Creating a formal garden with an outdoor plant box requires careful selection of plants that exude elegance and structure. Here are the top choices to achieve a polished look:

1. Boxwood (Buxus sempervirens) – A classic choice for formal gardens, boxwood offers dense, evergreen foliage that can be trimmed into precise shapes. Perfect for defining edges in plant boxes.

2. Lavender (Lavandula) – With its fragrant purple blooms and silvery-green foliage, lavender adds a touch of sophistication while attracting pollinators.

3. Japanese Holly (Ilex crenata) – This compact shrub mimics boxwood but is more resistant to pests, making it ideal for low-maintenance formal designs.

4. Dwarf English Laurel (Prunus laurocerasus 'Otto Luyken') – Glossy, dark green leaves and a tidy growth habit make this plant a refined addition to any plant box.

5. Rosemary (Rosmarinus officinalis) – Its upright growth and aromatic foliage provide both visual appeal and culinary utility, blending form and function.

For a cohesive look, pair these plants with symmetrical arrangements and geometric pruning. Opt for neutral-colored plant boxes to let the greenery stand out. With these selections, your formal garden will radiate timeless charm.