Cold Tolerant Woody Plants Can Be Hardy in Below Freezing Temperatures

Summary: Cold tolerant woody plants can be hardy in below freezing temperatures, according to Lee Reich's Feb. 1 article in the Ottawa Citizen.

Icy glaze encases tree. Despite cold challenges, healthy plants are able to survive and thrive; Wednesday, Dec. 12, 2007, 13:14: Ed Roberts, CC BY SA 2.0 Generic, via Wikimedia Commons

Shrubs, trees and vines are cold tolerant woody plants that have a survivalist agenda, according to an article published Feb. 1, 2016, by Lee Reich, Ph.D., in the Ottawa Citizen, Ontario, Canada.

Cold hardiness belongs high on the list of woody plant attributes when what a shrub, tree or vine needs matches what the environment has to offer. It can be predicted and protected by knowing and supplying the light, moisture, nutrient and temperature levels of where the shrub, tree or vine grows natively.

Dr. Reich, syndicated farmdener (“more than a gardener, less than a farmer”) for Associated Press, describes why cold tolerant woody plants can or cannot be hardy. He explains cold hardiness in cold tolerant woody plants in the context of the freezing point of water.

Water freezes at 32 degree Fahrenheit (0 degrees Celsius) even though cold tolerant woody plants, whose interiors are filled with water, survive temperatures well below freezing.

Dr. Reich gives the example of woody plant cells that neither freeze nor rupture when boreal (northerly) temperatures drop below minus 150 degrees Fahrenheit (minus 101.11 degrees Celsius). Water has to have “something to group around to form ice crystals, a so-called nucleating agent” in order to freeze when it is expected to freeze. Nucleating agents include bacteria, whose suppression means that water will “supercool” in a liquid, not a frozen, form to about minus 40 degrees Fahrenheit (minus 40 degrees Celsius).

Proper moisture inputs and outputs juggle keeping just enough water from freezing inside cells and enough to freeze outside cells.

Permeable membranes keep water from freezing inside cells, where ice causes damage, so that destructive crystals only form outside the cells of cold tolerant woody plants.

Dissolved substances in the phloem flowing downward from foliage and in the xylem flowing upward from roots lower the freezing points inside cold tolerant woody plants. Water moves out through cellular membranes and into intercellular spaces so that the solution within cells becomes more concentrated and less respectful of water’s freezing point. The cold hardiness of cold tolerant woody plants needs permeable membranes and strong walls to remain intact but to resist dehydration, a greater danger than freezing.

Dehydration occurs when water does what it is known to do inside plants: go where it most will be needed.

Bonnie Appleton, Extension Specialist for Virginia Polytechnic Institute and State University at Hampton Roads, provides a list of “24 Ways to Kill a Tree,” excluding senescence. She questions the frequency of natural death and therefore refrains from including death by freezing on the list since “Few residential trees die of ‘old age.’”

Dr. Reich reveals that pruning without over-cropping, siting near paving and south-facing walls and winter swaddling, rosebush-style, encourage sugary cell sap and strengthen cell walls since “Light supplies the energy that plants need to prepare for cold, so we can make sure to site and prune plants so they get adequate light.”

Sugary, super-cooling, translocating agendas in hardiness zones or microclimates enabling pre-winter pruning and winter sunbathing support cold tolerant woody plants.

Plant processes for coping with cold include internal lowering of water's freezing point: Scotts Lawn @ScottsLawnCare, via Twitter Jan. 14, 2016

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Icy glaze encases tree. Despite cold challenges, healthy plants are able to survive and thrive; Wednesday, Dec. 12, 2007, 13:14: Ed Roberts, CC BY SA 2.0 Generic, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Ice_Storm_Kansas.jpg;
Ed Roberts (EdRobers), CC BY SA 2.0 Generic, via Flickr @ https://www.flickr.com/photos/52043848@N00/2106498688/

Plant processes for coping with cold include internal lowering of water's freezing point: Scotts Lawn @ScottsLawnCare, via Twitter Jan. 14, 2016, @ https://twitter.com/ScottsLawnCare/status/687675542846451712

For further information:

Appleton, Bonnie. “24 Ways to Kill a Tree.” Virginia Cooperative Extension Publication 430-210.
Available @ http://pubs.ext.vt.edu/430/430-210/430-210_pdf.pdf

Lee Reich.
Available @ www.leereich.com

Reich, Lee. 1 February 2016. “Plants Fend off Cold, to a Point.” Ottawa Citizen > Life.br /> Available @ http://www.ottawacitizen.com/life/plants+fend+cold+point/11692376/story.html

Scotts Lawn‏ @ScottsLawnCare. 14 January 2016. "Ever wonder how plants survive the cold?" Twitter.
Available @ https://twitter.com/ScottsLawnCare/status/687675542846451712