Lee Poulsen
Tue, 13 Jul 2010 22:53:40 PDT
> Good luck with Episcia: I don’t think I know another plant which is so cold
> sensitive. Outside during the summer they grow like weeds here. But as soon
> as the nights begin to cool off in the fall, the time comes (long before
> there has been any hint of frost) when they turn into a pile of mush.  
I used to think that Zone 10b was good enough for tropicals outdoors 
since this signified an average coldest night of the year above 
35°F/2°C. Of course there was always that once in a decade/century 
exception to worry about when the temperature might drop below freezing 
for one night, so to be more sure of this virtually never happening, 
Zone 11, which occurs in a tiny part of far southern Florida and an even 
tinier part of coastal southern California in the U.S. (not counting 
places like Hawaii and Puerto Rico). But then I tried growing the 
beautiful red sealing wax palm (Cyrtostachys renda/lakka) and discovered 
that there are some Zone 12 tropicals that simply won't survive 
temperatures below about +45°F/7°C or higher. It's as if that were their 
equivalent to what true 0°C freezing is for most other tropicals. Later 
I discovered that Episcia is also Zone 12. So I have to remember to 
bring it inside when my unheated greenhouse temperature starts dropping 
below 50°F/10°C at night. I have one or two other species like that, but 
can't remember what they are at the moment.

This information isn't accurately available very often I've found. Quite 
a number of plants that catalogs or books say to keep above 45°F or so, 
have no problems whatsoever with winter cold temperatures above 
freezing, especially if they're kept dry. Even more surprising to me in 
the past was how many bulbs from tropical areas have almost no problem 
surviving winters where the ground never freezes even if the air 
temperatures occasionally drop below 15°F/-10°C or lower at night, as 
can happen in the southern/southeastern U.S.

--Lee Poulsen
Pasadena, California, USA - USDA Zone 10a

More information about the pbs mailing list