# Dew care and attention **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [April 22, 2002, 2:22am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905 "2002-04-22T02:22:02Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [April 22, 2002, 2:22am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905/1 "2002-04-22T02:22:02Z")
In column [http://www.straightdope.com/columns/020419.html](http://www.straightdope.com/columns/020419.html) Cecil failed to mention the most obvious plant excretion process. Dew on grass in the morning is the liquid excretion of the grass during the night. Grass runs a powerful pumping mechanism to bring moisture from its roots to its leaves where it is used in respiration and photosynthesis. At night the pumping mechanism keeps on going but there are no processes to use the water - as in daytime - or to evaporate it. The grass can’t use it so it excretes it. The result is dew. There are those who will no doubt bring up condensation as seen on a cold tin roof, but that is a minor effect compared to the excess liquid pumped out by the grass. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [April 22, 2002, 4:29am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905/2 "2002-04-22T04:29:16Z")
The phenomenon you describe is called _guttation_ which could be considered a form of excretion. But it is not the same as dew. Dew, by definition, is formed by the condensation of atmospheric water vapor, while guttation is formed by exuded sap. I suspect condensation is the more important phenomenon in making the grass wet most mornings. Do you have a citation showing that guttation is more important? ---
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [April 22, 2002, 4:43am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905/3 "2002-04-22T04:43:44Z")
> [@](#): > > _Originally posted by bibliophage \* > \*\* Dew, by definition, is formed by the condensation of atmospheric water vapor_\* I don’t think that is entirely correct. See Merriam Webster 3© > [@](#): > > Main Entry: dew > Pronunciation: 'dü also 'dyü > Function: noun > Etymology: Middle English, from Old English dEaw; akin to Old High German tou dew, Greek thein to run > Date: before 12th century > 1 : moisture condensed upon the surfaces of cool bodies especially at night > 2 : something resembling dew in purity, freshness, or power to refresh > 3 : moisture especially when appearing in minute droplets: as a : TEARS b : SWEAT c : droplets of water produced by a plant in transpiration > > - dew transitive verb > - dew·less /-l&s/ adjective A better description is found at [http://www.newscientist.com/lastword/answers/688plants.jsp?tp=plants1](http://www.newscientist.com/lastword/answers/688plants.jsp?tp=plants1) Also, practical experience says that guttation is far more prevalent than condensation. How often does a tin roof get condensation and how often does the lawn have dew? A tin roof is pure condensation and you rarely get water on a tin roof unless it is foggy, while you often get a dew. Guttation is a close analogue to urination in that excess fluid is disposed of. The only difference is that urination is also used to dispose of unwanted chemicals where guttation is unlikely to do this (perhaps a Phd thesis for someone here?) ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [April 22, 2002, 6:11am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905/4 "2002-04-22T06:11:06Z")
Jezza, you must not live in Houston - almost any morning I can go outside to find my car is wet. I don’t park near sprinklers. It’s condensation. ---
**Author:** ![jezzaOZ](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jezzaOZ](https://boards.straightdope.com/u/jezzaOZ)\ **Post date:** [April 22, 2002, 6:18am UTC](https://boards.straightdope.com/t/dew-care-and-attention/104905/5 "2002-04-22T06:18:04Z")
> [@](#): > > \*Originally posted by Irishman \* > \*\*Jezza, you must not live in Houston - almost any morning I can go outside to find my car is wet. I don’t park near sprinklers. It’s condensation. \*\* You must live in Ireland where the weather forecast is “fine weather with only half an inch of rain clearing to sunny with occasional showers”