Can you please tell me the size of stone I should be looking to use, at the bottom of the pot, to help with the drainage?
Can I use pebbles? I am afraid of going to small or too big and/ or picking something that would be bad for the trees/bushes.

Thanks,
Lisa

You fill the pot with the substrate. No rocks on the bottom. If you need something to cover the holes in the pot, fine netting is used for this iwith tipycaly 2mm holes in it.

I was told I needed stone in addition to the screen.
Thanks,
Lisa

Thanks. I thought I needed both.
I am glad I don't
Thanks,
Lisa

Skye wrote: I was told I needed stone in addition to the screen.
Thanks,
Lisa

A bonsai pot is (or should be) already a very limited space for the roots. You don't want to take some of that away with stone(s).
Use decent bonsai substrate, alone, and you'll be fine.

Skye wrote: Can you please tell me the size of stone I should be looking to use, at the bottom of the pot, to help with the drainage?
Can I use pebbles? I am afraid of going to small or too big and/ or picking something that would be bad for the trees/bushes.

My first book said to use a piece of broken pot to lay over the hole to keep dirt from draining through the hole. That was a long time ago.

A couple of years later a book said to use a flat stone, so this is advice that was good once, but should have faded into oblivion long ago; In today's world, a piece of screen of some kind. I used to use plain old window screen, but with online ordering you can get pieces of plastic screen pretty cheap.