From: pharvey@quack.sac.ca.us (Paul Harvey)
Subject: Re: List of cold climate gums
Organization: The Duck Pond public unix: +1 408 249 9630, log in as 'guest'.
	<fVnEMwN@quack.sac.ca.us> <1992Nov18.232915.8173@sserve.cc.adfa.oz.au>
Date: 19 Nov 1992 05:53:37 UTC

In article <1992Nov18.232915.8173@sserve.cc.adfa.oz.au> 
rim@csadfa.cs.adfa.oz.au (Bob McKay) writes:
>pharvey@quack.sac.ca.us (Paul Harvey) writes:
>>I've added temp data from Sunset Guide to Western Gardens and HortusIII.
>>As you can see, it don't get all that cold in Oz.
>I found these fascinating, partly because they're inconsistent in some 
>significant cases with my own experiences. It may relate partly to the 
>particular clones that are used in the US (you have some particularly 
>beautiful forms of some of the dry country Eucs that I haven't seen here). 
>I've annotated below the ones that seem problematical to me - any comments?
>(I've expressed my opinions fairly baldly below, but they should be read in
>the context of the above disclaimer about clones - I just don't want to have
>to keep repeating it)
>>>E. pauciflora           Snow Gum		10-15oF
>This species is very variable, but there are certainly forms that can go 
>colder than this.
>>>E. stellulata           Black Sally		12-18oF
>This is one of the two most cold tolerant gums I know of. I don't have any
>temperature data handy (though I'll try to check it out tonight), but I find
>these limits hard to believe (and unlike the previous species, it's hard to
>explain it in terms of species variability, since it's not one of the more
>variable species)
>>Sunset also has the following "hardy" gums:
>>E. macrandra	Long Flowered Marlock	8-12oF
>This seems optimistic, though I don't have actual data
>>E. niphophila	Snow Gum	0-10oF
>This is believable.
>>E. rhodantha			8-12oF
>>E. sideroxylon	Red Ironbark	10-15oF
>These are the most problematical for me. Around Canberra, sideroxylon appears
>to be temperature limited (as a wild species) and rhodantha is difficult even
>as a protected garden specimen. Contrast this with pauciflora and stellulata
>above, which grow quite happily in the wild, 3000 - 4000' higher and can't
>compete around Canberra (minima around 20F screen, 13F grass). The rhodantha
>value is particularly surprising - if there really are varieties of this
>superb small tree that can tolerate such low temps, they would be worth a 
>small fortune in the local horticulture trade here (but I guess I could never
>get them through quarantine)

Well, it would be foolish of me to argue about the cold hardiness of
gums with someone who lives with native wild ones, but, I do have some
comments nonetheless. If I'm not mistaken, Canberra is around 35o
lattitude which puts it about the same spot as Los Angeles, so that's
more or less equivalent. But, California has a Mediterranean or modified
Med climate and is exposed to occaisional hard freezes from Alaskan air
mases that Canberra is not. So, point one is that the gums in Cali are
probably selected as the most cold tolerant of their species. Point two,
I would guess that botanists in Oz know more about Eucs than botanists
in Cali, so what are refered to as species such and such in the US may
not actually be the same species in Oz although I would tend to doubt
that since the Eucs are a well studied genus. Point three, wild species
are not always limited in their wild range by temp minimums. Often a species
or botanical variety can be grown well outside its natural range, in
cultivation. Point four, it's possible that natural preditors limit cold
tolerance in Oz and are not present in Cali. Point five, maybe you ought
to look into importing some of those cold hardy Cali Rhodantha's. Well
that's about all the excuses I can come up with, maybe someone else has
some more theories of why the discrepancy. The numbers I quoted were
from Sunset Gardens Guide to Western Gardens which is a fairly reliable
reference. Oh, one more variable I just thought of, snow cover. Reliable
snow cover would be rare in most Cali Euc areas whereas this may not be
the case in Oz. And one more [this is kind of by the seat of the pants
here, can you tell] : Hard frosts in Cali are almost always radiation
frosts on clear still nights. Windy cold fronts and cold snow storms are
pretty much unknown.
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