I bought what looked like a dead branch in a pot last year from a farm market...this year it has leaves, is lovely and I am told it is a walnut tree. Now, it's still quite small and is also in a small pot. When is the best time to move it into a bigger pot and is there anything special it requires? And is it realistic to hope to keep it as a potted tree? I only have a covered balcony as a garden, no yard....
JMO, but it would probably be better to plant the tree outdoors in the ground. IIRC, walnut trees (and also oak trees) have long taproots, and wouldn't do well in a container.
I have a huge Black Walnut tree they are nice for shade but as I am learning not nice for many other things to be around. If you decide to give this tree away or plant it somewhere make sure you read up on the type of walnut you have. https://www.ext.vt.edu/pubs/nursery/430-021/430-021.html