I’m new to this and heard that growing bonsai in the ground will grow trunks much faster than in a pot. Because of this I decided to plant a small juniper into a large pot. Unfortunately, I neglected to try and find info if it was a good idea or not. My trees don’t look super happy right now, but it could also be a whole lot of other factors, too. I’d be happy to give more details or pictures, but I was mainly hoping to see if the large pot was the leading cause of their sadness or if it is a compounding factor. Thank you!

It is not a good idea to use a large pot, it will be too wet and cold, it is better to use the next size pot and repot regularly to next size up or plant in the ground. For every 5 years in a pot you will get the same growth in 1 year in the ground. Depending on when you potted them, the soil you used etc can effect the plants.

I do not concider too big pot beeing a problem. Wrong soil for the size of pot or tree, but not pot size in itself.

Yes, ground is always much faster than any pot. But bigger pot is also faster than a small pot.

Tropfrog wrote: I do not concider too big pot beeing a problem.  Wrong soil for the size of pot or tree, but not pot size in itself.

Yes, ground is always much faster than any pot. But bigger pot is also faster than a small pot.

I agree with this, but some time ago we had this exact same question and i lost the argument. I think the idea was that the large pot would produce root rot.

I have a tub abour a meter wide and over half a meter deep which i have used to transition from woods to bonsai pots more than once. The trees survived quite well. 

Actually it was a plastic tub that i drilled a hole in for drainage. Clay pots that large would be heavy.

Yes, big pot with wrong soil can generate root rot.