Rotten pseudobulb on oncidium (right)
My Oncostele Pacific Perspective lost another pseudobulb yesterday. Although it still had green leaves attached, the bulb had turned mushy and had to be excised. This is the second pseudobulb to rot since it rotted its last one in May. I am not sure what's causing this rot. Generally orchids rot when there is too much moisture that is not drying out. But if anything, I haven't been watering enough; the leaves on the newest growths are wrinkled from dehydration.
My guess would be that these problems arise from the orchid not having enough roots. With its many old pseudobulbs, the orchid would not fit into any pot small enough to be appropriate for its root size. As a result, the media would be both too dry near the top where many of the new roots were growing, and permanently soggy elsewhere, leading to bulb rot.
Oncostele Pacific Perspective
Once again diminished, the oncidium is now in a 4 inch clear plastic pot, with loosely packed oncidium potting media. There is a good amount of new root growth, which will hopefully support the two new growths as they mature.