Q. We typically have hot summers (month long +100 degree weather,) but recently we are also experiencing very cold winters (recently had 0 degree with -17 degree wind chills that froze a lot of pipes in the city.) Do you have any suggestions that would be useful about winterization for Southwest USA irrigation, or any particular materials that are specific to this area I should ask for?
A. This is a situation which occurs all through the southern US, as far inland as Nevada (Reno sees this type of temperature extremes every year), and up the west coast all the way into the Pacific Northwest. In these areas you see overnight freezing, which is typically followed by above freezing daytime temps. To make it worse, it is often necessary in these areas to irrigate during the winter months due to drying wind and high daytime temperatures! In these places we generally don’t winterize irrigation systems by draining the pipes in the winter, as the soil insulates them enough to prevent freezing. Sometimes we bury pipes much deeper in these places, say 18″, to keep them below the frost level. Any above ground equipment will need insulation installed on it to prevent freezing during the nights. So generally I wrap the above ground pipes with foam or fiberglass insulation, extending down underground to below the typical freezing depth. Where exposed to sunlight I wrap the insulation with a high grade pipe wrap tape that is UV resistant, or with metallic tape. Without protection foam insulation degrades pretty fast from sunlight exposure. Do not use standard duct tape, it is not UV resistant and will be a mess within a year or two. For above ground valves and backflow preventers you can purchase insulating covers that can be placed over them like a big bag, (one brand name that comes to mind is Polar Parka) or you can wrap them in fiberglass pipe insulation wrap. Just make sure water can drain out of the bottom someplace, in case there is a leak. Fiberglass insulation must be wrapped with plastic tape or something else waterproof to keep it dry, it will not insulate if it becomes wet. You can also put thermostat controlled electric pipe heaters on the pipes as another option.
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The killer problem is when you have hard freezes that last for several days. Insulation doesn’t work very well during long duration freezes, as the cold has time to penetrate the insulation. In areas where freezing weather lasts longer than over-night, but you still need to keep the irrigation system operational, it is a good idea to install electric pipe heaters on backflow preventers and above-ground valves. If you don’t need to irrigate during the winter in hard freeze areas, then you should do a full winterization process that includes draining water from the pipes. For more details on winterization see the Irrigation System Winterization Tutorial.