Blow out your sprinklers before the first hard freeze. In the Denver metro that usually means booking from late September through mid-October. Foothills neighborhoods — Golden, west Arvada, west Lakewood — should go first.
Frost vs. hard freeze
A light frost — a couple of hours right around 32°F — usually won't damage an irrigation system. The water in buried lines is insulated by the soil, and a short dip doesn't freeze much of anything.
A hard freeze is different: generally 28°F or colder for several hours. That's cold enough to freeze the water sitting in the parts of the system that are above ground or close to the surface — especially the backflow preventer, which is usually exposed next to the house. Water expands as it freezes, and brass and PVC crack.
The short version
- Book your blowout before the first forecast hard freeze — not after
- Denver metro: most people book late September through mid-October
- Foothills and higher-elevation neighborhoods freeze earlier — book earlier
- If a hard freeze is in the 3-day forecast and you haven't blown out, wrap the backflow preventer and call
Why Denver timing is tricky
Front Range falls swing hard. It's common to have a 75-degree afternoon followed by a cold front that drops overnight temperatures into the 20s. Waiting for "the last nice weekend" is how people end up with a cracked backflow preventer in April.
There's also very little downside to going a little early. Lawns need much less water in October, and a couple of weeks without irrigation at the end of the season won't hurt established turf.
Timing by area
- Golden and foothills neighborhoods: late September to the first week of October
- West Arvada and west Lakewood: early October
- Thornton, Westminster, Northglenn, Broomfield: late September through mid-October
- Denver, Cherry Creek, Aurora: late September through mid-October
What if a hard freeze is coming and you haven't blown out yet?
Shut off the irrigation supply valve, wrap the backflow preventer with an insulated cover or towels and a plastic bag, and turn the controller off. That buys you time — it doesn't replace a blowout, because water is still sitting in the lines and valves. Then book a blowout or call (720) 818-5569.
What a proper blowout includes
Every zone blown out with compressed air at a regulated pressure until the heads run dry, the backflow preventer drained with its test cocks left partly open, and the controller set to off. See exactly what's included. You don't need to be home.