pbs Digest, hardiness, cold temperatures

ConroeJoe@aol.com ConroeJoe@aol.com
Tue, 28 Dec 2004 15:11:59 PST
John Bryan <johnbryan@worldnet.att.net>

> Obviously plants that are borderline will succumb to a hard frost. But I
> am still of the opinion that going into cold weather dry will give the
> plants a better chance to survive. Thicker antifreeze as it were.


It was interesting to see the leaves of my Nerine collapse due to cold (ca. 
23 F).  They have straightened out and are upright again and there is no 
apparent damage.  

I interpret the collapsing as due to a mechanism the is an emergency response 
to cold.  The loss of moisture in the leaves would indeed increase osmolality 
and would also cause the leaves to collapse.  The increase in solute 
concentration could easily protect plants from cold damage, but I cannot be sure this 
is what happened without further experimentation.

Many cacti from cold winter  areas (e.g., Rocky Mountain states) shrivel up 
in preparation for winter--they can loose so much water that some columnar 
types (6-8 inches tall plants) can appear to shrink into the soil.  Also, several 
species of Opuntia loose so much water in winter that their pads look like big 
green prunes.  The link below shows O. humifusa all ready for winter, the 
plants actually shrivel and collapse onto the soil surface.  

However, other Opuntia survive zone 6-7 temperatures without shriveling.   I 
don't know if they loose moisture or not, but they don't appear to.  Such 
plants as O. dulcis or O. phaecantha can take zero F (-20 C) in stride.  

Many woody plants are known to prepare for winter by reducing the water 
content of their cells; another way to say this is that they increase the 
concentration of solutes in their cells.   See the link below, it discusses dehydration 
as a mechanism to survive very cold weather.  

I have not found scientific documentation of "intentional" water loss as a 
mechanism to protect bulbous plants from cold--but other plants use such a 
mechanism, and I think that is what my Nerine bulbs did.  

LINK:  O. humifusa ready for winter

LINK:  Woody plants and cold weather

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