A number of high-rise dwellers create fabulous small gardens on their balconies. Being able to look out onto greenery from a 20th-floor apartment must be a real bonus when you are so far from the ground. Exposure to both sun and wind are extreme at these heights and high-rise gardeners have to employ all the tactics used by owners of larger plots at ground level, but squeezed into a narrow space. They have to anchor everything securely against the wind, for the safety of people below as well as their own plants. The weight-bearing capacity of the balcony is also extremely important.
Most start by creating a windbreak for their smaller plants by erecting a trellis along part of the balcony (not all, or the views will be obscured), Growing in pots and secured to the trellis are a line of wind-resistant trees and shrubs such as rowan (Sorbus aucuparia) (4-7), honey locust (Gleditsia triacanthos) (3-7), birches, cotoneaster, and evergreen Elaeagnus x ebbingei (7-9). With pruning and root restriction, they will not reach their usual heights and spreads. Within this windbreak, all kinds of smaller plants will grow, with places for shade-lovers and sun-lovers, including pelargoniums and even tomato plants. I have even seen lawn grasses grown in seed trays clipped with scissors and miniature ponds created in waterproof pots and containers. Small trees, shrubs, and herbaceous perennials can stay in the same, lightweight pot for many years as long as they are watered regularly and fed adequately. I’d opt for a slow-release fertilizer added to the top of the pot every spring. Top-dress with fresh compost when space in the top of the pot allows.