How to Winterize Your Sprinkler System: The Fall Blowout Guide

Why do Montana irrigation systems need a fall blowout?

Montana systems need a blowout because water expands roughly nine percent when it freezes, and that expansion has nowhere to go inside a sealed pipe. The result is the same as forgetting a soda can in the freezer: something has to give. Our hard freezes start early and run deep, so any water trapped in below-ground lines, valves, or backflow devices is at risk. A blowout forces compressed air through the system to push that water out before the first hard freeze does the damage for you.

When should you winterize in western Montana?

Aim to blow out the system in fall, before the first sustained hard freeze, which in the Bitterroot Valley and Missoula area often means late September into October. The goal is to beat the freeze, not to squeeze the last week of watering out of your lawn. Watch the overnight forecast as October arrives; once nights start dipping well below freezing, the ground begins to lock up. Scheduling early is wise because the cold can arrive suddenly, and reputable crews book up fast as the season turns.

How far ahead should you book a blowout?

Earlier than feels necessary. Blowouts compress into a few weeks every autumn because everyone in the valley needs the same job done before the same freeze, and the number of crews with a properly sized compressor does not expand to meet that. By the time the first hard frost is in the forecast, the schedule for that week is usually already full.

Getting on the calendar in September for work in October is the comfortable version. It costs nothing to book early and reschedule if autumn runs warm, whereas calling once the forecast turns means taking whatever slot is left. Our sprinkler blowout and winterization schedule fills in roughly that order.

What if a hard freeze is forecast before your appointment?

Shut the irrigation water supply off at the valve and, if your setup allows, open the system's manual drains so gravity takes out what it can. Insulating the backflow assembly helps, since it sits above ground and is usually the most exposed and most expensive component to replace. None of this substitutes for a blowout, but it reduces how much water is sitting in the vulnerable parts.

Then call and say a freeze is coming. A single overnight dip is not the same emergency as a sustained hard freeze, and knowing which one you are facing changes how we prioritise the list. What does not help is leaving the system charged and hoping the forecast is wrong.

Does a larger or commercial system need earlier scheduling?

Yes. More zones mean more time on site, because each zone has to be blown out individually rather than the whole system at once, and a large property may have several controllers, multiple points of connection, or backflow assemblies that need separate attention. That is a longer appointment, and longer appointments are harder to slot in late.

Properties with irrigation running through parking islands and boulevards have a second reason to go early: that work is easier before snow management starts using the same ground. If a site has both, sequencing the irrigation shutdown ahead of the snow season saves revisiting it.

How does a sprinkler blowout actually work?

A blowout uses a properly sized air compressor to push water out of each zone, one at a time. The technician shuts off the water supply, connects the compressor at a fitting, and then opens each zone so the air drives the remaining water through the heads until only a fine mist and then air come out. It is methodical, like clearing each lane of a pool before draining it. Each zone gets its turn at a controlled pressure so the lines empty fully without stress on the components.

Can I just drain the system myself?

Manual or automatic drains help, but in our climate they rarely remove enough water on their own. Low spots, heads, and valves hold pockets of water that gravity drains miss, and those pockets are exactly where freeze cracks start. Just as importantly, using too much air pressure during a DIY blowout can blow seals and crack fittings, trading one problem for another. The right tool sized to your system, used at the right pressure, is what protects the parts you paid to install.

What happens if you skip winterizing?

Skipping the blowout risks cracked pipes, split valves, ruptured backflow devices, and broken heads, and you usually will not discover the damage until you turn the system on in spring. By then a single freeze can have caused repairs across multiple zones, often costing far more than the winterization itself. Worse, freeze damage is entirely preventable and stems from skipped maintenance. An hour or two of work in the fall is cheap insurance against a frustrating, expensive spring.

What should you check in spring before restarting?

When you reactivate in spring, reintroduce water slowly and walk the yard zone by zone. Open the main supply gradually to avoid a pressure surge, then run each zone to check for leaks, geysers, or heads that no longer pop up. Look for soggy spots that hint at a buried break. Catching a small issue at startup is far easier than chasing it mid-summer when your lawn is depending on the system. A professional spring startup pairs naturally with the fall blowout.

Beat the freeze this year. Call HJ Property Care & Tree Service at (406) 493-8300 to schedule a professional fall blowout and protect your irrigation system across Missoula and the Bitterroot Valley.

Would rather have it done for you? Our sprinkler blowout and winterization service covers the whole process before the first hard freeze.

Why does freezing actually split a pipe?

Water expands as it freezes, and it does so with enough force that no common irrigation material contains it. In a buried line the water freezes from the outside inward, so pressure builds in the remaining liquid until something gives — typically the weakest point, which is a fitting, a valve body, or the thin-walled section of a head.

Different materials fail differently. Poly pipe has some give and often survives where a rigid fitting does not, which is why damage frequently shows up at joints rather than mid-run. Brass components such as backflow assemblies split outright, and because they are expensive and code-required, they account for a disproportionate share of the cost of a skipped winterization.

This is also why partial draining is not enough. A line that still holds water at any low point has a freeze risk at that point, and the failure will be found in April by the sound of water running where it should not be.

Does it matter where my water comes from?

It changes what shutdown involves. A system on municipal supply has a clear isolation point and a backflow assembly that needs draining and protecting. A system fed from a well has a pump to consider, and pressure tanks and supply lines that may run through unheated space. A ditch-fed system may already be dry when the ditch stops running, but the delivery lines and any filtration still hold water.

Filtration is a step people forget on well and ditch systems. Filter housings hold water, are often the least freeze-tolerant component in the run, and are cheap to damage and annoying to source mid-spring.

Whichever the source, the sequence is the same in principle: isolate the supply, remove water from the distribution, protect the components that cannot tolerate freezing, and shut down the controller. What differs is where the water hides.

What should I record so next year is easier?

A surprising amount of the cost of irrigation work is discovery. Systems get extended, valves get buried, and the person who installed it moved away. Writing down what you learn at shutdown converts that into a five-minute job next time.

Worth recording: how many zones there are and what each one covers, where the valve boxes are, where the main isolation valve is, where the backflow assembly sits, and the make and model of the controller. Photographs of open valve boxes with the lids off are more useful than notes, and cost nothing.

Add anything unusual that came up — a zone that runs slow, a head that needs replacing, a wet spot that never dried. That list becomes the spring startup agenda, which is the point at which those things are cheapest to fix.

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