Question
we live in connecticut and have been having good luck with our phalaenopsis plants but not so hot with our oncidiums.  We have them in a west exposure in a small room.  I recieved them  as a gift and they were in a small pot and appeared root bound. We have not been able to get them bloom again.  How large a pot should we use to repot them and should we use bark or sphagnum moss?  The leaves are wrinkled even after lots of watering.  Help...

Answer
Hello Maureen,

As you are finding out, oncidiums are not the same as phalaenopsis orchids.  One of the major differences between them is that oncidiums need more sunlight in order to grow and bloom than phals.  Oncidium leaves should be a light green color (even yellowish-green) when recieving proper light levels, if yours are a medium to dark green color then it is growing too shady.  Move it slowly towards more sunlight over the next month to prevent shocking it.  

If the oncidium is potbound with new growths close to the pots edge, repotting may be in order.  If you repot it, use a pot that is slightly larger than the current pot.  Oncidiums like to have their roots somewhat confined, so it is best to put it into a pot size that will barely hold the roots.  My recommmendation for potting material would be small size orchid bark rather than sphagnum moss.  S. moss tends to hold and retain too much water and takes a long time to dry out which can cause the roots to rot.  Oncidiums prefer the potting mix to become barely moist between waterings, constantly wet mix will drown the roots.  

Wrinkled leaves is usually an indication that at some point the plant had been very dry for an extended time.  Once the leaves are wrinkled they will never straighten out, if it really bothers you, cut them off.  

While a west exposure window is fine, your oncidium would be happier in a southern exposure window.  One problem with the west window is the amount of heat in the afternoon, if the leaves feel warm to the touch they are on the verge of being sunburned.  Living in Connecticut, you probably could grow the oncidium in full sunlight in an easterly facing window all morning.  

I hope this helps.  Good luck and good growing.  

Jim Kawasaki
San Jose, Ca.