Cold Terminology

James Waddick
Tue, 13 Nov 2007 14:06:50 PST
Dear Friends,
	it seems to me there is a lot of comparison between Apples 
and Oranges going on here.

	"Frost- the er, white frosty stuff, is a physical result of a 
combination of temperature (air and surface) as well as humidity and 
barometric pressure (altitude). It is not a specific temperature.

	Freeze - is the empirical standard temperature where water 
freezes- i.e. 32 F or 0 C.

	Cold Damage - can occur in plants depending on a wide variety 
of factors unrelated to frost or freeze. Experience from many growers 
suggest that there are a few specific temperature thresholds:

	50 F. some extremely sensitive tropical plants such as 
Sansevieria, some orchids etc show definite signs of damage at 
temperatures around here or less. Leaves can show necrotic spots and 
discoloration below 50 F.

	32 F	There obvious damage due to freezing of water crystal 
in succulent foliage. Leaves collapse and desiccate.

	25 - 27 F - a commonly low temperature for some marginally 
hardy plants. Able to be unaffected by freezing temperatures, but 
just barely.

	15 F or so for another group of slightly hardier plants.

	The observant may see some relationship with Hardiness Zones 
in 10 degree increments. I think  growers with a wide experience in 
different climates and keen observation skills will see that some 
plants can simply tolerate more or less heat/cold than others.

	Just a suggestion.		Jim W.

Dr. James W. Waddick
8871 NW Brostrom Rd.
Kansas City Missouri 64152-2711
Ph.    816-746-1949
Zone 5 Record low -23F
	Summer 100F +

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