Need a tree

The diameter of the pot depends on how much you want it to “spread”. The depth, I don’t know but I’d say as deep as possible because the roots will fill the pot and it will dry out more quickly if it’s shallow. Likewise plastic would be better than wood.

We have three bamboos in the garden, all filling in gaps where other plants won’t grow. Two are in 70 cm tall by the same across pots and block the views of the cat litter “shed” and log store. The one in the photo is filling in a gap between the garage and the boundary wall. It’s been in this broken plastic pot for about three years.