Harry Lauder's Walking Stick

Bought a nursery Harry Lauder's Walking Stick. Has buds that have not opened.
How aggressive can the branches & roots be pruned; enough to plant in a
bonsai pot? Thanks!

They are rather fickle in my experience, especially if they are not grafted.

I would recommend only one harsh action per season, assuming it recovers well. As you don't know it's recent history and have just shelled out cash for it I'd say do nothing for at least a few months. In mid summer perhaps post some pics showing how it is looking.