Alicia Moïse wrote:
Live in central OH and keep several vandas in my conservatory on a humidity
tray. The leaves turn yellow and fall off then it dies. What else do they
need? Dendrobiums, cattelayas, phalenopsis live in the same room and are
thriving. Varigated papheopedolums have healthy foliage but don't bloom.
Any suggestions?


I also live in central Ohio and grow indoors during the winter, in three
growrooms; my humidity is usually too low there. You don't say how much
light the vandas are getting or in what/how they are potted. I grow mine
potted in plastic pots with large bark mixed with sponge rock #4 (the
largest I can get) and water them as often as everything else, usually
every 4/5 days or so. They sit immediately under the 400W light.
I have even bloomed a few:

http://www.orchidcourt.com/vandpics.html

Perhaps yours aren't getting enough water. Vandas are actually
waterloving plants; they just don't like to be too wet around the roots
at night.

Don't know if you're a member of the Central Ohio Orchid Society

http://www.coosinfo.info/

but there are a lot of long-time growers there who are more than happy
to help out with whatever insight and experience they may have, and even
more newer growers full of excitement and questions.

Of course there are other possible problems: thrips, disease, etc. Hard
to say for sure without more info and seeing the plants.