Waking the system up
Spring Irrigation Startup Denver
Spring System Charging & Winter Damage Checks
Startup is the day your system tells you what winter did. Charge it too fast and you add fresh damage to the old damage. Done right, it's a slow fill, a walk through every zone, and an honest list of what needs fixing before June.
- Late frost sets the date
- Slow fill beats water hammer
- First run finds the damage
- Controller set for May
The calendar is not on your side in April
The urge to fire up the sprinklers hits the first 70-degree Saturday, which around here can happen in March. Resist it. The date that matters is your area's last hard freeze, and along this corridor that runs from roughly April 30 in Denver to about May 5 in Longmont and Erie, May 7 in Boulder and Golden, May 10 in Castle Rock, and as late as May 18 up on the Palmer Divide in Monument.
Charge a system in mid-April and you've put water back into the most freeze-vulnerable plumbing on your property, weeks before the last freeze historically clears. A May snow that snaps tree limbs will also crack a backflow assembly that's sitting full. It's the same failure as a skipped fall blowout, just on the other end of the season.
There's an agronomic argument too. Kentucky bluegrass and fescue lawns come out of dormancy on soil temperature and spring moisture, and a normal Front Range April supplies a fair amount of that for free. Turf that gets soaked in April roots shallow and then struggles in July.
So the practical answer for most of the metro is the first week or two of May, and later than that on the Divide. Watch the ten-day forecast rather than the calendar alone. If a hard overnight low is coming after you've charged the system, shut the isolation valve and drain the backflow again. Ten minutes of work beats the alternative.
Charge it slowly, then walk every zone
Almost all self-inflicted startup damage comes from one mistake: opening the supply valve all the way, all at once. An empty mainline offers no resistance, water accelerates down it, and when that column slams into the first closed zone valve the spike can run several times static pressure. That hammer is what splits fittings, blows bonnets off backflow assemblies, and pops glue joints that were fine all winter.
The fix costs nothing but patience. Crack the indoor isolation valve open maybe a quarter turn and listen. You'll hear the line filling. When the hiss quiets down, meaning the pipe is full and pressure has equalized, open the valve the rest of the way. On a large system that wait is several minutes. Use them.
Once it's charged, run the zones one at a time and actually watch. First-run behavior is messy on purpose: heads spit, air purges, grit that settled over the winter blows through the nozzles. Give each zone two or three minutes and walk it. The zone you skip is the zone with the geyser behind the shed.
Take notes as you go instead of trying to remember. Tilted heads, arcs watering the sidewalk, a body that won't retract, a soft spot that's soggy before the zone has run three minutes. That list becomes your repair scope, and it's much cheaper to hand somebody one list than to call three separate times.
- Close the indoor bleeder cap and confirm the drain is shut
- Turn the backflow ball valves from their 45-degree winter position to fully open, slowly
- Close both test cocks on the assembly
- Crack the isolation valve a quarter turn and wait for the fill to go quiet
- Open the isolation valve fully, then run each zone manually and watch it
- Reset the controller date and time, and replace the backup battery if it has one
What winter left behind, and what it costs
Damage found at startup falls into a few buckets, and they price very differently. Broken heads and sheared risers are the cheap end, quick work in soft turf and more involved in rock beds or under flagstone. Split laterals mean digging, and digging in Front Range clay is what drives that number.
The one to look at first is the brass. A backflow assembly that weeps from a seam, lifts at the bonnet, or won't hold pressure is the single most expensive part on most residential systems, and freeze is what kills it. Get it tested before you spend money elsewhere, because a cracked body is a replacement and that changes your whole budget for the season. Our page on annual testing and freeze damage covers what's rebuildable.
Watch for the delayed failures too. Some freeze cracks hold for a week or two under pressure before they open, so a leak that shows up in late May can still be a January injury. If your water bill jumps and nothing is visibly wrong, run each zone and look for a patch of lawn that's greener and softer than the rest.
A full professional startup, meaning the charge, a zone-by-zone check, and controller programming, commonly lands in the low hundreds along the Front Range, with repairs quoted separately. Bundling the backflow test into that visit usually saves a trip charge. If you're comparing bids, ask whether the startup fee includes adjusting heads and nozzles or whether that's billed as repair time, since that single distinction explains most of the spread between quotes.
- The brass is weeping or the bonnet looks liftedstop and get it tested first. That's the most expensive part on the system.
- One zone geysers and the rest look finethat's a broken head or riser, and it's a contained repair. Note it and move on.
- Several zones are weak at oncelook upstream at the mainline or the pressure source, not at individual heads.
- Nothing runs at all after a good chargecheck the controller, its backup battery, and the master valve before assuming the worst.
Need this handled this week?
Start a quoteProgram it for a Colorado May, not a Missouri June
The default schedules baked into controllers assume a wetter, denser soil and calmer air than we get here. Clay along this corridor takes water slowly, so a single long run mostly produces a stream down the gutter. Cycle and soak fixes that: split a zone's run time into two or three shorter cycles with a gap between them, and the same total water actually gets into the root zone instead of onto the sidewalk.
Slopes make it worse, and this metro has plenty of them. Terraced lots in Golden, Superior, and the west side of Lakewood run off long before flat lots do, and those zones usually want the shortest cycles on the property.
Wind is the other Colorado variable. Afternoon gusts turn a spray zone into a mist zone and carry a real fraction of it somewhere useless. Early morning is the default answer for a reason. And when May is cool and wet, use the seasonal adjust dial rather than leaving a July schedule running, since a system set once in spring and forgotten is how people end up watering through a rainstorm in front of the neighbors.
Once the system is dialed in, the loose ends from startup are worth closing out promptly. Broken heads waste more water than a bad schedule ever will, and our repair walkthrough sorts the symptoms by what's likely behind them. Homeowners in newer northern subdivisions in particular should check zone edges early, since settling soil shifts head heights over the first several seasons.
Start in May, not April. Fill the pipe slowly enough to be boring. Walk every zone once while it runs, write down everything wrong, and fix it in one trip. Then set the controller for clay soil and morning wind. Do those four things and your system's worst day is behind you.
Related work
More sprinklers services
Where we cover
Front Range cities we write for
Questions we actually get
Spring Irrigation Startup: quick answers
How early can I turn my sprinklers on in the spring?
Work from your area's historical last freeze. Denver clears around April 30, most of the metro in the first week of May, Boulder and Golden a bit later, and Monument not until mid-May. Charging earlier puts the backflow assembly at risk from a late cold snap. Lawns rarely need supplemental water in April here anyway.
Why do my heads sputter and spit air on the first run?
That's normal. The lines have been full of air since the fall blowout, and it has to leave through the nozzles. Give each zone a few minutes and the spitting settles. What isn't normal is sputtering that continues past the first couple of cycles, which usually points to a leak drawing air in somewhere along the lateral.
Do I need a professional for spring startup?
Not always. A careful homeowner who opens the valve slowly and walks each zone can handle it. Hand it off when your system has a backflow assembly due for its annual test, when you can't locate the isolation valve, or when the last few seasons ended with repairs. Bundling startup with the test usually saves a separate trip anyway.
Waking the system up this month?
Tell us what your first run turned up and where you are, and we'll help you sort the cheap fixes from the real ones.
Get My Free Quote