The first hard freeze of the year does not send a warning text. One night the temperature drops to 24 degrees, the water sitting inside your tubing turns to ice, and ice takes up more room than water. By morning a fitting that cost you 80 cents has split down the side, and you will not know until spring when the line sprays like a fountain.
I have replaced more freeze-cracked backflow preventers than I can count, and almost every one was avoidable. The trick is to get the water out before it freezes.
That is what it means to winterize drip irrigation: you drain the water, push out what you cannot drain, and tuck the fragile parts somewhere warm. Do it in an afternoon and you save yourself a scavenger hunt for leaks in April.
Key takeaways
- Water expands when it freezes, so any water trapped in tubing, valves, or a backflow preventer can crack the part.
- Draining by gravity handles most of the water, but low spots need a blowout with air at 40-50 psi.
- Remove and store the parts that crack most: the backflow preventer, filter, pressure regulator, and any timer.
- In mild-winter zones you may only need to insulate, but a single hard freeze still calls for a full drain.
Know your freeze risk before you start
Not every gardener needs the full routine. A “hard freeze” means the air stays at or below about 28 degrees Fahrenheit for a few hours, long enough for standing water to freeze solid inside a pipe.
Here in Tucson we get maybe a handful of those nights a year, so I mostly drain and insulate. If you live somewhere with weeks of sub-freezing weather, you want everything blown out and the delicate parts indoors.
The parts that fail first are the ones that hold a pocket of water and cannot flex. Your backflow preventer (the brass or plastic device that stops dirty water from being sucked back into your drinking supply) is the usual casualty, along with the filter housing and the pressure regulator.
Watch out
A cracked backflow preventer is not just a leak. It can let contaminated water flow back toward your household supply. If yours freezes, replace it before you run the system again, do not try to seal the crack.
Step one: shut off and drain by gravity
Start by closing the valve that feeds your drip system, usually right after the backflow preventer. Then open the end of every zone so water can run out.
Most 1/2 inch mainline tubing has a figure-8 end closure or a screw cap at the far end. Pop those open. If you have flush valves or an end-of-line cap, this is the moment they earn their keep.
- Turn off the water supply to the drip system at the shutoff valve.
- Open the drain or end cap at the lowest point of each zone.
- Open the ends of your 1/2 inch mainlines and let them run until they stop dripping.
- Disconnect any 1/4 inch feeder tubing at the connectors if it sits in a low, water-holding loop.
- Leave the ends open while you move on to the blowout, so trapped air can escape.
Gravity gets you maybe 80 percent of the way. The problem is the low spots, where tubing dips under a path or around a raised bed and holds a puddle no amount of tipping will empty.
Step two: blow out the low spots
This is the part people skip, and it is the part that saves the fittings. You need to push the leftover water out with air.
A small pancake air compressor works fine. Set the regulator low, around 40-50 psi, and never higher than what your tubing is rated for. Drip tubing is thin-walled and does not need much; too much pressure can blow a fitting right off.
Quick tip
Wear eye protection and blow out one zone at a time with its end open. Water and grit come out with real force. Work from the supply end toward the open far end so the air pushes water in one direction.
When I first tried blowing out a system years ago, I cranked the compressor to 90 psi because I figured more air meant a cleaner job. I popped three emitters off a rose bed and spent the next hour hunting for them in the gravel. Low and slow is the whole game.
Let the air run through each zone until only a light mist and then nothing comes out. A few seconds per zone is usually enough on a home system.
What if you do not own a compressor?
A bicycle pump with an adapter can clear short runs, though it is slow going. You can also rent a compressor for around 30 to 40 dollars a day, which is cheaper than one cracked regulator. In a pinch, disconnecting and hand-draining each low loop works too, it just takes patience.
Step three: remove and store the fragile parts
Air will not save a component that holds water in a sealed chamber. Those come off and go inside.
Unscrew the backflow preventer, the filter, the pressure regulator, and unplug any battery timer. Shake out the water, let them dry, and set them on a shelf in the garage or a closet where it stays above freezing.
| Component | Freeze risk | What to do |
|---|---|---|
| Backflow preventer | High (holds water, rigid) | Remove and store indoors |
| Filter and housing | High | Remove, clean screen, store dry |
| Pressure regulator | High | Remove and store indoors |
| 1/2 inch mainline | Medium | Drain and blow out, leave in place |
| 1/4 inch drip line | Low to medium | Blow out, cap ends |
| Battery timer | Medium (electronics) | Remove batteries, store indoors |
Cleaning the filter screen now is smart. A screen caked with mineral scale or algae is one of the most common reasons a system underperforms, and starting fresh in spring beats troubleshooting a weak flow later. If you have run into that before, our notes on backflow and filter problems in drip systems walk through the usual culprits.
A quick end-of-season checklist
Here is the run I do on every winterizing call, start to finish.
- Water supply shut off at the valve
- All zone ends and drain caps opened and drained
- Low spots blown out at 40-50 psi
- Backflow preventer, filter, and regulator removed and stored inside
- Timer batteries pulled, timer stored dry
- Open tubing ends capped loosely to keep out bugs and grit
- Any exposed valve boxes insulated with a towel or foam cover
Good to know
If a mild-winter zone only sees the occasional cold snap, wrapping the aboveground parts with foam pipe insulation or an old towel can carry you through a single 26-degree night. Just watch the forecast, because insulation slows freezing, it does not stop a long cold spell.
Getting ready for spring startup
Winterizing well makes the spring restart easy. When the last frost passes, you reinstall the stored parts, close up the tubing ends, and turn the water on slowly while you walk the lines.
That first slow pressurization is when hidden trouble shows itself. If a line spurts where it should not, you may have missed a low spot, and our guide to finding and fixing a drip mainline leak will get you sorted. If flow is weak or uneven, the broader drip irrigation troubleshooting walkthrough covers the fixes in order.
Most freeze damage traces back to skipped steps, which is worth remembering. If you want to understand the pattern, our rundown of common drip system errors that cause failures puts freeze cracks in context with the other big offenders.
Where to go from here
Winterizing is one of those chores that feels optional right up until it is not. Give it an afternoon this fall, store the fragile parts somewhere warm, and you will spend spring planting instead of patching.
For the science on why frozen pipes split and how cold does its damage, the EPA WaterSense program and your local University of Arizona Cooperative Extension both offer solid regional guidance on timing your shutdown for your climate.
Frequently asked questions
When should I winterize my drip irrigation system?
Do it after your growing season ends but before the first hard freeze, which usually means when overnight lows start dipping toward the high 20s Fahrenheit. Watch your local forecast rather than a fixed calendar date, since freeze timing shifts year to year. If a surprise cold snap hits early, at minimum drain the lines and pull the backflow preventer inside.
Do I really need an air compressor to blow out the lines?
Not always, but it is the most reliable way to clear low spots where water pools and freezes. Gravity draining handles most of the water, and short runs can be cleared with a bicycle pump and adapter. If your tubing has dips under paths or around beds, a compressor set to 40-50 psi is worth renting for about 30 to 40 dollars a day.
What psi is safe for blowing out drip tubing?
Keep it low, around 40-50 psi, and never above what your tubing is rated for. Drip tubing is thin-walled, so high pressure can blow emitters and fittings right off the line. Work one zone at a time with the far end open so the air has somewhere to go.
Can I leave my backflow preventer outside over winter?
It is the part most likely to crack, so I recommend removing it and storing it indoors above freezing. It holds a pocket of water in a rigid brass or plastic body that cannot flex when the water expands. A cracked backflow preventer must be replaced, not patched, because it protects your drinking water supply.
What if I live somewhere with only mild winters?
In a mild-winter zone you may only need to drain the lines and insulate the aboveground parts with foam or a towel. That said, a single hard freeze can still split a fitting, so drain the system and pull the fragile components inside whenever a real cold snap is forecast. Insulation slows freezing but will not protect against a long cold spell.
How do I restart the system in spring?
Reinstall the stored parts, cap the open tubing ends, and turn the water on slowly while you walk every line. That gradual pressurization reveals any leaks or missed low spots before they become a problem. Clean or replace the filter screen at the same time so you start the season with full flow.
