Updated for the 2026 season by the Superior Sprinkler Systems team. We have been winterizing irrigation systems across Loudoun County and Northern Virginia since 1991.
Quick answer: To winterize a sprinkler system, shut off the irrigation water supply, set the controller to off, then clear the water out of every pipe, valve and head before the first hard freeze. In Northern Virginia that usually means late October to late November. Most systems here are best cleared with a compressed air blow-out, done zone by zone at a safe pressure.
Our winters are not as long as they are farther north, but they swing above and below freezing many times. Every hard freeze is another chance for water left in the lines to expand and split something. The damage often goes unnoticed until spring, when the system is turned back on and a zone will not pressurize or water sprays out of the backflow device. Our spring start-up calls are a good record of what gets missed in the fall, and most of those repairs could have been avoided.
Plan to have your system winterized after your last useful watering and before the first hard freeze. In Loudoun and Fairfax counties, that window usually runs from late October through late November. Lawns need very little irrigation once temperatures drop, so there is no real benefit to waiting until the last minute. Booking early also means you are not competing with everyone else who waited for the first cold forecast.
A useful rule of thumb is the hard freeze: temperatures below about 28°F for several hours. That is when water left in lateral lines, valves and the backflow preventer can freeze, expand and split fittings. Once nighttime lows start settling into the low 30s, it is time to get on the schedule rather than wait for the first freeze warning.
The blow-out method uses compressed air to push water out of the pipes, valves and heads. It is the method we use on almost every system we winterize, because it clears water from low spots that draining cannot reach.
Manual draining only works well on systems that were built with drain valves at the low points. If your system has them, the process looks like this:
Draining can leave water in pipe that dips between drain points, and in heads with check valves. If you are not certain every low point has a drain, the blow-out method is the safer choice.
Most irrigation backflow preventers in Northern Virginia are mounted above ground beside the house. That makes them the most exposed part of the system and the part we replace most often after a cold winter. Once the system is cleared, leave the valves and test cocks set so the assembly is empty, and cover it with an insulated pouch or bag. If your backflow preventer is due for its yearly certification, it is easiest to handle that before the system is shut down for the season. See our backflow testing and certification page for details.
If you have the right compressor, know your system layout and are comfortable with the pressure limits, you can winterize your own system. Most homeowners in our area have us do it because the equipment is expensive to own for a once-a-year job and the cost of a mistake shows up in spring. Our certified technicians clear every zone, set the controller for the off season and make a note of any broken parts so they can be fixed before spring. If you are interested, our sprinkler winterization service page explains what is included.
Before the first hard freeze. For most Loudoun County and Fairfax County properties that means scheduling between late October and late November. A single light frost usually does no harm, but several hours below freezing can crack pipes, valves and the backflow preventer.
You can, if you have a compressor that delivers enough air volume, you know where every valve and drain is, and you keep the pressure within safe limits for your pipe. Too much pressure can blow apart fittings and heads, and too little leaves water behind. If you are unsure, a professional blow-out is the safer choice.
Manual draining works on systems built with drain valves at the low points. Most systems in our area are not built that way, so water stays trapped in low sections of pipe and in the heads. A compressed air blow-out clears the lines more completely, which is why it is the method we use.
Water left in the system expands when it freezes. The most common damage we see in spring is a cracked backflow preventer, split pipe, cracked valve bodies and broken heads. Those repairs usually cost more than the winterization would have.
Set it to off or rain mode so it does not try to run zones with the water shut off. Leave it plugged in so it keeps its program and the clock stays correct for spring. Smart controllers can stay connected to WiFi over the winter.
On most homes in Northern Virginia the backflow assembly sits above ground next to the house, which makes it the part most likely to freeze. After the lines are cleared, the isolation valves and test cocks are set so no water is trapped inside, and it helps to cover the assembly with an insulated bag.
Need your system winterized? Request a winterization appointment and our team will get you on the schedule before the first freeze.