Dew care and attention

In column 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.

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?

I don’t think that is entirely correct. See Merriam Webster 3©

A better description is found at
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?)

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”