Yes. An urban planter box can absolutely be used to grow plants vertically when you add a trellis, and it is one of the most practical ways to make a small balcony, patio, rooftop, or courtyard more productive. The planter gives the plants a contained root zone, while the trellis add-on gives climbing stems something to grip and guides growth upward instead of outward. This can save floor space, create a living screen for privacy, soften hard urban surfaces, and make better use of available sunlight.
The key is to match the trellis and the plants to the planter. A lightweight trellis is fine for peas, pole beans, nasturtiums, morning glories, and small tomatoes, but heavier climbers such as cucumbers, squash, or clematis need a stronger frame and a larger soil volume. Attach the trellis securely to the planter or to a nearby wall, railing, or bracket, and check that the whole setup will not tip in wind. On balconies and rooftops, wind exposure can be much stronger than it seems at ground level, so stability matters as much as style.
Soil depth and watering are also important. Vertical plants still need enough root space, drainage, and consistent moisture. A shallow planter may dry out quickly once vines and foliage cover the trellis, especially in summer. Use a high-quality potting mix, add mulch to reduce evaporation, and consider drip irrigation or a self-watering insert if you are often away. Fertilize regularly because crowded roots and heavy top growth use nutrients quickly.
Choose compact or container-friendly varieties, and prune or train vines before they become tangled. Make sure the trellis does not block light from other plants or create a damp, airless pocket. With a sturdy planter, a well-anchored trellis, suitable climbing plants, and reliable watering, an urban planter box with a trellis add-on can work very well as a vertical garden.