Hi there, I am looking for a tree, preferably evergreen that would be suitable to plant in a half barrel.

Great idea Mara. Whatever you choose ensure you put the best possible potting mix into the barrel (we suggest Tui Pot Power), and that you have good drainage holes.

Reliable options are, evergreen magnolia - Little Gem, Michelia species, Lily Pilly – shaped into a topiary, standard buxus, or Portuguese Laurel. Kowhai, Karaka and Lacebark are nice native options.