Winterize a sprinkler system before the first hard freeze. Water left in the pipes turns to ice and expands. Ice cracks pipes, splits valves, and breaks the backflow preventer. A repair that costs little in November can turn into a dug-up yard in April.
This guide covers when to do it, the three ways to clear water from the lines, the steps in order, and when to hire a contractor.
When to winterize in BC
Do it before nights fall below freezing for several days in a row. That date depends on where you live.
In the Interior, Kootenays, Cariboo, and Northern BC, hard frost often arrives in October. If you are reading this in November in those regions, do it now. On the south coast, including Metro Vancouver, the Fraser Valley, and Vancouver Island, freezes come later and are shorter. Many systems there still have a few weeks. A single cold snap can still freeze an exposed pipe or backflow device.
Elevation changes the date. A yard on a hill freezes sooner than one in a sheltered valley. Check your local forecast and watch the overnight lows.
Three ways to clear the water
Manual drain. Some systems have drain valves at the low points of each zone. You open them and the water runs out by gravity. This is the simplest method. It only works if the pipes slope to those valves.
Automatic drain. Some systems have valves that open on their own when the water pressure drops. Water drains from the lines after you shut off the supply. Check that each valve opens and is not blocked by dirt or roots.
Blow-out. An air compressor pushes the water out through the sprinkler heads. This is the most common method for BC systems because it clears the water that gravity leaves behind. It is also the method that can do damage if done wrong. Read the section on air pressure below.
If you do not know which type you have, look for the original installation plans or ask the contractor who installed it. A system with no drain valves needs a blow-out.
Step by step
1. Turn off the controller. Set the timer to the off or rain mode. Do not unplug it unless the manual says so. Many controllers lose their schedule when they lose power.
2. Shut off the water supply to the system. Find the irrigation shutoff valve. It is often in the basement, a crawl space, or a utility box near the water meter. Close it fully. Do not touch the main house shutoff.
3. Relieve the pressure. Open the test cocks or bleed valves on the backflow preventer. Then run a zone briefly to let the last water out of the line.
4. Drain or blow out each zone. For a manual drain, open each drain valve and leave it open until the water stops. For a blow-out, connect the compressor to the blow-out port, then work through the zones one at a time. Start with the zone farthest from the compressor. Run each zone until only mist comes out of the heads. Then move on. Short bursts are better than long ones. Air with no water in the line can heat and damage sprinkler heads.
5. Drain the backflow preventer. This device sits above ground on many homes and is the part most exposed to cold. Drain it. Leave the handles on the shutoff valves at a 45 degree angle, halfway between open and closed, so any water left inside has room to expand. Wrap the device in an insulated cover or bring it indoors if the manufacturer allows.
6. Drain the drip lines. Drip irrigation tubing holds less water, but it can still split. Open the end caps and let it drain. Use low air pressure if you blow it out.
7. Leave the controller and valves ready. Leave the valve boxes closed and dry. Pull the controller’s rain sensor battery only if the manual says to.
Air pressure and safety
Too much air pressure bursts pipes and fittings. Check the pressure rating of your pipe, valves, and heads. Use the lowest pressure that clears the water. Polyethylene pipe and drip lines tolerate less pressure than rigid PVC. If you cannot find the rating, call the installer or a contractor.
Wear safety glasses. Never stand over a sprinkler head or valve when air is moving through it. Do not connect a compressor to the system without a regulator and a gauge.
A small household compressor may not move enough air volume to clear a full system. Check the compressor’s air flow rating against what the system needs. This is a common reason homeowners hire out the job.
Do not forget the hose bibs and rain barrels
Disconnect garden hoses from outdoor taps and drain them. A hose left attached traps water in the tap and can freeze the pipe behind the wall. Close the indoor shutoff to the outdoor tap if your home has one, then open the outdoor tap to drain it. Frost-free taps still freeze if a hose stays on.
Empty rain barrels or lower the water below the spigot. Leave the spigot open.
Check local rules for backflow devices
Many BC municipalities require backflow preventers on irrigation systems. Some require a certified tester to inspect them on a schedule. Rules differ by city and regional district. Check with your local government before you drain or remove the device. Ask whether testing is due in spring.
When to hire a contractor
Hire an irrigation contractor if the system has no drain valves, if you do not know the pipe rating, if you do not own a compressor with enough air flow, or if the backflow device needs a certified test. Many irrigation companies book blow-outs in fall, so call early.
Irrigation is a specialty trade. A general landscaper may subcontract it or may not offer it. The guide on who to hire in BC explains how landscapers, gardeners, arborists, and lawn care companies differ.
Before you book anyone, ask for proof of licence, WorkSafeBC coverage, and liability insurance. Ask what the price includes, such as the number of zones and the backflow device. Ask who pays if a pipe breaks during the blow-out. The full list of checks is in how to hire a landscaper in British Columbia.
Pair it with fall cleanup
Winterize the system when the beds are clear. Leaves and debris can hide valve boxes and heads. The fall yard cleanup checklist lists the work to finish first.
Mark the sprinkler heads with flags before snow comes. Plows, shovels, and snow blowers break heads that people forget are there.
Landscaper List is a new directory with no listings yet. These steps apply to any irrigation contractor or landscaper you find through a neighbor, a nursery, or a local search.
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