Circumnutation, the graceful, spiraling movement of plants as they grow, is a fascinating natural phenomenon. To observe this behavior in outdoor plant boxes, certain species stand out due to their pronounced and visible movements.

1. Climbing Plants: Species like beans (*Phaseolus vulgaris*) and peas (*Pisum sativum*) exhibit strong circumnutation as they search for support. Their tendrils twist and turn, making them ideal for demonstration.

2. Morning Glory (*Ipomoea purpurea*): This fast-growing vine shows dramatic circling motions as it climbs, perfect for small outdoor plant boxes.

3. Hop Plants (*Humulus lupulus*): Known for their vigorous growth, hops display clear circumnutation, with stems spiraling as they reach upward.

4. Passionflower (*Passiflora spp.*): With its rapid growth and twining habit, passionflower vividly demonstrates circumnutation.

5. Sweet Pea (*Lathyrus odoratus*): A favorite for gardeners, sweet peas exhibit elegant spiraling movements as they climb.

For best results, provide trellises or supports in your plant boxes to encourage these plants to showcase their natural movements. Regular watering and sunlight will further enhance their growth and circumnutation display. Observing these plants can be a delightful way to study plant behavior in small outdoor spaces.