Did I overpot this dendrobium tobanese?
 

One thing I've been struggling with as a new grower is figuring out how big of a pot to use (for my non-S/H plants), especially dendrobium and cattleya alliance plants. Three months after repotting this plant I read some descriptions of the plant where folks say it absolutely must not be overpotted. Is the pot I have it in too big? If so, is it worth moving back down to a smaller size, or would disturbing it do more damage? In general, what are some rules of thumb for choosing pot size?

The plant in question:
(Please ignore the tilt of the plant caused by it growing towards an off kilter light over the past two months :D)

https://i.postimg.cc/8P6JF2yX/PXL-20...-180129673.jpg

That doesn't look overpotted to me. The real question is, how good is the drainage? The issue with "overpotting" is the center of the pot stays too wet. If the mix drains well, and you don't over-do the watering frequency (aiming for "damp" not "wet") it's not an issue. You just want to avoid the soggy-airless-center of the pot scenario. You can accomplish that with your watering frequency regimen. It looks like it is establishing new roots. I see no reason to disturb it.

plant does not look over potted but I question the stability of the support. The canes should be locked in firmly and standing upright with no wiggle at all. Any movement caused by flimsy support will not allow roots to attach to media as the root tips will scrape and stop growing.

Alright guys I'm back several months later...the plant is not doing great. It is about to bloom, but it has also dropped just about all its leaves. It has been semi-decidious in the past, but usually it keeps the current cane's leaves until the new canes start. This time it looks like its headed in the direction of having no leaves at all! Am I growing it too wet? Also, almost all of this year's new roots aborted. What should I do to save this plant? I would be very sad if it died. It was my first "serious" orchid.

It looks like the only good roots are the few newer ones at the top of the medium. Perhaps the plant has been struggling to take up water. They look somewhat deformed. That could be caused by the plant wiggling in the pot as the roots developed, or by thrips insects, which may nibble on roots.

I would not repot the plant now. That might damage the roots even more. I would suggest using a root stimulant such as Kelpak. Also stake the plant so it can't wiggle, and perhaps use a rhizome clip too. New roots will help a lot.

Yeah, the deformed roots from instability theory makes sense. I have a problem with tall plants in this small-ish orchiata. Plants that grow roots vigorously and stick to the side of the pot like paphs and coelgyne seem to work because the roots go down so quick and are so sticky. But my dens I have in this have not done as well. Staking seems to only go so far, as even the stake is not super well anchored. So here's what I'm thinking of doing. Kelpak is on order. I will apply it when I get it. When/If new roots start coming out, I will stake and re-pot into the same size pot, but a size of orchiata larger, which just fits together better and holds the plant better. Here are my questions with this plan:

1. Will a size larger bark make this plant grow too dry? I can't seem to figure out how wet or dry to grow dendrobium tobanese.
2. Will Kelpak at this time of year / growing cycle mess with the plant?

I think that you will find that it's harder to "anchor" plants in large bark than small, especially in a small-ish pot... the stakes don't stay in place as well. When I have a tall plant that is hard to stabilize, I supplement the stakes with "guywires" - poke 3 holes in the plastic pot evenly spaced, and then tie the plant to each. Just as a tripod is stable, the 3 ties pull against each other, making a stable configuration.

I would not repot this plant now. I agree larger bark is more wobble prone.