How to Winterize an In-Ground Sprinkler System Before a Freeze

An in-ground sprinkler head and an above-ground backflow preventer beside a suburban home lawn in fall.

Key Takeaways

Shut off the irrigation water supply and turn off the controller before freezing weather arrives.
Drain water from the pipes and above-ground components using the method your system supports.
Protect an above-ground backflow assembly carefully; its valves and test cocks may need to remain partly open while it drains.
Use compressed air only when you know the system’s requirements; never blow out a zone a second time after it is dry.

Table of Contents

When should you winterize an in-ground sprinkler system?
What to do before draining the sprinkler lines
How to drain a system with manual or automatic drains
When is compressed-air blowout appropriate?
How to protect the backflow preventer from freezing
Which winterizing method fits your situation?
Common winterizing mistakes to avoid
Spring restart: what to check before watering
Frequently Asked Questions
Key points to remember

To winterize an in-ground sprinkler system before a freeze, stop automatic watering, shut off its water supply, and remove water from the lines and exposed components. The right draining method depends on whether the system has manual or automatic drains or requires a compressed-air blowout. Water left in components can freeze, expand, and crack pipes, valves, fittings, or a backflow assembly.

When should you winterize an in-ground sprinkler system?

Winterize the system before freezing temperatures arrive in your area, rather than waiting for the first hard freeze. Bow Mar Water and Sanitation District advises customers to shut off and winterize sprinkler systems before the season’s first freeze, and Texas A&M’s School of Irrigation explains that freezing water can expand and damage irrigation components.

Use your local forecast as a prompt to plan, but do not treat one mild night as proof that the season is over. If you are shutting down early, Bow Mar Water and Sanitation District says that doing so a little earlier than normal in fall should not harm lawn health. The practical goal is to finish draining before water in the system is exposed to freezing conditions.

What to do before draining the sprinkler lines

Start by identifying the irrigation shutoff, controller, backflow preventer, and the drain points or valve boxes. The backflow preventer is the assembly that helps keep irrigation water from flowing back into the household water supply; its exposed parts may need separate attention from the buried sprinkler lines.

Turn off the controller. Bow Mar Water and Sanitation District recommends turning off the timer or automatic controller so it cannot start a watering cycle during winter.
Shut off irrigation water. Texas A&M’s School of Irrigation recommends closing the irrigation supply near the water meter or backflow assembly, where many systems have an isolation valve.
Locate the drainage method. Check for manual drain valves, automatic drains, or a system designed for blowout. A controller can activate zones, but it does not by itself remove water from every part of a system.
Identify exposed equipment. Note above-ground piping and the backflow assembly. Texas A&M recommends insulating exposed PVC pipe and draining above-ground irrigation components for light to mild freezing events.

Do not assume every in-ground system has the same layout. Sunday’s basic guidance includes shutting off the main valve and running a sprinkler head to drain water, while other systems use dedicated drains or a blowout. Match the method to the installed equipment instead of combining steps at random.

How to drain a system with manual or automatic drains

If your system has manual drain valves, open the designated drains and let the water leave the lines. LawnStarter describes opening low-point drain valves one at a time and allowing each to drain before moving to the next; the low point matters because water collects where a line slopes downward.

Close the irrigation water supply and turn off the controller.
Open the system’s manual drain valves according to their locations and layout.
Let each section drain before closing or moving on, following the equipment’s instructions.
If the system has automatic drains, use the system’s intended shutdown procedure and verify exposed components are also drained.

Some systems may allow water to drain by opening a sprinkler head, as Sunday describes. That is a simple option only when it suits the system; one head should not be assumed to empty every branch, valve, or above-ground assembly. If water remains trapped in a section, the freeze risk remains there too.

Keep track of which drains you opened and whether you closed them afterward. A short checklist helps prevent a spring startup with an overlooked open drain or a backflow test cock still in the wrong position.

When is compressed-air blowout appropriate?

A blowout uses compressed air to push water out through the irrigation zones. It is not the same as draining through valves, and the Colorado State University Extension warns that once a zone has been blown out, you should avoid blowing it out again: air moving through dry pipes creates friction and heat that could damage them.

Because the correct setup depends on the system and compressor, do not guess at operating pressure or improvise a connection. Follow the equipment’s instructions and use a qualified irrigation professional if you cannot confirm the required procedure. Colorado State University Extension notes that connecting the compressor airline to a metal fitting rather than PVC helps dissipate some heat during blowout.

Do not repeat a blowout on a zone that is already dry.
Do not treat the compressor as a substitute for separately draining and protecting the backflow assembly.
Do not guess at a pressure setting; use the system’s requirements.

For a homeowner unfamiliar with the system, a professional blowout is the more cautious choice. Someone who already knows the zone layout and the equipment’s blowout requirements can follow that procedure without repeating dry zones or overlooking exposed components.

How to protect the backflow preventer from freezing

The backflow preventer often needs its own winterizing steps because it sits above ground and can retain water. Colorado State University Extension describes draining the assembly and leaving its isolation ball valves approximately 45 degrees open for winter. Its instructions also call for opening test cocks during draining and closing them before spring startup if they were left open.

The Colorado State University Extension procedure is specific to the assembly it describes: it includes draining water upstream, opening test cocks in the first check zone, and removing the check cap, spring, and disk holder to drain the downstream zone before reassembly. Because backflow designs differ, do not remove parts from an unfamiliar assembly based only on a general description. Use the instructions for the installed device.

Texas A&M’s School of Irrigation recommends draining above-ground irrigation components and insulating exposed PVC pipes. Insulation is additional protection, not a replacement for removing water: a wrapped component can still be vulnerable if water remains trapped inside it.

Which winterizing method fits your situation?

Choose the method your system was designed to use. The comparison below helps narrow the next step, but it does not replace the manufacturer’s instructions for a particular controller, drain, or backflow assembly.

System or situation	Practical approach	What to watch
Manual drain valves are installed	Shut off supply and open the designated drains	Drain each relevant section and address above-ground components separately
Automatic drains are installed	Follow the system’s shutdown procedure	Do not assume automatic drains empty every component
System requires compressed air	Follow the system-specific blowout procedure	Avoid guessed pressure and do not blow out a dry zone again
Backflow assembly is above ground	Drain and protect it using its device instructions	Valve and test-cock positions matter for draining and spring startup

If you are new to the home, first locate the irrigation shutoff and identify the backflow device before choosing a method. If you have winterized the system before, use your notes to confirm the same drains and controller settings still apply; a replacement controller or plumbing change can alter the process.

Common winterizing mistakes to avoid

A frequent mistake is turning off the controller but leaving the water supply on. The controller setting prevents scheduled operation, while closing the irrigation supply stops new water from entering the system; they address different parts of the shutdown.

Draining only the sprinkler heads: water may remain in lines, valves, or exposed equipment. Identify all system sections and their drainage method.
Forgetting the backflow assembly: it can retain water even after the landscape zones are drained.
Repeating a blowout: Colorado State University Extension cautions that air through dry piping creates friction and heat that can cause damage.
Leaving the controller active: an automatic schedule can run after the system has been prepared for winter.
Relying on insulation alone: Texas A&M’s guidance pairs insulation for exposed pipe with draining above-ground components.

Spring restart: what to check before watering

Before restoring irrigation, review the winter positions of the valves and test cocks. Colorado State University Extension specifically says to close PVB test cocks before turning the system on in spring if they were left open during winter draining.

Open the water supply and restart the system according to its equipment instructions, then check each zone for leaks or components that do not operate as expected. A slow, deliberate startup makes it easier to notice a problem before an automatic schedule resumes. If a backflow component was disassembled for draining, confirm it has been reassembled as instructed before running the system.

Frequently Asked Questions

Can I winterize an in-ground sprinkler system by turning off the water?

Turning off the supply is necessary, but it does not necessarily remove water already in the pipes or backflow assembly. Drain the system using its manual drains, automatic drains, or appropriate blowout method.

Do I need to turn off the sprinkler controller?

Yes. Bow Mar Water and Sanitation District recommends turning off the timer or automatic controller to prevent it from running during winter. This is separate from shutting off the irrigation water supply.

Can I use a sprinkler head to drain the system?

Sunday describes running a sprinkler head after shutting off the main valve as a basic draining step. It may not empty every section or above-ground component, so check the system layout and its intended drainage method.

Should I blow out a zone twice to make sure it is dry?

No. Colorado State University Extension warns against blowing out a zone again once it is dry because compressed air moving through dry pipes creates friction and heat that could cause damage.

What should I do with the backflow preventer in winter?

Drain it and follow the instructions for that specific assembly. Colorado State University Extension describes leaving isolation ball valves about 45 degrees open during winter and closing PVB test cocks before spring startup if they were left open.

Key points to remember

Finish winterizing before freezing temperatures reach your area.
Turn off both the controller and the irrigation water supply.
Use the drainage method built for your system and protect exposed components separately.
Follow device-specific backflow instructions, and do not repeat a blowout on a dry zone.

Valve positions, controller procedures, and blowout requirements depend on the installed equipment. Check the system and backflow assembly instructions before shutdown and again before spring startup.

References

Information in this post was checked as of September 2026. Policies and prices may change, so please verify important details with official sources.

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