09.30.14Alan Harris

Fall Back for Water Conservation

Fall TreeAutumn is the time to fall back on irrigation run times to minimize water use.

Fall is in the air and the trees are beginning to show their fall colors. We know when the time comes to change our clocks we will “Fall back an hour”. Now is also the time to “Fall back” on the irrigation run times to minimize water use in the landscape.

Fall Means Shorter Days

Shorter days means less sun and less time for plants to grow. Less plant growth means most plants need less water.

The exception to the less growth rule are plants which prefer cooler temperatures. One example is annual rye grass which is used in some markets to overseed dormant warm season grass to provide a green lawn in the winter. Annual rye grass prefers the cooler temperatures and uses an incredible amount of water for germination and establishment.

Fall Means Cooler Temperatures

In almost every part of the country the temperatures are starting to fall. Even in warmer climates the temperatures are less than they were a month ago. Lower night temperatures mean the soil temperature stays cooler for a longer time in the morning which reduces evaporation.

Fall Means Lower ET Rates

Shorter days and cooler temperatures means lower Evapotranspiration (ET). The term comes from the words evaporation (water loss from the soil) and transpiration (how much the plant transpires or sweats). For example in North Atlanta the ET rate has decreased in the past 30 days from 0.22 inches to 0.05 inches per day. To find local ET rates for your area check with your local water authority, county extension service or local university. Here is another example from Denver Water. 

Using ET to Calculate Corresponding Run Time

Good news…if you have a smart irrigation controller the calculations are performed automatically. However, if you have a dumb irrigation controller you will have to change the program yourself. If you happen to have an advance degree in math and love to solve problems such as PR (in/hr) = 96.3 x gpm/Area (ft2) and terms like Water Budget, Adjusted Run Time and Base Schedule Index don’t scare you then read the technical paper Irrigation Scheduling – Use “ET” to Save Water by Rain Bird.

ET Calculators

If advance math is not your expertise, but you still have an irrigation controller you need to manually change the program, here are a few calculators to help make your life easier.

If you don’t have a smart irrigation controller, but have a smart phone Ewing Irrigation has an app to help you determine how long to run each irrigation zone to replace the water lost to ET.

The “Water My Yard” program is a web based tool for Texans to minimize their water use. It only takes three short steps to begin and then you will receive a weekly email letting you know how much water your landscape requires based on local Texas weather conditions.

For people in Florida and Georgia there is an app to determine how much water is needed to grow healthy grass. Grass usually is the largest component of the landscape in the southeast and one where overwatering is common.

If you don’t live in Texas, Florida or Georgia you can use Gnome by ETWater. This web based ET calculator takes into consideration plant type, type of irrigation head, soil, slope and solar exposure to determine the amount of water the landscape requires each week. Gnome will even suggest start times and watering days for your irrigation controller.

Let’s Be Honest

Most people won’t take the time to manually change the run times on their irrigation controller every week. Your best alternative is to upgrade to an EPA WaterSense labeled smart irrigation controller.

What if you could make your dumb irrigation controller smarter for less than $70.00 and only had to turn a dial to save water? The WaterDex is just such an add-on device for a dumb irrigation controller. The remote dial is wireless so it can be mounted in a location convenient to you such as on the refrigerator in your kitchen. Based on your zip code WaterDex will email you the % to adjust the run time. The setting for North Atlanta with the lower ET rate is 61% for this week.

Inspect What You Expect

Any time irrigation is adjusted up or down keep a watchful eye on the landscape. If plants are wilted in the morning more irrigation may be needed. If water starts to run off it means the soil is saturated and water is being wasted. Here are a few other tips to save water in the landscape.

If we missed your favorite ET calculator or add on ET irrigation device please leave a comment in the section below.

For more water and irrigation information follow me on Twitter @h2oMatters and check out water stories I am reading on Flipboard:


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Alan Harris

Alan Harris is a water management pioneer. With roots in landscape architecture, Alan has worked with irrigation throughout his career experimenting with hydrozones and a variety of high efficiency irrigation systems. Now, over thirty years in the landscape industry, Alan continues to stay apprised of the latest technology even in a sales leadership capacity as our Director of Sales Operations for our landscape maintenance division. In addition to his contributions to this blog, Alan keeps his hand in water management as a regular contributor to Lawn & Landscape Magazine and speaker at WaterSmart Innovations Conference.


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  1. Wednesday, 8:34 Alan Harris

    Glad to see this post inspired others to write and expand on the topic. Read what Mike Mason from Westhermatic has to say on the topic of ET and smart controllers:

  2. […] smart controller was hung on the wall with care, in hopes the ET information would soon be […]

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