The hardiness temps from Phillips and Rix are a perfect example of why
climate factors other than temperature are so important. -25°C/-13°F
is ridiculously tender for versicolor, considering it's native at
least as far north as Zone 3a (-40°C/-40°F). For that matter, I'm not
sure versicolor is even native as far south as their estimate would
imply (Zone 5b). At least some of the other temps are way off for a
continental climate as well.
Sean Z
Quoting Diane Whitehead <voltaire@islandnet.com>:
> Debbie's information about Alaska is interesting.
>
> One other variable is timing. Usually our temperatures gradually get
> colder and plants fortify themselves for the winter. Occasionally we
> will get an arctic blast while everything is still in full growth. I
> can remember a fall when the trees hadn't turned colour yet - their
> leaves were still green, and got frozen onto the branches so we had
> brown-leaved trees all winter.
>
> In England, and perhaps other European countries too, gardeners worry
> about spring frosts when plants have begun growing again.
>
> I agree with those who said we should note the plants that grow well
> in our normal conditions.
>
> It is reassuring to have a reliable source of information about
> hardiness. The usual U.S. zone information is not very helpful to me
> here on the Pacific coast.
>
> One set of books that I have found consistently reliable is by Roger
> Phillips and Martyn Rix, published in the U.K. Their numbers may not
> be at all helpful to those of you with a continental climate, but
> perhaps they might. You may find it helpful to look at their
> recommendations for plants you are very familiar with, to see if you
> can trust them with advice about plants that are new to you.
>
> For my conditions, if they say a plant is OK at -15 C (5 F), the
> plant will be completely hardy, at -10 C (14 F), it will live most
> years, but get killed in a bad winter which happens perhaps every ten
> years or so.
>
> I see I should not have been growing confusa outside. I didn't check
> first.
>
> Here are a few samples of iris from their book Perennials Volume 1:
>
> confusa: -5 C 23 F
>
> clarkei: -15 C 5 F
> delavayi: -15 C
> wilsonii: -15 C
> lazica: -15 C, leaves killed at -10 C
> unguicularis: -15 C
>
> cristata: -20 C -4 F
>
> setosa: -25 C -13 F
> versicolor: -25 C
>
>
> Diane Whitehead
> Victoria, British Columbia, Canada
> maritime zone 8, cool Mediterranean climate
> mild rainy winters, mild dry summers
>
>
>
>
