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).

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening diary at http://www.rossde.com/garden/diary