Do you need to winterize your sprinkler system in Fairfield, CA?

Most Fairfield sprinkler systems don't need to be winterized the way they are in snow country. The pipe under your lawn is the safer part of the system. The parts that can freeze are the ones standing in the open air: the backflow preventer, the riser that feeds it and any pipe or valve above the soil. Those need a few minutes of attention before the first clear, cold night.

Search "winterize sprinkler system" and almost every answer is written for Colorado or Michigan, with compressors, blowout fittings and a deadline before the ground freezes. That advice doesn't fit a yard in Fairfield.

Does it actually freeze in Fairfield?

Yes, on some clear winter nights. In December 2021, NBC Bay Area reported a National Weather Service freeze watch for the Fairfield and Suisun City areas, with lows in the upper 20s outside city limits and about 30 degrees inside them. The report warned that the cold could "possibly damage unprotected outdoor plumbing."

The University of California's pest management program (UC IPM) explains when this happens: frost forms as heat escapes into the sky, "especially during cool, clear nights." In practice that means the still, starry nights after a winter storm has cleared out, not the rainy ones.

Do I need to blow out my sprinklers in Fairfield?

Usually not. Texas A&M's School of Irrigation describes the blowout as the method for places with "extreme and/or prolonged freezing conditions" where "the ground will freeze down to the buried pipelines." A clear night near 30 degrees chills the air and the surface. That is a different problem from weeks of frozen ground.

A blowout also carries its own risk. Rain Bird's winterizing page calls compressed air a safety concern and recommends a local irrigation specialist rather than doing it yourself. If someone offers you a "winter blowout" in Fairfield, ask what it protects that wrapping the above-ground parts wouldn't.

Which parts of a sprinkler system can freeze here?

Anything above the soil. Rain Bird's advice is to "insulate backflow preventers and valves if they are above ground." In most Fairfield yards that list is short:

• The backflow preventer. The brass assembly, often near the front hose bib or the corner of the house, that stops lawn water from flowing back into the drinking water.
• The supply riser. The pipe that comes up out of the ground to feed the backflow preventer and drops back down to the valves.
• Exposed PVC. Pipe run along a wall, a fence or a raised bed, where it never got buried.
• Above-ground valves. Anti-siphon valves that stand on a riser instead of sitting in a box.

How do I protect a backflow preventer from freezing?

Wrap it before a forecast freeze, and leave its openings clear. Rain Bird's page adds a warning people miss: "Be sure not to block the air vents and drain outlets on backflow preventers." In practice that means a foam pipe sleeve on the riser and an insulated cover over the brass body, fitted so the air vents and drain outlets stay open. Take the cover off when the day warms up.

Texas A&M's steps for mild freezes go one further: turn off the irrigation supply at the isolation valve, insulate exposed PVC, and drain the above-ground parts such as the backflow assembly. Draining is a reasonable step if you're leaving the system off for the season. If you aren't sure which valve is which, or the assembly has test fittings you've never opened, leave it pressurized and wrapped instead. A cracked brass body is a bigger job than a night of insulation.

Should I turn my sprinkler controller off for the winter?

Put it in rain mode rather than unplugging it. Rain Bird explains that rain mode "simply shuts off the signals to the valves" while the clock and your program stay saved. Cutting power to the controller does the same thing, but you'll have to reset the time and every setting in spring.

Before you switch it off, step the schedule down. Our post on how much to cut back sprinklers in October has the University of California's month-by-month numbers for inland valley lawns. Once steady rain arrives, rain mode carries you through to spring. In a dry spell, switch it back on for a week or two.

A controller that does this on its own costs you less attention. The Solano County Water Agency rebates 50 percent of a WaterSense labelled weather-based controller, up to $300 for a home, and has a rain sensor rebate of up to $50. The rebate finder shows which programs your address qualifies for. If your current timer keeps losing its program or has no rain setting, look at sprinkler controller replacement before the spring startup.

Should I water the yard before a freeze?

If the soil is dry, yes, a few days ahead. UC IPM advises to "irrigate dry topsoil at least 3 days before the cold weather to increase the soil's ability to retain heat." Moist soil holds more warmth around roots than dry soil. In a normal Fairfield winter, rain has usually done this for you. In a dry January, one deep run on the beds a few days before a forecast freeze helps tender shrubs.

UC IPM also notes that frost damage on plants often doesn't show "until days after a freeze," and says not to prune damaged growth until you're sure what is dead. Leave the brown tips on until new growth appears in spring.

What should I check when the sprinklers come back on?

Run every zone once and watch it. A fitting that cracked in a cold snap usually shows itself the first time the system is under pressure again: a wet spot by the backflow preventer, a hiss at the riser or a zone that suddenly runs weak. Water pooling where the ground has been dry for days, or a jump on the water bill, points to a leak below ground. That calls for irrigation leak detection and repair rather than more digging in the wrong place.

One of our Google reviewers, Jennifer, wrote that the crew "checked our sprinklers and found a broken one we didn't know about." That's the point of a spring check. Our sprinkler system diagnostic works through the controller, wiring, valves, pipe and heads in order and runs every zone.

Before the first cold night

Walk the outside of the house and find every piece of irrigation pipe or brass above the soil. Write down where the backflow preventer and its shutoff valve are, and put a foam sleeve and a cover somewhere you can find them on a cold December evening. If you'd rather hand the whole system off, our Fairfield lawn, sprinkler and lighting page shows how we look after yards in town through the year.