Q. My Oncidium has wrinkled pseudobulbs. Help!
Thank you for your question. First off I wouldn't repot while it is in full bloom. Regarding the pseudo bulbs pleating, here's what I found:
Oncidiums and their relatives like a freely draining potting mixture. Let the pot dry before watering again, checking the condition of the lead pseudo bulb or fleshy leaves for signs of hydro-insufficiencies. The lead bulb and the two behind it should be plump, and mule-ear and equitant leaves should look reasonably plump and unwrinkled. In most species, the new growths produce numerous wiry roots as they mature, so divisions recover quickly if you time repotting correctly. Pleated foliage is less common among Odontoglossums or Miltonias, but if you see pleating, it could be the result of low humidity (not being in a greenhouse) or a buildup of sticky exudates that some plants secrete from developing leaves. I’m voting for low humidity, since home interiors are pretty dry, really dry, unless you have a humidifier going. In addition, older pseudo bulbs will pleat somewhat. If it is the sticky problem, you can give it a lukewarm ten-minute shower only every few weeks during its vegetative growth spurts.
Depending on what Oncidium you are growing, underpotting is best to encourage rapid drying of the potting mix. Btw, what kind of potting mixture is in the pot. What kind of pot, plastic or terracotta?
More here from American Orchid Society http://www.aos.org/orchids/culture-sheets/oncidium.aspx
Hope this is helpful.