Jim, I completely agree with you about the effect of humidity on hardiness. In my part of Idaho we have very hot, extremely dry summers and moderately cold dry winters with snow cover perhaps 15% of the winter or less---average precipitation is around 12 per year almost all of which comes in winter or very early spring. Fortunately, we have little wind and this helps keep desiccation and winter burn down to some degree on exposed plants(think: Dasanthera penstemons) . Dry as it is we can still grow eastern orchid species such as these:
http://photos.imageevent.com/teita/spring06rockgardenplants/websize/DSC00009 .JPG http://photos.imageevent.com/teita/spring06rockgardenplants/websize/springla te%20001.jpg http://photos.imageevent.com/teita/gockgardenmay252010/websize/spring%20orch ids%20007.jpg then there are the Chinese species: http://photos.imageevent.com/teita/gockgardenmay252010/websize/C.%20macranth um.jpg All of them require a bit of pampering when it is 108F out and 20% humidity! Jim Hatchett Eagle Idaho zone 5 From: [email protected] [mailto:[email protected]] On Behalf Of Jim McKenney Sent: Thursday, February 10, 2011 11:16 AM To: 'Alpine-L, the Electronic Rock Garden Society; postings copyright by authors.' Subject: Re: [Alpine-l] Orchids in winter Jim Hatchett wrote Yes these zone are confusing to me as well. I know nothing about the climate of Idaho, but Im guessing that its drier than Maryland in the winter (or under snow). Many plants which are adapted to very cold but dry winters are, in terms of zone hardiness, much less hardy here in the east. As an example, Hesperaloë parviflora is marginally hardy here in zone 7, but properly sited it does very well. Many of the Agave are rated for much colder zones than our zone 7, but they are dubious garden plants here for the most part. And yet, every once and a while someone has a spectacular success with one. It was a real eye-opener to see the hardiness ratings for agaves in the wonderful High Country Gardens catalog, and I trust their ratings for their climate. But those of us in the east have to take these with a grain of salt (and find suitable microclimates if we want to give those plants a try). Jim McKenney
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