How to Winterize a Sprinkler System

In cold climates, any water left in sprinkler lines, valves and heads can freeze, expand and split pipes. A spring repair bill for cracked lines is far bigger than the cost of winterizing in the fall.

When to winterize

Before the first hard freeze in your area, usually October or early November across the northern states. Once the lawn goes dormant, it no longer needs regular watering anyway.

Step 1: Shut off the water

Find the main shutoff valve for the irrigation system, usually in the basement or a valve box near the water meter, and turn it off. Insulate it if it is in an unheated space.

Step 2: Turn off the controller

Set the timer to rain or off mode so it does not try to run the valves. Many controllers keep their programs, so you will not have to reset them in spring.

Step 3: Drain the water

Manual drain

Some systems have manual drain valves at the low points. Open them to let water run out, then close them.

Automatic drain

Some systems have valves that open on their own when pressure drops. Turn off the water and briefly run a zone to release pressure.

Compressed air blowout

The most thorough method: compressed air pushes the water out of each zone one at a time. It is common in areas with hard freezes.

Blowouts are best done by a pro. Too much pressure can damage pipes and heads, the air must never be blown through the backflow preventer, and compressed air is a serious safety hazard. Always wear eye protection and keep people away from sprinkler heads during a blowout.

Step 4: Protect the backflow preventer

The backflow device is usually above ground and very vulnerable to freezing. Drain it as directed, and wrap it with an insulated cover made for backflow devices.

Spring startup

• Close all drain valves.
• Open the main valve slowly to avoid a pressure surge.
• Run each zone and check for broken heads and leaks.

Frequently asked questions

Do I need to winterize if winters are mild?

In areas with only light, short freezes, insulating the backflow preventer and exposed pipes may be enough. Ask a local pro what is normal where you live.

Can I use a shop air compressor?

Small compressors usually cannot move enough air volume to clear lines properly. Most homeowners hire a pro for a blowout.

Post your sprinkler winterization job and get bids from local irrigation pros.