Instinct Check: too much humidity?
 

Hey y'all. I have an oncidium (fka wilsonara) Firecat 'King Snake' that a friend gave to me as a rescue. It was in very bad shape when I got it, no live roots, lots of rot and mildew in the pot, some bacterial infections on some leaves. I have it potted in a 3-inch pot with Monto Clay only. It has one small new growth chugging away. AFAIK it has only one small, short root on the new growth.

I had it in medium light, but I moved it into lower, indirect light because the older PBs were shrinking hard, and with only one root I was concerned it couldn't keep up with the moisture needed by photosynthesis. It seems to grow in fits and starts. I thought maybe it needed more humidity, so I set the pot in a large vase with leca and water in the bottom. Not touching the water, uncovered, etc. It's been in there about a week and yesterday, the remaining "sheath leaves", the first outer leaves, turned black. The tip was dryish but the base was wet. I've pulled off as much of the black as I can and sprayed it with Listerine.

Am I correct in thinking that this means it was too humid inside the vase? I'm wondering if I should put it into the vase but move it into a dryer, high-light position, or keep it out of the vase in this low light place.

No, that was not caused by "too much humidity", unless there was condensation that accumulated there.

Your instinct to raise the humidity was a good one, though. With only one root, transpirational losses were outstripping the plant's ability to absorb enough to keep up.

More likely a lack of air movement. Humidity and air movement are closely linked, and I would bet that if that plant was in a well run greenhouse that ran the same humidity but had good air movement it would be on its way to recovery.

Oncidiums only make new roots from new growths. A plant such as you describe needs to survive long enough to make a new shoot and accompanying roots. If it reaches that point on it will probably live.

Many people, upon finding an Oncidium with few roots, unpot it completely and set it in an enclosure, on top of a little just-damp medium, and keep the humidity as high as possible. You're trying to buy time in a race between death by dessication versus making a new growth that can absorb water.

Members of our society have also revived such plants by cleaning off everything dead, then sitting them in an inch of water in a vase. They change the water frequently so it doesn't stagnate. You can look up "full water culture."

Another issue is temperature. I'm not familiar with this hybrid. Some Oncidium hybrids are not warmth tolerant. When they're hotter than they like they decline and die in the manner you have described.

I see that I didn't specify in the original post that the leaves turning black were on the new growth, which is very tiny.

I agree that the symptoms do sound like lack of air movement. But I dismissed that because a ceiling fan runs all day. Lately the humidity has dropped so I have been trying to add a little more in every way I can.

I ended up unpotting it (I had to, one of the older bulbs had been drained and was getting mushy so I needed to cut it off) and found that the original root had not grown any, and there was one small new root. In the process I discovered that over-fertilization was probably the culprit. I don't know how this happened but there were WAY too many prills in the pot. I obvs made a mistake when I added fertilizer. So I sorted and removed all of them.

Then while putting it back into the pot, I managed to break off the new growth. Argh. The two roots are still attached to the rhizome and there are two remaining PBs, so I'm hoping it will do okay. I flushed the medium and will wait for it to make a new new growth.

Thanks for all your comments!