Arranging traditional plants in an outdoor plant box can transform your garden into a vibrant and harmonious space. Start by selecting a mix of plants with varying heights, textures, and colors to create visual interest. Place taller plants like lavender or rosemary at the back, medium-sized plants such as geraniums or marigolds in the middle, and trailing plants like ivy or creeping thyme at the front for a cascading effect. Ensure proper spacing to allow for growth and airflow, and consider the sunlight and water needs of each plant to maintain their health. Finally, add a layer of mulch to retain moisture and enhance the aesthetic appeal. With these tips, your outdoor plant box will thrive and become a focal point of your garden.