# how do plants know it's morning?

**URL:** <https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320>\
**Category:** Factual Questions\
**Created:** [July 18, 2003, 4:23am UTC](https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320 "2003-07-18T04:23:31Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![ardoriel](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@ardoriel](https://boards.straightdope.com/u/ardoriel)\
**Post date:** [July 18, 2003, 4:23am UTC](https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320/1 "2003-07-18T04:23:31Z")

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I recently read a gardening tip (I’m in no way a gardener) that says that plants drink in the morning, so you should water plants early to avoid evaporation. How do plants know it’s morning? Do they still know it’s morning even if they’re not in the sun? That’s just sort of creepy to me…:dubious:

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**Author:** ![Ruby](https://avatars.discourse-cdn.com/v4/letter/r/13edae/32.png) [@Ruby](https://boards.straightdope.com/u/Ruby)\
**Post date:** [July 18, 2003, 4:31am UTC](https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320/2 "2003-07-18T04:31:42Z")

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I understood that the reason to water in the morning was that it was the most efficient use of the water.

If you water at night, the water stays in contact with the plant longer and may cause deterioration of the roots and foliage.

If you water in the middle of the day, the water evaporates before the plant has a chance to use it.

If you water in the morning, the plants can use what they need and the balance is evaporated away so your plants remain happy plants.

Not creepy at all…unless you have a plant named Audrey II…:eek:

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**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\
**Post date:** [July 18, 2003, 4:32am UTC](https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320/3 "2003-07-18T04:32:01Z")

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Plants are photosensitive. They respond to light, via light’s effect on chemicals within the plant’s cells. Green plants also make usable energy-storing compounds in the presence of light, due to light’s effect on a chemical called chlorophyl.

Your eyes respond to light, and you know if it’s morning even if you’re not in the sun. Plants don’t “know” what time it is, but if the light is there, they react to it, just as your eyes do.

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**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\
**Post date:** [July 18, 2003, 7:27am UTC](https://boards.straightdope.com/t/how-do-plants-know-its-morning/189320/4 "2003-07-18T07:27:27Z")

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Ruby nailed it.