Irrigation is a must in our climate. Even if your garden has all native plants, they will need supplemental irrigation for at least their first two summers before they become established. In addition, native plants in residential yards can look a bit bedraggled without some supplemental irrigation in the hottest months. If you’re planning on growing any non-native plants, such as fruit trees, you will definitely need an irrigation system.
The best system for our climate is a drip irrigation system. It’s about 95% efficient which will save our water and save you money. Some other efficient options include using ollas, vertical perforated pipes (for trees), or soaker hoses, although these tend to have more issues with our hard water. One thing you will definitely want to avoid is a sprinkler system — you will waste a lot of water through evaporation and runoff.
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The advantages of a drip irrigation system are many. A properly installed system applies water directly to the roots, avoiding problems from overhead watering like leaf burn and mildew. This direct application of water also deters weed growth. It produces no runoff waste, and has little water loss from evaporation. In addition, it can be easily retrofitted to existing plants, thanks to flexible hoses and DIY kits.
- Backflow preventer: keeps the water from the irrigation system from contaminating your drinking water.
- Pressure regulator: keeps the water pressure at a level that is appropriate for the irrigation system components; usually this is between 20-40 pounds per square inch or PSI
- Filter: keeps small particles from clogging your smaller tubing and emitters. This is particularly important if your water source is a well or a rainwater tank, but it is recommended for city water as well.
- Timer: controls the length of time and frequency of your waterings. Look for one that has the option of having different watering zones for different plant needs.
- Supply piping: this may be rigid PVC or flexible polyethylene tubing (preferred for DIY). This should be buried about 4-6 inches.
- Micro-tubing: this is ¼ inch flexible small tubes that attach onto the supply tubing and reach out to the individual plants.
- Emitters: these come in anything from ¼ gallon-per-hour to 4 GPH and determine how much water a plant gets.
Start with the garden design
To have the ideal system, start with your garden design. This is key, because different plants will have different water needs, and you will want to put all of the plants with similar watering needs on one watering zone. You also need to figure out how many plants you want, and their water requirements, so that you can install the appropriate size system. You don’t want a system that loses pressure before the water gets to all of your plants.
You can divide the watering areas into zones, based on the number of plants and their water needs. One way plants differ in their watering needs is size: a tree will need more water than a bush, or a smaller perennial plant. Pots will need a different watering regime, as will vegetable beds. Another difference is in the type of plant. Native and desert-adapted plants like mesquite or desert willow trees will use less water than citrus and other fruit trees, for example. It doesn’t mean that you can’t interplant these together; just keep in mind that your irrigation system will need to reflect these differences.
You can figure out how much your plants need by looking at some charts available for the Tucson climate, including Brad Lancaster’s plant lists with water requirements, seasonal watering guidelines from the City of Tucson, or the very thorough drip irrigation guide from Arizona Municipal Water Users Association. There are other helpful documents available, which are listed at the end of this article.
Another thing to keep in mind when planning your system is that you will need to be able to move irrigation out to a tree’s dripline as it grows. Many people leave the irrigation in place for years after their plants have grown to many times their original size — this is a great way to stress your plants and to waste water! Always plan for the final size of the tree, shrub, or other plant, and make sure you can move the emitters outward away from the main trunk or root ball as the plant grows. You can do this by either replacing the micro-tubing as the plant grows, or by cutting a longer piece to start with and then moving it outwards. Most irrigation kits provide plastic stakes which allow you to pin down the emitter end of the tubing where you want it to drip.
It’s also important to figure out where your water will come from. Is it city water? Well water? Or will you harvest rainwater or grey water? Perhaps you will include air conditioning condensate or discarded water from a reverse osmosis filter? Each of these water sources may need different configurations. For example, city water is provided at a pressure much higher than drip irrigation systems are designed for, so you will need a pressure regulator valve to reduce the water pressure to appropriate levels. On the other hand, a rainwater tank or grey water pipe may not have much pressure at all, and you will need to compensate for this so that your system delivers water to all of your plants. If pressure is too high or too low it will not work properly and will damage your tubing. If using rainwater or grey water, make sure you check the pressure of the water with a pressure meter to make sure it's appropriate for your irrigation system.
If you’re doing the installation yourself, make sure you use fittings and parts from the same manufacturer to ensure a proper fit without leaks. In addition, make sure you have a filter in place, since even city water can contain some particulates (mainly from older pipes) that can clog your drip emitters. The type of filter you choose may vary depending on the water source.
Once you’ve installed your system and have your plants, cover the irrigated areas with organic mulch to reduce evaporative water loss. Use rock mulch for cacti, succulents, or palms. Make sure the mulch covers all of your tubing to protect it from the sun. Inspect your system thoroughly at least twice a year. I like to walk around my yard once every week or two to make sure all of my plants are doing well; any stressed-looking plant warrants a check of the irrigation system.
More Irrigation Resources
- Drip Irrigation: The basics.
- Irrigation requirements of southwestern landscape trees.
- Irrigating citrus trees.
- General resources on watering from the City of Tucson.
- For a deep dive into the nitty gritty of sprinkler system design, here’s the drip irrigation guide from AMWUA.
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