Aloha Margaret,
Other than the classic "start with new soil," and if you've dowsed for negative vortexes, entities, etc. I'd send energy and prayers to that box, seeing it bathed in healing light and growing abundantly. If you have the Spring Forest Qigong course, you can scan for blockages, clear, and send energy to the plants and soil.
Of course, that may be a wonderful spot for an ornament/piece of art to bring beauty to the rest of the garden around it.
Much Love, Shawn