Irrigation in the Pacific Northwest

FAQs for Residential (Lawn and Garden) Irrigators

Why should residential homeowners care about irrigation management?
When do I turn my water on in the spring?
How long do I leave it on?
How much water am I putting on?
What are the environmental and health consequences of poor irrigation management?
I’m dragging hose to irrigate my lawn and garden. What are good strategies for being efficient and effective?
What kind of irrigation system should I put in? What kind of sprinkler heads? Can I design it, or should I have a professional do it?
I have an automatic irrigation system. How should I set my timer?
What features should I look for in an irrigation timer?
It’s a water short year and I don’t have enough water. What should I do?


Select another FAQ or tutorial.


Why should residential homeowners care about irrigation management?


Water costs money. Someone who does a good job of irrigation management will have a greener lawn, better landscaping, and a lower water bill than someone who doesn’t. Poor irrigation management also has an environmental impact because water is a limited resource. The more we use, the less water is available for alternate uses. Water is also the primary vehicle that moves fertilizers and pesticides off of landscapes and carries them into our streams and water bodies where they can cause environmental damage.


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When do I turn my water on in the spring?


It depends on your location, the weather, and how much precipitation (water) was stored in the soil over the winter as snow melt and rain.


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How long do I leave it on?


Leave the water on just long enough to fill the root zone up to field capacity. In order to know this you will have to have a good idea of your sprinkler application rate or drip irrigation system.

Also see How much water am I putting on? and How should I set my irrigation timer? for more information.


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How much water am I putting on?


You can calculate it for sprinklers, a line-source drip irrigation system, or for an area as a whole. Under sprinklers, you can measure the applied water by putting out straight-walled cans (soup or tuna cans) for a measured amount of time and measure how much water is caught in the can. You can then divide the catch depth (inches) by the time (minutes) to get your application rate in/min. You then multiply this rate by the time to get the application depth.


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What are the environmental and health consequences of poor irrigation management?


Water is the primary vehicle for moving fertilizers and pesticides out of the soil where they are needed and useful into groundwater, streams, and water bodies. Drinking fertilizers and pesticides that are pumped out of wells from the groundwater can have negative health effects.

Fertilizers help plants grow. In streams and water bodies, excessive fertilizers and nutrients will promote aquatic vegetation and algae to the point that they choke out other native plant species and consume so much of the water’s oxygen that fish and other aquatic animals are negatively impacted. When too much irrigation water is applied, water will either run off or move down through the soil past the bottom of the root zone where the plants can no longer reach it. When this happens, it can cause erosion and/or move nitrogen and soluble phosphorous with it.


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I’m dragging hose to irrigate my lawn and garden. What are good strategies for being efficient and effective?


It is hard to apply water uniformly dragging hose. Set a timer so that the water doesn’t stay in one area too long. Know how much water you are applying so that you can time it right and arrange for sprinkler overlap. I suggest operating your lawn just a little on the water stressed side. This helps you to visibly see where you need to water (look for darker green, stiffer or rolled grass blades, and brown spots) and helps to prevent you from over-watering and wasting water. Lawns are really just decorations anyway (unless you’re running a preschool).


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What kind of irrigation system should I put in? What kind of sprinkler heads? Can I design it, or should I have a professional do it?


I am assuming you are talking about an automated irrigation system. Pop-up sprinklers are the most popular. The sprinkler heads depend on your system’s operating pressure, flow rate, and area that you want covered. You will be slightly more efficient with sprinklers with larger drops, and those that don’t throw the water long distances.

Watering lawns and flower beds with drip irrigation is a very efficient way to irrigate, but it will cost a little bit more to set up. If you plan to put in a drip irrigation system for a lawn, it should be installed before the grass is established. Otherwise you will end up digging up the entire lawn to put it in.

As far as designing it, you may not want to do things the way that I do, which is to try to figure it out by yourself and ending up spending much more time and money on it than if you had it professionally designed in the first place. But if you are adventurous there are pamphlets and books on how to design and install your own sprinkler system (check your library). Sometimes there are trained (? big question mark here) people in hardware stores who will design your irrigation system for you if you buy your components there. It helps to remember what motivates people, and a hardware store designer may not give you the low-cost, most efficient solution.


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I have an automatic irrigation system. How should I set my timer?


Let’s start with what not to do. Don’t set it once and leave it on the same setting all summer long (e.g. 15 minutes every morning). Your lawn and garden do not need the same amount of water in the spring and fall as they do in the middle of the summer. For example, lawns in Yakima, WA use about ¼ of an inch per week in April and October, 1¼ inches per week in May and September, 1.6 inches per week in June and August, and a little over 2 inches per week in July. If you left it on a single setting, you would typically be over-irrigating in the spring and fall (wasting water) and under-irrigating in the middle of the summer. You should reset your timer at least once a month.

On a silt-loam soil, I recommend putting all of the water on in one irrigation and leaving the timer off the rest of the week. Soil can only hold so much water and we don’t want to put on more than it can hold, so during the hot summer months, split it and put on half of the total irrigation requirement in two irrigations per week. On sandy soils, you will have to irrigate more often than that. However, try not to irrigate every day. The more often the leaves and soil surface are wet, the worse your irrigation efficiency will be and the more problems you will have with plant diseases. Also since you aren’t watering very deep, your roots won’t grow very deep and will be more prone to drought stress.

The bottom line, water deeper at less frequent intervals.

Irrigation systems should be turned off when it rains. This can be done with an automatic rain shut-off sensor. This will save you money, save your utility company water, and be environmentally responsible.


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What features should I look for in an irrigation timer?


Irrigation timers are getting more sophisticated with time. In fact, the latest thing in timers is “smart controllers”. These automatically sense your lawn and garden’s changing water needs (changing with rain, weather and season) and simply turn on the water for you only when it needs to be on. They either estimate evapotranspiration (ET) or measure soil moisture directly, and then adjust the water schedule for you. Although you will pay about three times the cost of a regular controller, users are typically seeing 20 – 40% reduction in water use while maintaining grass quality.


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It’s a water short year and I don’t have enough water. What should I do?


I suggest a brownish lawn for the summer. You will do a lot less mowing, and your water bills will come down significantly. Grass that is water stressed uses a lot less water. Most grass varieties will go dormant if they totally run out of water. The grass is still alive and will green up when water is reapplied the next year, or later in the season. When you can water, do it at night (more efficient) and when the wind is calm.


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