Oncidium Pseudobulb turning brown at the base
 

I repotted this oncidium almost 2 weeks ago. I know I did it at the “wrong” time because there was no new growth, but I was really concerned about some black spots in a couple of the bulbs and a few of the leaves turning black and dying. So I decided to go ahead and repot it so I could take a look at its roots. I cut a fair bit of black mushy roots off, and the pseudobulbs with the black spots were also mushy at the very bottom, so I removed those as well. I worried about being too ruthless with it, but I also didn’t want to leave something attached that was rotting or had an infection that would spread. I put it in new medium (repotme’s oncidium mix with some sphagnum moss mixed in to help it retain moisture). Over the last week or so I’ve noticed this bulb turning brown at the base, and it’s slowly creeping it way higher. I’m really frustrated and concerned for the overall health of the plant; it’s my first and only non-phal and I don’t want to lose it. The brown area doesn’t feel super mushy, but it also doesn’t feel normal.

Should I take it out of the medium again and cut the rotten bits away? Should I wait until there’s new growth *somewhere* to do that? Please advise!!

It's hard to tell the extent of the infection, but I'd start by removing that pseudobulb, cutting away all of the discolored tissue, then carefully dab cinnamon on the wound with a Q-tip, being sure not to sprinkle the roots.

Thank you for your reply; should I take the whole plant out of the pot to do this, or is there a less traumatic way to go about it?

Oncidiums rot from the roots up. The usual causes are not enough air at the roots or being kept too warm. I doubt warmth is the issue here. Lack of air can happen with old compressed medium that stays wet too long, which closes the air spaces in the medium. The problem is lack of air, not water.

Oncidiums have very short rhizomes between the pseudobulbs. The rot spreads rapidly through the rhizome from the first affected growth. Typically by the time you first notice the rot the entire rhizome is affected and the plant is already dead.

I would take the plant out of the pot and use a strong jet of water to remove all old medium. Starting at the oldest pseudobulbs, cut off those that are soft and brown at the base, one by one. Sanitize your tool between cuts with rubbing alcohol or 10% household bleach. If you get to fresh green tissue at the base you can stop. This isn't likely. If you're lucky, let it sit for a few days in bright shade, repot, and hope for the best.

Sometimes all that remains healthy is an immature new growth. These sometimes will survive if they already have roots.

Sometimes all that remains is a pseudobulb that is mostly firm, with some soft brown areas at the rhizome. The new growth points at the base are usually dead when this happens, but there is another at the apex of the pseudobulb. If you wind up with a pseudobulb like this, set it someplace warm and dry and hope the rot stops spreading up from the base. If it does stop, after a week set the pseudobulb sideways on top of some barely moist sphagnum or vermiculite inside an enclosure - this can be a horizontal jar. The medium should not be moist enough for you to feel moistness but it should be enough to keep the humidity in the enclosure very high. Set it in bright shade. There is a chance the apical meristem will sprout a tiny new plant. This may take many months to a year or more.

Thank you so much for your response; I wish I had gotten here sooner to read it, but I must have missed the email. I got this plant in the beginning of January while it was in bloom. Over the course of a few weeks I started to notice a couple of the leaves were turning brown at the tips; someone suggested the humidity in the room may have been too low. Someone else suggested it may be fungal and to remove the leaves, which I did. I also got a humidifier just to be safe.

Despite both of those things, I still noticed the leaves continuing to die at the tips and decided that my best course of action was to repot it. I knew this was not best practice as there was no new growth yet, but I really wanted to see what was going on with the roots. Lots of them were mushy and rotted, as well as 2-3 pseudobulbs. I removed everything I saw to be rotten, and in the process the plant separated into two halves, which were repotted together. In hindsight I wish I hadn’t done that; I worry now that the rot has spread to the healthy half :( but I really thought I had gotten all of it.

The medium that was in it didn’t seem very degraded, in fact it always felt dry, almost like charcoal pieces. So I was watering it almost every day because I knew they liked to stay more damp than my phals. I also wonder if this contributed to the rot issues I was seeing. When I repotted it, I used RePotMe’s oncidium mix, with some sphagnum moss thrown in there to help me gauge how much moisture was in the pot and if it needed water. So I don’t think degraded medium is the crux of the issue, at least in the immediate case.

I’ll be repotting it this afternoon once my kids go down for a nap, so I can focus lol. I think my best hope is that the half of the plant that doesn’t contain the rotten pseudobulb was spared and has a fighting chance.

In the future… when I purchase an Oncidium from a garden shop, it’s typically going to be in bloom. Should I repot it immediately even though it’s not the “right time”? I’ve had this plant barely two months and it’s already on the verge of death; I don’t *think* I did all of that by myself in that short of time, I think it may have come home from the store with some issues and I just took too long to repot it and evaluate the situation. Or maybe I did kill it that quickly and need more information before buying another oncidium, who knows!

Anyway, thank you for your initial reply and any information you have in response to my situation. I really appreciate it!!

Thanks again,
Emerald