed.

• Close both isolation valves (upstream and downstream)
• Open all test cocks to drain the body
• For RPZ assemblies: open the relief valve drain
• Leave test cocks open at a 45-degree angle through winter
• Schedule annual backflow test before or during winterization (required by most local codes)

If your jurisdiction requires an annual backflow test, combining it with winterization saves a truck roll. Many backflow testers will test and winterize in the same visit.

4 Blow Out the Lines (Compressed Air)

This is the most critical step and the one most often done incorrectly. The goal is to push all standing water out of every lateral line, mainline, and fitting. Incomplete blowouts leave water in low spots and fittings, exactly the places that crack.

• Connect compressor to the mainline via a blowout port or backflow connection
• Open one zone at a time. Never blow with all valves closed
• Start with the zone farthest from the compressor
• Blow each zone for 2-3 minutes until no water is visible at the heads
• Make two passes per zone (let pressure rebuild between passes)
• Watch pressure carefully. Never exceed maximum PSI ratings
• After all zones, blow out the mainline separately if it has a drain point

5 Drain Valves and Low Points

Compressed air won't reach every low point in the system. Manual drain valves exist for a reason. Use them.

• Open manual drain valves at all low points in the mainline
• Drain any above-ground piping (risers, connections to buildings)
• Remove and store rain sensors, flow sensors, and any other above-ground instruments that hold water
• Drain wire runs in conduit if they trap water (common with direct-burial splices)
• Leave manual drain valves cracked open through winter

6 Controller Settings

Turning off the controller sounds simple, but there's a wrong way to do it. Disabling individual programs leaves the controller in a state where a power glitch or accidental button press can restart irrigation in January.

• Set the controller to "off" or "rain" mode (not just disable programs)
• For smart controllers: switch to winter/monitoring mode to maintain connectivity and sensor logging
• Replace battery backups (9V or lithium); cold weather drains batteries faster
• Record all program settings before clearing (photo the screen or export config)
• If controller is in an unheated enclosure, verify it's rated for the expected low temperatures

7 Mark and Protect

Every winter, snow removal crews destroy sprinkler heads, valve boxes, and backflow assemblies because they can't see them under the snow. This is entirely preventable.

• Flag all heads along snow removal paths with tall fiberglass markers
• Mark valve boxes, especially those near parking lots and driveways
• Cover backflow assemblies with insulated pouches or enclosures
• Wrap exposed piping in unheated spaces with pipe insulation or heat tape
• Photograph all marker locations for the snow removal crew's reference
• Communicate head and valve locations to the snow removal contractor directly

Part 2: Spring Startup Checklist

1 Visual Inspection

Walk the entire system before turning on any water. This is non-negotiable. You're looking for damage that occurred over the winter, and there's almost always something.

• Walk every zone looking for frost-heaved heads, displaced markers, and grade changes
• Check for snowplow damage: sheared heads, crushed valve boxes, displaced backflow assemblies
• Open all valve boxes and check for standing water, debris, rodent nests, or ice
• Inspect all above-ground piping and connections for visible cracks
• Verify the backflow assembly is intact and hasn't been hit by equipment
• Check the pump house (if applicable) for signs of water damage, rodent damage, or freeze damage
• Cross-reference against your fall audit. Confirm known issues and note new ones

2 Slowly Pressurize the System

This is the step most people rush, and it causes the most startup damage. Opening the main valve quickly sends a pressure wave through the system (water hammer) that can blow fittings, crack elbows, and damage valve diaphragms.

• Close all zone valves before pressurizing
• Open the main shutoff valve slowly, approximately 1/4 turn per minute
• Listen for the sound of running water, which indicates a break somewhere in the mainline
• Watch the pressure gauge: it should climb steadily and hold. A gauge that rises then drops indicates a leak
• Let the system sit at full pressure for 15-30 minutes before activating any zones
• Check the water meter during this hold period. Any movement means a leak

3 Backflow Assembly

The backflow preventer needs to be reassembled and tested before the system is fully operational. In most jurisdictions, annual backflow testing is required by law, and the system cannot legally operate without a current test certificate.

• Close test cocks that were left open for winter drainage
• Reinstall any test cock plugs that were removed
• Open isolation valves slowly (upstream first, then downstream)
• Check for leaks at all connections and the relief valve
• Schedule the annual backflow test with a certified tester
• File the test report with your local water authority as required

4 Zone-by-Zone Activation

Run each zone manually for 2-3 minutes and inspect every head. This is time-consuming on a large system, but there is no shortcut. Skipping this step means you won't discover broken heads until brown spots appear weeks later.

• Activate zones one at a time from the controller (manual mode)
• At each head, check for proper pop-up height and retraction
• Verify correct arc and radius on rotors
• Look for tilted or sunken heads that need releveling
• Check for nozzle clogs (uneven spray, misting, or weak throw)
• Inspect valve boxes for leaks while the zone is running
• Listen for valve chatter or buzzing (indicates diaphragm or solenoid issues)
• Document every issue with location, zone number, and description

5 Check Sensors and Communications

Sensors that sat dormant all winter need to be verified, not assumed operational. A rain sensor with a dead battery or a soil moisture probe with a corroded connection will silently fail, and you won't know until the water bill arrives or the turf dies.

• Test rain sensor function (manually trip and verify controller response)
• Check soil moisture sensor readings against expected values for current conditions
• Verify weather station data (temperature, wind, solar) is transmitting correctly
• Replace batteries in all wireless sensors and transmitters
• Recalibrate soil moisture sensors if readings seem off
• For smart/connected systems: verify cloud connectivity, data sync, and remote access
• Test flow sensor by running a zone and confirming flow readings match expected GPM

6 Update the Controller

Spring startup is when the irrigation schedule should be set fresh for the new season, not restored from last year's settings. Conditions change: new plantings, different water restrictions, updated ET data, and lessons learned from last season.

• Program the irrigation calendar for the new season start date
• Set watering windows to comply with current local water restrictions
• Adjust run times based on spring conditions (typically 50-60% of midsummer values)
• Update seasonal adjustment percentages if the controller supports them
• Verify rain delay and sensor override settings are enabled
• For smart controllers: sync with current weather data and verify forecast integration
• Set alerts/notifications for flow anomalies and sensor faults

7 Pressure and Flow Test

The final verification step. A pressure and flow test at startup establishes your baseline for the season. Any significant deviation from last year's numbers points to a hidden problem: a leak, a partially closed valve, a degraded pump, or a restriction in the line.

• Check static pressure at the point of connection (mainline, no zones running)
• Check operating pressure at the most remote point in the system (farthest zone running)
• Compare both readings to last year's baseline. A drop of more than 5 PSI warrants investigation
• Read the flow meter while running individual zones and compare to expected GPM
• A flow increase suggests a leak; a flow decrease suggests a restriction or partially closed valve
• Record all readings as this season's baseline

When to Call a Professional

A competent grounds crew can handle most of the checklist items above. But some tasks require licensed contractors, specialized equipment, or both.

The cost of hiring a professional for these items is trivial compared to the cost of getting them wrong. A botched compressor blowout can cause $10,000+ in underground damage that doesn't reveal itself until the system is repressurized months later.

Further Reading

• Safety Systems That Prevent Irrigation Disasters — How automated shutoffs and leak detection protect your investment
• How to Read Soil Moisture Sensors — Understand what your sensors are telling you
• Smart Irrigation vs Timers — Why schedule-based irrigation wastes water and money