When repotting root bound orchids, do you break up the root ball?
 

I am repotting my oncostele that is very rootbound. The old moss is tightly packed in the roots so I just stuck it in a 1” larger pot and added new media to fill the sides and bottom. Am I supposed to break up the root ball or leave it alone?

It depends... If the old moss is in decent condition, yes just leave it. If it is starting to look broken down, you can just wash out the bad stuff with a hose. But as long as roots look good, best not to disturb them until the plant is big enough to divide. Oncostele and other members of the Oncidium group want to stay on the damp side, so as long as the moss drains well, staying wet isn't really a big issue. If you see a lot of rotted roots, then you'd want to clean them up. But it sounds like a plant that is doing well.

Yes this one was in a 4” pot and I moved it to 5”—I kinda got a little overeager and ended up breaking it up 😅 I stuck it in the new pot and tried to fill in as best as I could but it was difficult on the sides so there are some gaps there. Hope it isn’t too unhappy with me...

I don't break up root balls. I might use a stream of water to flush out what is loose.

as you can see growers have different approaches to this. I break up the moss. Soaking it overnight in a bucket of water helps otherwise you might do some damage.
You can leave it but you never know what is in the center of the moss, too often have I found a jiffy plug in the center which soaks up far too much water and just causes the plant to degrade down the road.
You can leave it and hope for the best but if it does degrade then it will be too late.
On the other hand if roots get damaged during a repot then the plant will be set back months.
So it's a bit of a dilemma between taking it out of the previous growers substrate to replace with ones own and risk stressing it or leave it, not stress it but risk it rotting because the substrate goes bad.

I’m with Orchdtinkerer on this one.