In our Sunnyvale garden, half of the trees are in pots. We simply do not have the ground space for more trees. In the 100 foot by 2 foot side-strip we have gingko, tangerine, grapefruit, feijoa, pomegranate, apricot, orange, and lemon. In the former swimming pool is a large cherry tree. In the former hot tub is another apricot tree. The rest of the trees (Mission Fig, Tiger Fig, Lime, Australian Finger Lime, Mulberry, Pear, Plum (x4), and Cherry) are in pots. Some of the trees are grafted onto ultra-dwarf rootstock to satisfy two requirements: limited pot size and limited tree size.
Despite of, or in spite of, the well-laid plans of a gardener, the tree roots continue to grow. Our 12 year old Weeping Santa Rosa plum was producing few fruits and even few new growth of branches and leaves. As you can see in the photo, the rootball is completely root-bound. The diameter is the size of the pot.
Into the old tall pot goes Chinese Lantern Abutilon with seasonal pansies trailing over the edge.
As for the old tree, I hear plum wood goes good in a smoker.