I'm researching temperate tolerant epiphytic orchids so it would be great if you could leave them all outside and let me know which ones survive! Then you could replace the non-survivors with other more hardy orchids and then you wouldn't have to worry about the cold... well... except for that blue moon super cold that occurs every 10 years.
If you don't want to sacrifice some orchids in the name of science I recommend researching minimum low temps for your orchids. By far the best resource for doing so is the
orchid culture website by the Bakers where for $1 you can purchase a comprehensive culture/climate sheet that contains average minimum temperatures by month for the orchid in its native habitat. Here are some
free example sheets
Or, if you know the latitude and elevation of the orchid in its native habitat you can calculate the lowest average minimum temperature by inputting them into this equation I developed...
Min = 77.35541724 - 0.838402676(Lat) - 0.003051964(Elev)
On average its off by 3 degrees... so to be safe add 3 degrees to the result.
Or, you could see if your orchids are on other people's outdoor growing lists...
Outdoor growing list for coastal Southern California
Outdoor growing list for Southern Australia (down to 23 degrees)
Outdoor growing list for Sydney, Australia (down to 32 degrees)
Summer time outdoor orchid list for the UK (displays country of origin and elevation range).
Santa Barbara Orchid Estate used to have a webpage that listed all their outdoor growing orchids but for some reason they took it off and only list a few
outdoor orchids. You can call them and they'll mail you their full outdoor growing list. It's quite extensive. You can also do a google search for
temperature tolerant site:sborchid.com to see all their temperature tolerant orchids. You can also do the same thing for
Andy's Orchids but with a lot less results.
Hope that helps!