Yes, you can grow dwarf coffee plants in an outdoor plant box, provided you meet their specific needs. Dwarf coffee plants, such as Coffea arabica 'Nana,' are compact varieties ideal for container gardening. Here’s how to ensure success:

1. Choose the Right Plant Box: Select a sturdy, well-draining container at least 12-16 inches deep to accommodate the roots.

2. Sunlight Requirements: Place the box in a spot with bright, indirect sunlight or partial shade, as too much direct sun can scorch the leaves.

3. Soil and Watering: Use acidic, well-draining soil and keep it consistently moist but not waterlogged. Mulching helps retain moisture.

4. Temperature and Humidity: Dwarf coffee plants thrive in warm climates (60-75°F) and high humidity. Protect them from frost or extreme heat.

5. Fertilization: Feed with a balanced, slow-release fertilizer every 2-3 months during the growing season.

With proper care, your dwarf coffee plant can flourish outdoors, even producing aromatic flowers and small coffee cherries over time. Happy gardening!