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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Oct 07

Shorter Fall Days Mean Less Thirsty Plants

Posted on October 7, 2015 at 11:29 AM by Ann Vallee

by Dan Carney, Water Conservation Manager

Believe it or not, this is the time of year when people tend to overwater the most. Many customers (we’re not naming names) keep their irrigation systems running at peak summer levels until well into fall. It’s understandable: On warm, sunny autumn days, it’s easy to assume our plants are pretty thirsty. But are they?

 evapotranspiration
 Evapotranspiration
Your plants’ water needs depend on the rate of evapotranspiration—that is, how much water is being lost into the air via evaporation from soil and transpiration from plants (see diagram). Between August and November, as the days grow shorter, the evapotranspiration rate drops about 40%. On top of that, many plants are entering their dormant phase. This means that—rain or no rain—your garden just doesn’t need as much water this time of year.

The bottom line: Turn down the run time on your irrigation system in the fall and prepare to turn it off for the winter if we get normal rainfall. If you’re not sure how much water your garden needs, use our Weekly Watering Schedule as a guide. Finally, be sure to visit our new water-wise gardening website for examples of beautiful gardens that provide year-round beauty, are friendly to the environment, and need less water all year!

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