10 Steps to Winterizing Your Underground Sprinkler System

Late fall is the time of year to prepare your lawn and sprinkler or irrigation system for the coming winter months. To avoid the damaging effects of frozen pipes and sprinkler heads, you can either prepare your sprinkler system yourself or hire a professional to winterize your system for you.

The extent that your system requires winterizing depends on what part of the country you live in. In warm areas, it may mean adjusting the timer or turning it to the off position. In cooler parts of the country, you may need to insulate your valves and anything above ground. In very cold climates, you need to do more. If you live in a climate that freezes, you need to turn off and drain your system or turn off and blow air through the valves and pipes.

Before you start to work on your sprinkler system, however, there are a few lawn maintenance issues to address. Because leaves smother your grass, rake up excess leaves. Late in the fall is a good time to fertilize your lawn, usually about a month before it typically freezes. Your lawn has been growing all summer and the dirt may be lacking nutrients it needs to green up when spring rolls around.

Finally, in most climates you will want to cut your grass short for the winter to give plenty of room for new grass growth in the spring. In lower, warmer elevations, go ahead and leave your grass longer as this will better keep moisture over the winter. Next, it is time to discuss your irrigation or sprinkler system.

The following 10 steps address systems in a cold zone prone to freezing:

  1. Locate the main water source to the irrigation system.
  2. Turn the water supply off to your sprinkler system before the first frost by locating the shut-off valve that controls water flowing to your system. This valve is generally in an underground box below the frost line or in a heated area. In Salt Lake City, for example, the frost line is 32″ so the valve would be below that level. A special tool, called a stop and waste key or curb key, is required. The keys are available at your local hardware store. Most valves are closed by turning the valve one-quarter of a turn to the right.
  3. Open all drains, including you backflow preventer assembly, and leave them open for a few hours to allow all water to escape.
  4. Remove your sprinkler heads so the water will drain from them and not freeze during the winter.
  5. Clean out any remaining water with an air compressor, charging it to 60 pounds per square inch (psi). Start by inserting the air hose into the nozzle of the drain valve located nearest the main water shut off and force out excess water with a short blast of air. Begin next with the zone furthest from the control. Activate one zone of your system at a time and leave it open as you rotate around blasting each with air, and closing it off before moving to a different zone.
  6. Replace all the sprinkler heads and close the backflow preventer valve. One note of caution here: metal pipes can tolerate up to 80 psi but flexible hosing requires much less pressure. Higher psi’s can actually damage flexible hosing. You will also want to avoid blowing the air through the back flow as hot air can damage it. Your irrigation maintenance expert will know how much air pressure is right for your system.
  7. In excessively cold climates, you may want to add a blanket of fiberglass, or at least an old blanket or towels covered by plastic over the valves and piping in you sprinkler control box.
  8. Turn off the power to timers and remove batteries after you have blown out the water from each zone and unplug power cords or turn off the power source through your breaker panel.
  9. Cover and apply foam insulation to above ground pipes.
  10. Now is also a good time to store your lawn mower and other gardening tools for the winter.

Sprinkler or irrigation systems in warmer climates that rarely or never freeze do not need this level of maintenance. Many systems have a “rain” or “off” mode that essentially shuts off water to the valves and retains all the programming information. If you are prone to freezing even once or twice, you need to drain your main valve and you may want to cover your water supply system located underground to prevent any remaining water from expanding and breaking pipes. In warm climates, you can also shut down power to the controller but this means you will need to reprogram you system early next spring. It is also a good idea to cover and insulate above ground pipes.

The best advice you can get on what your particular sprinkler or irrigation system needs is from your sprinkler maintenance professional. Once your system is prepared for the winter, you can relax and settle in for winter!