Yes, you can absolutely grow a small hydrangea in an outdoor plant box! Hydrangeas are versatile plants that thrive in containers when given the right conditions. Here’s how to ensure success:

1. Choose the Right Variety: Opt for compact or dwarf hydrangea varieties like 'Little Lime' or 'Bobo,' which are well-suited for confined spaces.

2. Select a Spacious Plant Box: Ensure the box is at least 18-24 inches wide and deep to accommodate root growth. Proper drainage holes are essential to prevent waterlogging.

3. Use Quality Soil: Hydrangeas prefer rich, well-draining soil with a slightly acidic pH. A mix of potting soil, compost, and perlite works well.

4. Provide Adequate Sunlight: Most hydrangeas need morning sun and afternoon shade. Avoid placing the plant box in harsh, direct sunlight all day.

5. Water Regularly: Keep the soil consistently moist but not soggy. Container plants dry out faster, so check moisture levels frequently.

6. Fertilize Wisely: Use a balanced, slow-release fertilizer in spring to support healthy growth and vibrant blooms.

With proper care, your small hydrangea will flourish in an outdoor plant box, adding beauty to patios, balconies, or garden spaces. Happy gardening!