Winterization is the necessary process of preparing an irrigation system for winter in regions that experience freezing temperatures. Water expands by nine percent when it freezes, generating immense pressure that cracks plastic pipes, fittings, and delicate components like backflow preventers. Failure to remove all standing water before the first sustained hard freeze leads to catastrophic damage and costly repairs when the system is reactivated in the spring.
Determining the Optimal Shutdown Window
Timing the shutdown balances protecting the system from ice and ensuring the landscape receives adequate water until the growing season ends. The most important factor is the arrival of sustained freezing temperatures, not just a brief overnight dip below 32°F. A simple frost, where air temperatures briefly drop to freezing, rarely affects underground lines because the earth acts as a significant thermal insulator.
Underground irrigation pipes are primarily at risk when the air temperature remains consistently below 28°F for multiple days, which allows the frost line to penetrate the soil deeply enough to reach the buried lines. Soil holds heat and cools much more slowly than the air, meaning a single cold night is insufficient to freeze water in pipes typically buried between eight and twelve inches deep. The system should be turned off only after the landscape has gone dormant and no longer requires regular deep watering.
The precise timing varies drastically across different climate zones, making it necessary to consult local historical data for the average first hard freeze. In northern states and high-elevation areas, winterization may be necessary as early as late September or early October. In transition zones, the window often extends into late November or early December. Homeowners should look for historical weather patterns that predict when the temperature will stay below the freezing point for 24 to 48 hours consecutively.
Essential Steps for System Winterization
Once the optimal time is determined, the mechanical process of removing all water from the system begins by shutting off the main water supply valve. This primary valve is typically located near the water meter or inside a basement, and closing it prevents new water from entering the irrigation lines. For systems equipped with manual drain valves at low points, opening these allows water to drain naturally through gravity.
The most effective method for clearing the entire system is the “blowout” method, which uses an air compressor to force remaining water out of the pipes and sprinkler heads. This process requires connecting an air hose to a dedicated blowout port located downstream of the main shutoff and backflow prevention device. Professionals use specialized equipment, and homeowners attempting this must exercise extreme caution due to the risk of component damage and personal injury.
For residential systems, the air compressor should be regulated to a safe pressure between 40 and 60 pounds per square inch (PSI), with a maximum ceiling of 80 PSI for rigid PVC pipe. Exceeding this pressure can easily crack fittings, rupture valves, and blow seals out of sprinkler heads, creating extensive damage. The compressor also needs sufficient volume, or Cubic Feet per Minute (CFM), with a capacity of 10 to 20 CFM being suitable for average-sized residential yards.
Draining the Backflow Preventer
The backflow prevention device is the most vulnerable component because it is usually exposed and contains multiple chambers that trap water. After the main water is off, this device must be drained to prevent cracking of the brass or plastic housing. For a common Pressure Vacuum Breaker (PVB), this involves opening the two ball valves and the two small test cocks to release the trapped water. The ball valves should be left in a partially open, 45-degree angle position to allow residual moisture to expand without damaging the valve body.
Post-Shutdown Checks and Component Protection
After the water lines are completely clear, the final steps involve securing the electronic and above-ground components for the winter. Components that remain exposed above ground should be insulated to protect them from direct exposure to cold air. This includes the backflow prevention device, exposed piping, and the main water meter. Insulating covers or foam wraps designed specifically for plumbing fixtures provide a protective thermal layer.
As a final preparatory step, several checks should be performed:
- Turn off the automatic irrigation controller or set it to “Rain” or “Off” mode to prevent accidental activation.
- If the controller uses a backup battery, remove it to prevent corrosion over the extended off-season.
- Document which zones were fully cleared and ensure all valves and fittings are clearly marked to streamline spring startup.
- Disconnect all hoses from outdoor faucets to prevent water inside the hose bibs from freezing and rupturing the supply line.