If you're considering growing a small zelkova tree in an outdoor plant box, the answer is yes—with some important considerations. Zelkovas, particularly the Japanese zelkova (Zelkova serrata), are adaptable trees that can thrive in containers if given proper care.

Key Factors for Success:

1. Box Size: Choose a spacious plant box (at least 24 inches deep and wide) to accommodate root growth. Dwarf or young zelkovas are best suited for containers.

2. Drainage: Ensure the box has drainage holes to prevent waterlogging, which can harm the tree.

3. Soil Quality: Use well-draining, nutrient-rich soil mixed with organic compost.

4. Sunlight: Zelkovas prefer full sun to partial shade—place the box in a spot with 6+ hours of sunlight daily.

5. Pruning & Maintenance: Regular pruning helps maintain shape and health, especially for bonsai-style zelkovas.

Long-Term Care:

- Repot every 2–3 years to refresh soil and prevent root binding.

- Water deeply but infrequently, allowing the soil to dry slightly between sessions.

- Protect from harsh winters by moving the box to a sheltered area or insulating it.

With attention to these details, an outdoor plant box can be a great home for a small zelkova, whether as a patio centerpiece or a bonsai project.