Dwarf citrus will do well in a half a wine barrel. The barrel will rot away about the time you will need to replace the mix anyway, and if you prune the roots and use new mix you will be good again. Al

Spray the interior of the barrels with water seal, one of the more safer formulas and let dry as the barrels will last longer. Or oil them to season the finish. They will rot slower and not disintegrate as I have had happen to me. I have a huge barrel over an odd manhole in my yard in the woods that has huge jade plants volunteered in it. It is still doing well going on ten years now.