On 3/28/2009 6:37 PM, Billy wrote:
In article ,
"David E. Ross" wrote:

On 3/28/2009 12:33 PM, Denis Mitchel wrote:
Does the temperature have to be at or below freezing for frost to form on
plants?

Thanks


We often get frost on roofs when the overnight air temperature stays
above 32F. I think this is a case of the roofing materials radiating
enough heat into a clear, cloudless sky that they might actually be
colder than the air.

For plants, however, I don't think they can lose enough heat to drop
their temperatures below that of the surrounding air. Thus, frost might
form on plants until the air temperature is actually at or below
freezing (32F, 0C).

Huh?

Live foliage does not radiate heat into a cloudless sky as readily as do
metals and minerals.

By the way, because of dissolved substances (e.g., sugars) in the
moisture that is internal to plant tissues, that moisture has a lower
freezing point than 32F.

--

David E. Ross
http://www.rossde.com/.

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