All containers need good drainage, especially if they are on the tall side. The wood planter to the left will have pea gravel in the bottom 2/3rds. For a tree, the middle third would be half gravel and half soil.
Great drainage means lots of water [galvanized liner] and loss of nutrients quickly. The soil on the top third will have to be changed yearly to maximize plant health.
Look for the finished photo next week!