John Bryan johnbryan@worldnet.att.net
Tue, 28 Dec 2004 13:50:08 PST
Dear Jim:

thanks for your message, most interesting. All the best to you and yours
in 2005. Cheers, John e. Bryan

"J.E. Shields" wrote:
> Dear Ken, John, and all,
> Ken is generally right, we don't know what makes some plants hardy to cold
> weather and others tender.  At least in many cases.  It isn't true in all
> cases.
> The physiology of a bulb or any plant changes when it switches from active
> growth to a resting phase.  Bulbs that have to survive cold weather are
> thought to convert much of their stored starch to sugars (glucose,
> fructose, sucrose) with the onset of cooler temperatures or shorter
> days.  Starch is insoluble and does not act as an anti-freeze.  Soluble
> sugars like glucose, fructose, sucrose, and perhaps glycerol are effective
> anti-freeze agents.  It makes good sense.  Plants that can prepare for
> winter in an orderly way, can survive the cold.  Plants caught unprepared
> by unseasonable freezes are often killed.
> Tender plants can not always prepare for cold weather, even when the
> progression to winter weather is normal, as we all know.  The fascinating
> ones are those that "ought" not be able to survive (so far as we know) but
> that then do, at least in some microclimates.
> There are reports describing some of the changes that have been found in
> some types of bulbs when they prepare for cold weather.  See  "The
> Physiology of Flower Bulbs," by August De Hertogh and Marcel Le Nard,
> Elsevier Science Publishers, Amsterdam (1993), for instance.
> When plants go back into active growth, the sugars are either used up or
> reconverted to starch.  A perfectly hardy plant like a dormant daylily can
> be killed when in active growth by a couple days of sub-freezing
> temperatures.  One winter, I had numerous trays of young daylily seedlings
> growing in the greenhouse in January.  We had a power outage, the
> temperatures went well below freezing inside the greenhouse for several
> hours, and every single daylily seedling died.
> Plant hormones that lead a plant to dormancy or to prepare itself to
> survive freezing temperatures include abscisic acid and ethylene.  Plant
> hormones that waken plants from dormancy to active growth include the
> gibberellins and auxins.  Abscisic acid and gibberellins are natural
> antagonists in regulating the physiology of plants.  Abscisic acid prepares
> the plant for stress; gibberellins prepare the plant to grow.
> Regards,
> Jim Shields
> in central Indiana, where any sensible plants are far below ground and fast
> asleep right now.
> *************************************************
> Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
> P.O. Box 92              WWW:    http://www.shieldsgardens.com/
> Westfield, Indiana 46074, USA
> Tel. ++1-317-867-3344     or      toll-free 1-866-449-3344 in USA
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