Why can't some trees/plants survive frost? All about roots?

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Monolith Holyoke, MA Apr 18, 2010

What's the reason that many trees/plants can't survive outside during the winter? Is it that the entire plant (foliage and all) can't be frozen? Or is it mostly that the roots alone can't survive being frozen?

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altagardener Calgary, AB(Zone 3b) Apr 18, 2010

Well, with respect to trees, it's pretty clear that a species that is not even root-hardy (i.e. not even the roots underground can survive the cold) has no chance of survival in a climate colder than it's adapted to. If we look at a slightly hardier species, one whose roots can survive due to the protection given by being underground, it will never be able to take on anything like its normal form (appearance) if the top growth is killed to the ground every year, or every few years. In other words, it's possible it will never be able to exist as a "tree" (a plant that has woody above-ground growth that remains from year to year), or as a tree with the desired ornamental characteristics.

Perennials are much more forgiving in general; so long as they are root-hardy, you have a chance.

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ecrane3 Dublin, CA(Zone 9a) Apr 18, 2010

Here are a couple links with some more explanations of how cold kills plants
http://www.thisgardenisillegal.com/2006/10/not-so-cold-hardy-killers-why-cold.html
http://www.richmondnursery.com/index.php/gardening-articles-mainmenu-30/1-gardening/88-does-cold-kill

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altagardener Calgary, AB(Zone 3b) Apr 18, 2010

And, finishing off... Perennials are more forgiving because they can regenerate from the root. Many are herbaceous in nature, meaning that they will die to the ground in winter under normal conditions, and then regrow from the root... you can see how this would probably be a tremendous advantage for survival over a wide climatic range. Even ones that are evergreen in warmer climates may survive in colder climates by regenerating from the roots.

As to why some are hardy and some are not... it's due to evolution of the plant species and its adaptation to the changing cimate in which it existed through time. Many plants currently have natural ranges that are in much warmer climatic zones than the plant is actually capable of existing in; its cold hardiness is a relict of conditions it survived earlier in the species history. The South African species (e.g. from the Drakensberg) that are hardy down to zones 3-4 are an example of this; the area currently never experiences climatic conditions like those in zones 3-4, but it did during ice age periods in the past, and the relict hardiness of the plant species reflects it.

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