Pot size for miniatures in S/H

[svlair]

I recently received four new Oncidiums and transferred them to S/H. An Oncidium Tsku Marguerite and Oncidium Hulu Halau Volcano arrived in 3" pots and were transplanted into Ray's 4.5" S?H pots. These are doing well.

Two miniatures, Oncidium cheirophorum and Oncidium croesus, were in 2" pots and were transferred to homemade containers from clear plastic drinking cups with drainage holes 1" from the bottom.

The miniature Oncidiums are suffering after two weeks in S/H with one third to one half of their leaves yellowing. I have transferred them to 4.5" pots and moved them to another shelf with less light in hopes of saving them.

Is there a minimum pot size for miniatures? I think they were drying out excessively and/or the reservoir size was too small. I believe the roots were staying above the dry line in the smaller containers even with daily watering Any feedback would be appreciated.

Growing conditions: Daytime High temps 84F, humidity 45-50%, ventilation from 6" clip on fan, 2200 foot-candles 12" from four T5 HO bulbs, 14 hour day length, 50 ppm MSU fertilizer with each watering.

[OhioBob]

I can't speak for the species you are asking for but it is really important that the plants have actively growing roots when you put them into S/H. The old roots will not do well in transitioning to S/H. A year ago I moved several Oncidium plants (all NOID) to S/H in the hopes I could get them to flower and they were in various stages of growing roots. The weakest plant with very little new root growth eventually died but the ones with a lot of root growth did great.
The exception to this rule, I noticed, is if your plant has lots of aerial roots. These will do well and will grow actively in the pots.
the roots should be above the water reserve. If the top half inch of LECa is drying out too much I suggest adding a layer of spagnum to the top of the pot to slow drying out.

[svlair]

Strangely enough the miniatures had the best aerial roots of the four. I believe the containers were too narrow and too tall for these small orchids. They are doing better in larger but shorter pots. I believe the wicking action of the media was not reaching the roots. Too soon to see if they recover but the yellowing of the leaves has not progressed.