Creating a microscopic world-themed outdoor plant box is a delightful way to bring a touch of magic and whimsy to your garden. This unique concept focuses on tiny, intricate plants that mimic a miniature landscape, perfect for sparking imagination. Here are some of the best plants to include:

1. Baby Tears (Soleirolia soleirolii): These tiny, lush green leaves form a dense carpet, resembling a miniature forest floor.

2. Miniature Moss (Selaginella): Ideal for creating a velvety, mossy effect, adding depth and texture to your tiny world.

3. Dwarf Mondo Grass (Ophiopogon japonicus 'Nana'): Its small, grass-like blades are perfect for mimicking tiny meadows or pathways.

4. Fittonia (Nerve Plant): With its striking vein patterns, this plant adds a pop of color and intricate detail.

5. Creeping Thyme (Thymus serpyllum): A fragrant ground cover that blooms with tiny flowers, perfect for a fairy-tale vibe.

Pair these plants with small decorative elements like pebbles, mini figurines, or tiny fences to enhance the microscopic world theme. Ensure proper drainage and partial shade to keep your miniature garden thriving. With careful selection and arrangement, your outdoor plant box will become a captivating tiny universe.