Winterising Your Sprinkler System in Montana

You turned the water off in November and felt responsible about it. Then the snow melted, you went out to start the system, and there was water arcing out of the backflow assembly in a place it was never supposed to be.

That is not bad luck.

Water froze inside your pipes, expanded, and split them. Shutting the supply off does not remove the water already sitting in them, and in Montana that water freezes whether or not you gave it permission. It is the most ordinary failure in the world, and it costs people real money every single spring.

Why leaving water in the lines costs $500 to $2,000

Water expands as it freezes, and it does not care that your pipes are full of it. The expansion splits pipe, breaks valves, and cracks backflow assemblies, and the repairs that follow run $500 to $2,000.

A cracked backflow assembly alone is one of the biggest single line items you can be handed, and it is also the piece most homeowners never think about until the water is already coming out of it, because it sits low and out of sight in a spot most people never look at until something has gone wrong.

That is the entire argument for a blowout: five hundred to two thousand dollars, set against a service call that costs a fraction of it. You already know which number you would rather write the check for, and the whole decision lives in that gap.

The window: early-to-mid October, before the first hard freeze

The freeze arrives on its own schedule. Montana's first hard freeze has nothing to do with the calendar in your head, and in most of the state you are working against early-to-mid October. Our Montana frost dates page lays out the spread for your corner of the state.

Think of it the way you think about a deer fence in June, when nothing has been chewed yet and there is no rush in the world. Nobody hurries a job whose cost is still months away. The whole trick is that the window closes quietly, on a night nobody marks, and the only way to know you missed it is to find out in spring.

No law requires you to winterize your sprinklers. No statute, no fine. This is a physical deadline, not a legal one. And the penalty for missing it is the $500 to $2,000 above. The ground gets hard, the water in your laterals freezes, and the bill shows up in April.

What a blowout reaches, and what it does not

A blowout clears the buried system, and only the buried system. But that is not everything, and assuming it is will surprise you in spring.

What a proper blowout actually involves

Shut off the water supply to the system first, before you touch the compressor. Blow air into a system still connected to the supply and you are pushing water back against pressure. Everything else follows.

Isolate and drain the backflow assembly before the rest of it. This is the expensive part and the part most often skipped. A testable backflow assembly is a precision device, and if you are not sure how to handle yours, that alone is a good reason to have a professional do the blowout.

Connect a properly sized air compressor to the blowout port on the system. A well-built system has one, and if yours does not, that is the first thing to fix.

Run one zone at a time, never all of them together. Blow a zone, shut it, move to the next, and never open every zone at once.

Know what actually clears the line, because pressure is not it. It is air volume, cubic feet per minute, that empties the laterals, not raw pressure. Excess pressure damages valves and the backflow assembly. You are not blasting water out; you are pushing enough air through to carry it out.

Run each zone until it stops throwing water and you see only mist and air. Then shut it and move on, and do not run a zone dry for long: the compressor pushes hot air, and heat is what kills seals and heads.

Treat drip and micro-irrigation as a different job entirely. Do not blast high-pressure air through drip line. Drip zones get drained, handled on a lower-volume setting, or emptied by an auto-drain or a manual drain valve if the system has one. The same blowout that saves your spray zones can wreck your drip zones. The pressure that clears a spray head in a minute can ruin drip tubing that was never built to take it, so the two get handled separately. They are not the same job.

Shut down the controller once the blowout is finished. Set it to off or to the rain position so it does not try to run a dry system all winter.

Drain everything the blowout does not reach. Hose bibs, side hose, any above-ground line, rain barrels. If you have an interior shut-off for an exterior hydrant, close it and drain the stub.

What a blowout is not

• Shutting off the water and calling it done. Water stays in the low points of every lateral and inside the valves. That is exactly where the pipe splits.
• Blasting a high-pressure shop compressor at the system. You can blow the seals and the backflow apart doing that, damaging the very thing you were trying to protect.
• Forgetting the backflow assembly because it is out of sight. It is one of the most expensive things on the property to replace and the easiest to overlook.
• Blowing out a drip zone like a spray zone. Different line, different pressure, different method.
• Doing it in September out of caution, then running the system again in a warm October. If you blow out, the season is over. Do not refill and run it. If a warm stretch has you wanting to keep watering, wait on the blowout and watch the forecast. Our fall lawn care guide covers how to wind the yard down once you pull the plug.

What it costs, versus what a split costs

Nationally, a sprinkler blowout averages about $93, in a range of $56 to $137, plus $10 to $20 per additional zone. Those are national figures, and Montana is not the national average. Montana trade labor runs roughly 10 to 20 percent above the national average, and about 20 percent or more in Bozeman. The Bureau of Labor Statistics puts the median wage for landscaping and groundskeeping in Montana at $45,350 against $39,150 nationally, and $47,320 in Bozeman. A Montana blowout runs above the national average, then, and a multi-zone yard costs more on top of that. Do the arithmetic on a three-zone system. Even at the high end of the national range plus two extra zones, and even after the Montana premium, you are still comfortably under what it costs to replace a split line or a cracked backflow assembly. Against $500 to $2,000, it is not close. It is a strange thing to price an afternoon of fall work against an excavation in the spring, and yet that is the comparison sitting in front of you every single year. For a fuller picture of state pricing, see our Montana landscaping cost guide.

"Just leave it running" is not a workaround

Some homeowners reason that if the system keeps running, the water never sits still long enough to freeze. It does not work here. Bozeman's watering restrictions are permanent and year-round: sprinklers are capped at three days per week, even addresses Tuesday, Thursday and Saturday, odd addresses Wednesday, Friday and Sunday. But you cannot run it as a freeze defence, because you cannot run it all winter to begin with. The reasoning sounds airtight until you remember that the restriction is not a seasonal one you can wait out, because the same schedule holds in July that holds in January. Our watering and irrigation guide covers how to manage water on a Montana lot.

If you miss the window

If the ground has not frozen and the system has not frozen, you can still have it blown out.

Late is better than never.

Do not run a frozen system to "test" it. That is how a small crack becomes a flood. The system you are tempted to test is the one already holding water that has nowhere to go when it expands, and the test is what lets it out.

If something has already frozen, the damage shows up in spring: a geyser at the backflow assembly, a valve that will not hold, a zone that loses pressure, or water at the manifold. Look for those at startup rather than waiting for the ground to heave. Our spring cleanup walkthrough is a good place to run those checks.

Call a professional. The repair bill is the thing you are trying to avoid, and a thaw-and-drain done wrong costs more than the blowout ever would have. The crack you catch and repair in October is a small bill, and the crack you leave sitting in the ground until April is a much larger one.

For next year: the reason to schedule early is not tidiness. Blowout crews book out and compress into the same two weeks as everyone else, so the last week of the window is when the people who waited get told no.

Frequently asked questions

When should I winterize my sprinkler system in Montana?

Early-to-mid October, before the first hard freeze. Not a legal deadline, but a physical one. The freeze does not wait for you to be ready.

How much does a sprinkler blowout cost in Montana?

Nationally a blowout averages about $93, in a range of $56 to $137, plus $10 to $20 per additional zone. Montana labor runs 10 to 20 percent above the national average, and 20 percent or more in Bozeman, so expect to pay above those figures.

Can I winterize my sprinklers myself?

You can, with the right compressor and a system that has a blowout port. The risk is the backflow assembly, a precision device and one of the most expensive things on the property. If you are unsure how to handle yours, hire it out.

What happens if I don't blow out my sprinklers?

Water freezes in the laterals and valves, expands, and splits pipe and cracks the backflow assembly. Repairs run $500 to $2,000.

Is it too late to winterize my sprinklers?

If the ground has not frozen and the system has not frozen, no. Have it blown out. Late beats April.

A last word

If you are thinking about cutting down the irrigation you have to winterize in the first place, xeriscaping in Montana is worth a look. Fewer zones is fewer things that can split.

Nobody fails at this because they did not care. They fail because the deadline is invisible and the consequence is a season away. Shut the water off if that helps you sleep, then get the system blown out before the ground does the work for you, and check the backflow.

If you would rather hand it to someone, our Find a Pro hub is the place to start.

Not sure what will grow where you are? Find your Montana growing region.