Nutational tropism, the helical movement of plant stems as they grow, is a fascinating phenomenon best observed in climbing and twining plants. For outdoor plant boxes, selecting species that exhibit pronounced nutational movements can create a dynamic and visually engaging display.

1. Morning Glory (Ipomoea purpurea): This fast-growing vine showcases elegant spiraling tendrils, making it ideal for observing nutational tropism. Its rapid growth allows for daily visible movement.

2. Sweet Pea (Lathyrus odoratus): Known for its delicate stems that perform conspicuous circling motions as they search for support, sweet peas are perfect for small plant boxes.

3. Hop Vine (Humulus lupulus): A vigorous climber, its bines twist clockwise with a distinctive helical growth pattern, demonstrating nutation clearly.

4. Runner Beans (Phaseolus coccineus): These twining plants exhibit strong nutational movements, with stems that rotate noticeably as they reach for sunlight.

5. Passionflower (Passiflora spp.): With their grasping tendrils and spiraling growth, passionflowers beautifully illustrate nutational tropism while adding exotic flair.

For optimal observation, place plant boxes in sunny locations and provide trellises or supports. Regular watering and balanced fertilization will enhance growth movements. By selecting these species, gardeners can create a living demonstration of plant biomechanics while adding vertical interest to outdoor spaces.

Note that nutational movements are most pronounced in young, rapidly growing stems and are influenced by light (phototropism) and gravity (gravitropism). Observing these plants at different times of day can reveal how environmental factors affect their growth patterns.