When should you winterize your sprinkler system?
Under your lawn right now, a few hundred feet of thin plastic pipe is standing full of water. Not residual damp. Actual water, in the pipe and in the brass backflow preventer above it, waiting for one night cold enough to turn that water into something that splits pipe open.
Once a year, before the first hard freeze, shut off the water and blow every zone out with compressed air. For most of the country that puts the deadline in October.
Budget about 30 minutes:
- Shut off the main irrigation water supply
- Connect an air compressor rated 20 to 25 CFM, set below 50 PSI for PVC pipe or 80 PSI for poly
- Starting with the zone furthest from the compressor, run each zone until only a fine mist leaves the heads
- Close all the manual drain valves
- Insulate the backflow preventer and any above-ground valve boxes
Then one startup in spring, plus a short walk-through each month during the watering season. That’s the year.
The damage happens where you can’t see it
Water left in an irrigation line freezes, expands, and splits whatever is holding it: pipe, fitting, or the body of a zone valve. All of it sits underground.
That is what separates this from a burst hose bib. No stain on the ceiling, no puddle in the basement. The system looks the same in April as it did in October, right up until you turn the water on and a zone geysers. The repair is an excavation, which is why the bill typically runs $500 to $2,000 or more.
Pressure is the part people get wrong
Too little air and water stays in the low spots. Too much and you crack the pipe you were trying to protect, with your own compressor rather than the weather. Stop each zone the moment the spray thins to mist; a minute or two is the whole window, and running a dry zone longer buys you nothing.
If your winters never drop below freezing, skip the blowout and keep the seasonal habits below.
Spring is the other half
Around April, reverse it. Confirm every manual drain valve is closed, then open the main irrigation valve slowly, a quarter turn at a time over a minute or two. Opening it fast sends a pressure wave down dry pipe. That’s water hammer, and it does the damage you spent October avoiding.
Then run each zone and walk the yard reading the spray. A geyser means a broken head, misting means pressure is too high, a dry patch means a clogged nozzle, and flooding means a cracked line.
Three habits for the watering season
- Walk the yard with the zones running once a month, watching for tilted or buried heads, heads blocked by plants, and soggy ground when the system is off
- Clean the heads and filter screens every six months, or every three if you run drip zones for beds and planters
- Update the controller schedule every three months: cut run times 25 to 50 percent in fall, start between 4 and 6 a.m., confirm the rain sensor is active
The monthly walk earns its place because an underground leak shows nothing above ground until it shows something expensive. Wet ground with the system off is the tell.
The test you may owe your water utility
A backflow preventer keeps fertilizer and stagnant irrigation water out of your drinking supply, and it usually comes with a legal obligation attached. Most jurisdictions require a certified tester to check it every year or two, and skipping that can mean a fine or a shut-off notice. Your water utility usually keeps the list of testers, and spring is the time to book one.
How long does a sprinkler system last?
About 20 years. Looked after, closer to 25. Neglected, around 12, which is also where the failure window opens on a well-kept system.
Thirty minutes with a compressor, once, in the right month. Everything that makes irrigation repairs expensive happens underground, in winter, to a system nobody is looking at.