Creating a black hole fireworks-themed outdoor plant box is a unique way to bring cosmic wonder to your garden. To achieve this mesmerizing effect, focus on plants with dark foliage and flowers that mimic the glow of distant stars. Here are the best plants to consider:

1. Black Mondo Grass (Ophiopogon planiscapus 'Nigrescens') – Its deep black leaves create a dramatic, almost otherworldly backdrop.

2. Black Petunias (Petunia 'Black Velvet') – These velvety dark blooms add a touch of mystery and contrast.

3. Glow-in-the-Dark Flowers (e.g., Moonflowers or Night Phlox) – These blooms open at dusk, emitting a soft glow reminiscent of fireworks.

4. Dark Leaf Coleus (Coleus 'Black Prince') – With its rich, dark foliage, it enhances the cosmic theme.

5. Silver Dust (Dusty Miller) – Its silvery leaves mimic the sparkle of stars against the dark "void."

Pair these plants with subtle LED garden lights to enhance the glowing effect. This combination will transform your outdoor plant box into a captivating black hole fireworks display, blending nature and fantasy seamlessly.