Question
Do dendrobiums, cattleyas, oncidium, and vanda survive the winter when night temperature drops to about 30F?  I live in downtown San Jose.  Will dendrobiums' leaf falls when the temperature falls below 40F?  What kind of winter protections I should have when the winter temperature drops to about 30F?

Answer
Hello Alex,

Hey, we're almost neighbors, I live in south San Jose.  

The answer to your question is "yes and no".  Whether they are capable of surviving 30F depends upon what type of species are in the background of your orchids.  While most of these do not like temperatures much below 50F, there are a few species in each type that originated in areas that have cool winter climates.  

Many of the deciduous dendrobiums can survive cool temperatures when kept on the dry side.  Cattleyas with a strong sophronitis (look for those with the letters SLC in front of the orchids name) influence can survive if kept somewhat dry.  I'm not certain about the types of oncidiums and vandas but I believe there are some types than can withstand the cold for short periods.  

As for your question about dendrobiums losing their leaves below 40F, the deciduous kinds will do that but the evergreen types may lose their leaves but also they may lose their growths or canes if temperatures go much below 35F.  If you are uncertain about what type of dendrobiums you have, basically if the flowers were on spikes near the top of the canes they are of the evergreen variety but if they grew along the canes then it probably is a deciduous type.  

Other than the deciduous dendrobiums and SLC cattleyas, it would be best to move the others indoors once night temperatures drop below 50F.  Also, with most of our rains occuring in winter, it would be a good idea to provide overhead protection for the ones left outside to keep them on the dry side.  

Hope this helped.  

Jim Kawasaki
San Jose, Ca.