Equinoctial tropism, the phenomenon where plants adjust their growth in response to the sun's position during equinoxes, is a fascinating aspect of botany. For gardeners looking to showcase this behavior in outdoor plant boxes, selecting the right plants is key. Here are some of the best options:

1. Sunflowers (Helianthus annuus): Known for their dramatic sun-tracking movements, sunflowers are ideal for demonstrating equinoctial tropism. Their large heads follow the sun from east to west, making them a standout choice.

2. Morning Glories (Ipomoea purpurea): These vibrant climbers exhibit clear tropic responses, with their flowers opening in the morning and closing in the afternoon, aligning with sunlight patterns.

3. Bean Plants (Phaseolus vulgaris): Bean plants show noticeable leaf movements throughout the day, adjusting their orientation to maximize sunlight absorption.

4. Cotton Plants (Gossypium hirsutum): Cotton leaves exhibit heliotropism, moving to face the sun during the day, which makes them excellent for observing equinoctial tropism.

5. Tropaeolum (Nasturtium): These colorful flowers not only add beauty to plant boxes but also display subtle sun-tracking behaviors, making them a great addition.

To optimize growth, ensure your outdoor plant boxes receive ample sunlight and are positioned to allow unrestricted movement. Regular watering and well-draining soil will further enhance these plants' natural tropic responses. By choosing these species, you can create a dynamic and educational display of equinoctial tropism in your garden.