Denver Water recommends waiting until after the last freeze, typically around May 5, to turn on your sprinkler system.

Wait for the Last Freeze The last freeze typically occurs around May 5^th, so turning on the irrigation system too soon can be risky – especially if it wasn't properly winterized last fall. Deep freezes can cause severe damage to the system, resulting in leaks or even cracked pipes.

Grass in Colorado will begin to go dormant at the end of October and beginning of November. 9NEWS spoke with garden experts who say October is a good time to winterize sprinkler systems, especially once lows begin to drop below freezing at night and lawns require less water with daytime highs in the 60s.

The blowout process is a pretty quick process, typically only taking about 15 – 20 minutes, depending on the number of zones. General steps are as follows: First shut off the water supply to your irrigation system using the master shut off valve. The contractor will remove the backflow valve.