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 > > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://www.pacificbulbsociety.org/list.php