The recent asphalt-melting, crop-withering, and blackout-inducing heat waves are one of the practical demonstrations we’ve seen lately of how the weather is getting more extreme and less predictable.

The same applies to snappier cold snaps, sometimes even pre- or post-winter.

So if you don’t blow out and winterize your sprinkler system, even in areas where it didn’t use to be necessary, you’re risking a steep repair bill plus a hacked-up lawn come spring.

Why Winterize Your Sprinkler System (What’s the Worst that Could Happen?)

Unlike almost all other liquids, water expands as it freezes. Therefore, a pipe that’s completely filled at 32 °F (0 °C) needs to get about 10% larger as its contents turn to ice – or else.

This process is as inevitable as the sunset – even tough materials like brass (used in many irrigation fittings such as valves) crack under its pressure. PVC, the material that those white, rigid pipes are made of, simply shatter. Polyethylene fares somewhat better but is still more likely than not to give way.

Often, you’ll only discover the problem once everything thaws:

• If the leak is above ground and your sprinkler system was still pressurized, you may come home to an impressive puddle and/or some angry neighbors.
• Below ground, if your pipes are above the frost line, the soil may staunch the leak somewhat, but your water usage will shoot through the roof. You may or may not notice patches of waterlogged soil.
• Individual components such as sprinkler heads may be damaged, causing them to either leak or not operate when they’re supposed to.

Finding the exact location of an underground leak can be hard, even for professionals. Considering that the average sprinkler system costs over $2,000, you’d probably prefer to avoid breaking it by forgetting about winterization.

How to Winterize Your Sprinkler System

Now that we’ve covered the “why”, let’s get to the “how”.

One approach could be to add non-toxic antifreeze to the water, as is sometimes done when winterizing an above-ground swimming pool in mild climates. As it turns out, this isn’t sufficient.

You’ll have to remove all or nearly all of the water in your pipes.

First Steps

It wouldn’t make a ton of sense to empty your irrigation pipes if they’re just going to be filled again, so make sure you close the main shut-off valve to your sprinkler system firmly. This valve may be located near your water meter, close to your sprinkler controller, or in your basement where the irrigation mainline splits off from your household supply. Trace the pipes you can see (and guess at the location of those you can’t) until you find it.

Almost certainly, at least a short length of pipe and perhaps the shut-off valve will be located above ground and outside. The best you can do for them is to add insulation; warmth from the upstream side should then keep them from freezing solid.

Finally, you’ll need to put your automatic sprinkler controller to sleep for the winter.

How you go about this depends on what kind of unit you own. With a controller that’s difficult to program but contains an electrical connection for a rain sensor, it’s easiest to short out the rain sensor contacts. This tells the controller that the ground is wet enough not to need irrigation, but doesn’t erase your time and zone settings like unplugging it would.

More advanced models have a special “hibernate” mode you can select from your phone. In either case, if your controller has a relay contact hooked up to a pump, make sure to disconnect these wires. Running a pump dry or against a closed valve is sure to burn it out.

Clearing the Pipes

This, the most important part of winterizing your sprinkler system, can take quite a while. You probably have more entertaining things to do on a Saturday morning in fall, but trust us: it’s essential to get those pipes dry.

The best way of draining your irrigation network depends on how your how your sprinkler system is designed. If you don’t know, you can try to contact the previous homeowner or original installer. Should you be unable to figure it out, you should either use the blow-out method (carefully) or call in a professional to do the job each winter.

Automatic Draining

Some sprinkler systems contain special components that allow water to siphon away whenever the water pressure drops to something under 10 PSI. If you have one of these, simply:

• Run one of your sprinklers – it will squirt a little at first. Keep it on until it stops sucking in air.
• Pull up each sprinkler head to release any water stuck inside.
• Open the small drain valves (if present) on your backflow preventor, filter, etc.

Manual Draining

If the lowest points of a sprinkler system are accessible, these are commonly fitted with drain valves. Simply open all of them (and remember to close them again when the water stops running).

Just like with automatically draining systems, you then have to manually activate each sprinkler head to release moisture trapped around the solenoid and drain the upstream portion of the system.

How to Blow Out a Sprinkler System

The third method of winterizing irrigation pipes involves hooking up an air compressor to your mainline and forcing all the water out.

There are two potential problems with this approach, though:

• Most DIY air compressors can generate the required pressure but fall short on CFM (flow rate). They’ll therefore struggle to get all the water out of any but a very small network of pipes.
• Some sprinkler systems are not designed to be blown out and may get damaged.

If you can use the blow-out method, there will be a connection point for air near your sprinkler controller but after the backflow device. Close the main shutoff valve, slowly open the valve on the compressor, and activate each sprinkler zone one at a time until no more water comes out.

You can either start with the most elevated zone and work your way down, or at the zone furthest from the compressor and work your way inward.