Is Sprinkler Winterizing Necessary?

Recently we received an inquiry asking if it really is necessary to winterize sprinklers, or as the question was worded, "Do I need to worry about winterizing my sprinkler system?" Great question. I thought I'd post my answer here for others to see.

Here is the full copy of the question:

We recently bought the house at the location noted in NW Portland. From what I can tell, the sprinkler system is 100% underground. The house was built in 1999. Based on my location and the fact the systems appears to be completely underground, do I need to worry about winterizing my sprinkler system?

The short answer

Most people want to protect their sprinkler system. They know there is a significant investment and they want to protect it. By blowing out the sprinkler system with compressed air, they gain a sense of confidence that they have protected the investment. They want to ensure that the sprinklers will work properly for years to come.

The full answer

The main thought here seems to be—if it's underground how can it freeze? The simple answer goes something like this. During periods of freezing weather, the frost level sinks deeper and deeper into the soil. How deep the frost goes depends on how cold it is and for how long. After temperatures rise above freezing, the soil gradually thaws out.

But how deep does the frost line really go? Again the simple answer—generally just a few inches in the Portland metro area but there's more to the story. In particular the variables really matter! But consider what the City of Portland, Oregon requires. The water service line to the house must be 24 inches deep. They want it eeper than those typical several inches deep frost line, a lot deeper.

Ok, so how deep is your sprinkler sytem buried? Most sprinkler system lateral lines are at a depth of 8-12 inches; valves are around 12 inches; and the double check anti-siphon device at between 12 inches and 24 inches.

Now let's look at the variables

  • You really don't know what's under the ground and you don't know how deep it is!
  • Sometimes it gets really cold and it lasts a long time. When this happens the frost line goes deeper.
  • Micro climates matter.
    • If there is a very windy spot the cold goes deeper in that area.
    • Maybe there is a concrete retaining wall with sprinkler pipes just on the other side. The cold comes from the top and from the side, so it penetrates a lot more.
  • Even soil conditions, mulch or the lack thereof, vegetation, and other things influence how deep the frost penetrates.

What may break in a freeze and what happens then?

  • Pipes can crack if they freeze when filled with water.
  • Similarly the pipe fittings can crack.
  • Valves and anti-siphon devices can also be affected. These are the most expensive parts.

For some parts, especially those made of metal, the affects of alternately freezing and thawing are cumulative. You may get by for years and then something breaks. I've seen this particularly with galvanized pipe. It seems to hold strong for years—and then it splits.

The full care package

Winterizing your sprinklers is just one part of ongoing care for your sprinkler system. Possibly an even more helpful service is the Spring Tune Up. That service activates the sprinkler system by closing drain valves, turning the water on, and then cleaning and adjusting the sprinklers as needed. If the sprinklers are not cleaned and adjusted regularly, sprinkler system performance will deteriorate.This is also an opportune time to do any needed repairs just before the watering season begins.


Well, I hope that helps.

David Frohmader