I currently have 4 half wine barrels each planted with a dwarf columnar apple tree, 2 chive plants, and an herb (2 have rosemary, 1 has thyme and lemon balm, and the other oregano and lavendar). They have been going strong for about 3 years now and produce pretty well, but I would like to add a perennial nitrogen fixer for a bit of soil health. I'm in Zone 8 and have looked at adding licorice (Glycyrrhiza Glabra), Huang Qi (Astralagus Propinquus), or even AlfAlfa, but I am a little concerned that they might not have enough space to grow. Any suggestions? If this is the wrong forum my apologies.