By Peter Spartos
Setting up your own irrigation system for your rooftop or balcony garden this spring? Fall might seem far away but it’s a good idea to understand what it will take to properly shut your system down at the end of the year. Any irrigation lines that could be subjected to freezing temperatures will need to be winterized. Typically this just means any lines that are outside of the building envelope, but if lines pass through an unheated indoor space these might need to be winterized as well.
Irrigation system winterization is a simple, but necessary process. It involves completely clearing all water from the lines that could otherwise freeze and expand, so much so that the lines could potentially crack or burst.
The first step is to shut off the water supply at a point where there is no risk of pipes freezing. If you have a frost-proof hose bib this is as simple as turning off the outdoor spigot as usual, but otherwise, the water supply will need to be shut off where there is no risk of water freezing (usually a shut-off valve located in a climate-controlled indoor room).
The next step is to evacuate water from the lines. If you have an incredibly simple and small set-up, water can be drained out passively. However, more complex systems need to be “blown out” using an air-compressor so that water completely evacuates all the irrigation lines. Even micro-tubes and emitters, which are commonly used for drip irrigation, can hold water inside and potentially freeze and crack. Another concern is that there are usually places where irrigation lines are coiled or horizontal, often hidden below the soil surface, where water can pool and end up trapped. Just one pocket of water can be enough to cause freeze damage.
Air compressors are versatile tools that can be used for all sorts of tasks. They are relatively inexpensive (for a little more than a hundred dollars you can get a capable electric model). They can also be easily rented. However, it is important to use an air compressor that allows you to monitor and control the air pressure because if pressure inside the system gets too high, it is possible to damage or crack the irrigation plumbing, which is exactly what you’re trying to prevent ice from doing. Generally, pressure at 25 psi is sufficient, though some larger systems might require more pressure.
To connect the high-pressure air compressor hose to your irrigation system you will need an adaptor. The specific model will depend on the size of your air hose tubing and irrigation hook-up.
Hook the air compressor up to your irrigation system past the point where the main water source has been shut off, then activate the irrigation system to run through a full cycle. The irrigation controller controls the opening and closing of valves, so when the irrigation cycle is on, valves open and allow the compressed air to pass through instead of water. Turning on the irrigation system before the air compressor is on prevents pressure from the attached air compressor to climb to a dangerous level. When turned on and the irrigation valves are open, pressure will build up and eventually start displacing the water out of the hoses. When this happens you should hear a “hissing” sound as water starts to move out of the lines.
This is an important time to have your eye on the pressure gauge on your air compressor. With the water providing resistance this is where there is a risk of hitting too high a pressure. If you are able to check your emitters, where water is delivered to the plants, you should see water dripping out of these as if the system were running as usual. If your system happens to use popup irrigation heads these should pop up and start spraying water.
When water has been completely blown out of the lines, you may hear a whistle sound (much like a tea kettle), caused by air and water droplets escaping through the emitters at the same time. Drip irrigation can take quite a bit longer to evacuate. So, it is a good practice to walk each zone as they are being evacuated and visually inspect the drip lines at their terminal points to ensure water is no longer flowing from the emitters. At this point, the air compressor is unable to hold pressure in the system as there is no more water preventing air flow. To be safe and certain, let the compressor run for another couple of minutes because if water droplets are left in the lines, they could settle back down to a low point and pool, creating a possible freeze point.
Repeat the same process until you have moved through all zones within the system. After lines have been blown and the air compressor is disconnected, it is a good idea to wrap some electrical tape over the hose opening to prevent any debris or critters from getting inside. Irrigation lines, with their very small drip emitters, are more likely to get clogged by internal debris than regular hoses.
A good rule of thumb for shutting off irrigation systems is that it’s better to be a few weeks early than a few days late. Shutting off water a few weeks earlier than necessary might put plants through some drought stress, but if the system is closed too late in the season, there is a risk of freezing, which can cause major damage to the irrigation. It’s a good process to be prepared for well ahead of time, rather than saving for the last minute.
Review of steps for winterizing irrigation:
- Shut off the main water source.
- Hook up your air compressor, but do not turn it on.
- Turn on the irrigation system.
- Turn on your air compressor (you may need to open a water valve).
- Allow the water to be pushed out of the system, making sure pressure stays around 25 psi.
- Let the air compressor run for 5 minutes once air is coming out of all the emitters.
- Switch the irrigation controller to run the next zone.
- Once finished with all the zones, wrap some electrical tape over any open plumbing.