Creating a mystery garden in outdoor plant boxes is a delightful way to add intrigue and charm to your outdoor space. The key to a successful mystery garden lies in selecting plants that evoke curiosity, offer visual interest, and thrive in confined spaces. Here are some of the best plants to consider for your mystery garden:

1. Coleus (Solenostemon scutellarioides) – With its vibrant, patterned foliage, coleus adds a splash of color and mystery. Its leaves come in various shades, from deep purples to bright greens, making it a standout choice.

2. Lamb’s Ear (Stachys byzantina) – The soft, velvety leaves of lamb’s ear create a tactile element in your garden, inviting touch and adding a whimsical feel.

3. Black Mondo Grass (Ophiopogon planiscapus 'Nigrescens') – This striking plant features dark, almost black foliage, perfect for adding a gothic or mysterious vibe to your garden.

4. Moonflower (Ipomoea alba) – A night-blooming plant, moonflower opens its fragrant white blooms at dusk, adding an element of surprise and enchantment.

5. Japanese Painted Fern (Athyrium niponicum) – With its silvery-green fronds and purple stems, this fern adds elegance and a touch of the exotic to your plant boxes.

6. Heuchera (Coral Bells) – Known for its colorful foliage, heuchera comes in shades of purple, silver, and burgundy, making it a versatile and eye-catching choice.

7. Ornamental Grasses (e.g., Pennisetum setaceum 'Rubrum') – These grasses add movement and texture, creating a dynamic and mysterious atmosphere.

For a truly captivating mystery garden, mix these plants with varying heights, textures, and colors. Ensure your outdoor plant boxes have proper drainage and are placed in locations that match the light requirements of your chosen plants. With the right selection, your mystery garden will become a conversation piece and a source of endless fascination.