ET phone home

220px-ET_Communicator_Cropped– Do you recognize this conglomeration of parts?  In the movie a coffee can, some tin foil and wire are transformed into a “functional” phone.  If such a notion piques your curiosity, feel free to read on…

How Much Water Does Your Lawn Need?

This version of ET is EvapoTranspiration (the sum of evaporation from the land surface plus transpiration from plants. Credit: Salinity Management Guide)

It is the way that science figures out the answer to the question above.  We all know that plants need water to survive.  They take it up through their roots- then what?  Eventually, it is released as water vapor through pores on the underside of the leaves.  So, the amount of water that plants lose is exactly how much they need to replace in order to stay healthy.

Factors affecting ET:

Temperature: Transpiration rates go up as the temperature goes up, especially during the growing season.
Relative humidity: As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.
Wind and air movement: Increased movement of the air around a plant will result in a higher transpiration rate.
Soil-moisture availability: When moisture is lacking, plants can begin to senesce (premature ageing, which can result in leaf loss) and transpire less water.
Type of plant: Plants transpire water at different rates. Some plants which grow in arid regions, such as cacti and succulents, conserve precious water by transpiring less water than other plants.

It is estimated that about 10 percent of the moisture found in the atmosphere is released by plants through transpiration.  Plant transpiration is an invisible process—since the water is evaporating from the leaf surfaces, you don’t just go out and see the leaves “breathing”. During a growing season, a leaf will transpire many times more water than its own weight. A large oak tree can transpire 40,000 gallons (151,000 liters) per year.  (USGS- The Water Cycle)

When to water

 UW Banner

United Water has a seasonal lawn watering program which can help maintain healthy yards without wasting water.  All you have to do is check the daily ET number  from May to September, when the program is in effect! Then you will know exactly the amount of water that your lawn needs on that day.  You may be surprised how infrequently we really need to water!     


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