Tag Archives: Chilling & Freezing in Plants

Chilling, Freezing & Surviving: Understanding Hardiness & Preparing Your Plants for Winter

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Parrotia persica, Persian Ironwood, has long been among my favorite trees, for its leaf shape, substance, fall color, the overall plant form and for its exfoliating puzzled bark. Hardy to zn4 this plant is tough as nails here requiring no protective effort at all.

[A note to the reader. This is not a scholarly treatment of all of the peer reviewed material on this topic.  There are no footnotes or listed sources.  This is a product of my more than 35 years of horticultural field experience and gardening along with what I’ve gleaned from reading several technical peer reviewed articles on the subject.  Such material is difficult to read and can be off putting and intimidating to even the educated layperson.  This posting is my attempt at interpreting the research and reviews that I read in a way I think is understandable without overwhelming the reader with bi0-chemistry and the technical esoterica scientists must consider in their pursuit of understanding.  Any faults are mine.]

I’ve been thinking about plants and their response to cold having watched the deciduous trees drop their leaves, dug tender plants out of the garden and moved pots around to where they would be adequately protected from freezing temperatures.  We all know what happens to water when it freezes, going from a liquid state to a solid one, its molecules forming crystalline structures, expanded and rigid, responsible for burst water pipes and snowflakes.  Water possesses some amazing qualities, as a solid, kind of counter-intuitively, it becomes less dense floating rather than sinking even taking on some insulative qualities and stopping the convective flow of heat that is normal in liquid water.  At the instant of freezing water releases a small but measurable amount of heat. What happens inside plants when temperatures drop below freezing? How does the plant keep from bursting its own cell walls like the water in pipes within an unheated crawl space or wall cavity of a building?  You’ve seen what happens to plants like Coleus and the sodden black heaps they become upon thawing out. Continue reading

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