Yes, you can grow a small mulberry bush in an outdoor plant box! Mulberries are adaptable plants that thrive in containers if given the right conditions. Choose a dwarf or compact variety like 'Dwarf Everbearing' or 'Issai' for best results. Ensure your plant box is at least 18-24 inches deep and wide to accommodate the root system. Use well-draining soil mixed with compost, and place the box in a spot with full sun (6-8 hours daily). Water regularly to keep the soil moist but not soggy, and fertilize lightly during the growing season. With proper care, your mulberry bush can produce sweet, juicy berries while adding greenery to your patio or balcony. Prune annually to maintain size and encourage fruiting. Container-grown mulberries may need winter protection in colder climates—wrap the box or move it to a sheltered area. Happy gardening!