Sprinkler winterization uses compressed air to force water out of irrigation lines, heads and valves before freezing weather. Simply draining is not sufficient because water remains trapped in low points, heads and the backflow preventer. In Colorado Springs the work should be done in September, ahead of the typical early-October hard freeze.
Why draining is not enough
Irrigation systems are not installed with a perfect slope back to a drain. Lateral lines follow the ground, which means there are low spots that hold water no matter how long you leave a drain valve open. Sprinkler heads retain water in their bodies. Valve bodies hold water around the diaphragm. And the backflow preventer — the assembly above ground near where the irrigation line leaves the house — has internal chambers that stay full.
Water expands as it freezes. In a buried polyethylene lateral, a small amount of trapped water may split the pipe or simply stretch it. In a brass backflow assembly, it cracks the body. The backflow preventer is typically the most expensive single component in a residential irrigation system and it is the one sitting exposed above ground, which is a poor combination.
What a proper blowout involves
- Shut off the irrigation supply at the valve inside the house, usually in a basement or crawlspace near where the line leaves.
- Open the test cocks and drain the backflow assembly, then leave the ball valves at 45 degrees so any residual water has somewhere to expand.
- Connect the compressor at the blowout port downstream of the backflow device.
- Run one zone at a time, starting with the zone farthest from the compressor, letting air push the water out through the heads.
- Watch each zone until the heads are discharging a fine mist rather than water, then move on. Short cycles, repeated, rather than one long blast.
- Set the controller to off or rain mode, and remove or replace its backup battery.
- Insulate the backflow assembly if it stays installed over winter.
The part people get wrong
Compressor sizing. The instinct is to think in terms of pressure, and that is exactly backwards. Pressure must be kept low — too much will blow the seals out of heads and valves, and plastic fittings do not survive it. What actually pushes water out of a long lateral is volume: cubic feet per minute. A typical portable shop compressor has nowhere near enough CFM to clear a residential zone, so people run it at high pressure to compensate, which is how heads get destroyed.
The other common mistake is running air through the backflow preventer rather than connecting downstream of it. Forcing air backwards through the assembly can damage the internal check valves — the thing you were trying to protect.
This is why most homeowners hire this out, and it is a reasonable thing to hire out. If you do own a large enough compressor, keep pressure conservative, never leave a zone running dry for long, and stay clear of heads while they are discharging.
Everything else outside
Do all of this in the same September pass:
- Disconnect every hose. A hose left attached is the single most common cause of a split frost-free hose bib, and the split is inside the wall where you will not see it until spring.
- Drain and store hoses out of the sun. High-altitude UV destroys them faster than the freezing does.
- Open each hose bib and confirm it drains and stops.
- For non-frost-free bibs, close the interior shutoff and leave the exterior faucet open all winter so the line between them is empty.
- Insulated faucet covers on exposed, wind-hit walls.
- Outdoor kitchens, pool fills, wash-down stations and detached garages — anything on a separate line needs the same treatment and is routinely forgotten.
- Drain and store rain barrels; a full barrel freezes solid and splits.
Timing, specifically
The Colorado Springs area typically sees its first hard freeze in early-to-mid October, but the Front Range does not read the average. An overnight dip well below freezing in late September is entirely ordinary, and it only takes one. Mid-to-late September is the right window: late enough to get the last of the season's watering in, early enough that you are not gambling.
If a freeze is forecast and you have not winterized yet, shut off the irrigation supply, drain what you can, open the backflow test cocks, and disconnect hoses. That is not a substitute for a blowout, but it will get you through a single cold night.
In spring
Bring the system back slowly. Close the test cocks, open the main irrigation valve gradually rather than all at once — a sudden surge into empty pipe causes water hammer that can damage valves and fittings — then run each zone and walk the yard looking for heads that did not survive. Backflow assemblies require periodic testing by a certified tester in many jurisdictions; worth confirming your local requirement.
For indoor plumbing ahead of winter, see our frozen pipe prevention guide and which pipes freeze first. Smith handles plumbing repair, including the hose bibs and interior lines that come out of winter badly, and emergency plumbing when something has already let go.
Frequently asked questions
When should I winterize my sprinkler system in Colorado Springs?
Mid-to-late September is the right window. The first hard freeze in the Colorado Springs area typically arrives in early-to-mid October, but an overnight dip below freezing in late September is common and a single night is enough to crack a backflow preventer. Scheduling in September avoids gambling on the forecast.
Can I just drain my sprinkler system instead of blowing it out?
Draining alone is not sufficient. Irrigation lines follow the contour of the ground, so low points hold water regardless of how long a drain valve stays open, and sprinkler heads, valve bodies and the backflow assembly all retain water internally. Compressed air is what actually clears those.
What size compressor do I need for a sprinkler blowout?
Volume matters, not pressure. Clearing a residential zone requires substantial cubic feet per minute, and a typical portable shop compressor cannot deliver it. People compensate by raising pressure, which blows the seals out of heads and valves. Keep pressure low and use a compressor with adequate CFM, or hire the work out.
What happens if I forget to winterize my sprinklers?
Trapped water expands as it freezes and can split buried lateral lines, crack sprinkler head bodies, damage valve diaphragms and fracture the backflow preventer, which is usually the most expensive component and sits exposed above ground. Damage often stays hidden until the system is pressurised again in spring.