Quite often I'll come across a species description that includes county of origin and elevation but neglects to mention minimum temperature tolerance...which is a fairly significant factor in deciding which orchids to try to grow outdoors in nearly frost free areas.

It's been around 10 years since I took a statistics class and math was never my strong point but I googled around and found out how to create a multiple regression equation using excel that would predict the lowest average minimum temperature of a species based on elevation and latitude.

For example, let's say that there was an epiphytic orchid native to my hometown of Glendale, CA (I wish) and I wanted to figure out the lowest average minimum temperature that it was subjected to... I would find out the latitude and elevation...

Lat = 34
Elev = 256

and input it into the following equation...

Min = 77.35541724 - 0.838402676(Lat) - 0.003051964(Elev)

Min = 77.35541724 - 0.838402676(34) - 0.003051964(256)

Min = 77.35541724 - 28.505690983999997 - 0.781302784

Min = 48.068423472

So basically the lowest average minimum temperature for my local orchid would be 48 degrees. The website I used to figure out my Lat/Elev and double check my lowest minimum was (source). To create the equation I used the climate data for 394 northern hemisphere occurring epiphytic orchid species.

Out of the 394 entries one prediction was off by was 22 degrees. But the average degree difference between the predicted and actual was just under 3 degrees. The difference between the actual and predicted temperature is most likely due to maritime influences. So if the orchid is near any large body of water than the predicted temperature should most likely be higher. Please feel free to post how accurate it was for your location. If there are any math people out there who would be interested in double checking my calculations let me know and I'll e-mail you the Min/Lat/Elev data.

Obviously, there are numerous factors in selecting orchids that are suitable for growing outdoors year around in your area. The above equation should most definitely not be used as the sole determining factor.