We love plants for who they are. We like to see them grow as they have evolved to do, and vertical gardens provide a perfect medium for many plants to do so. The epiphytes (those plants that grow upon trees and other plants) and hemi-epiphytes (those that start life on the ground and then grow up towards the canopy) in particular are very at home in this environment, provided a few basic needs are met.
Without reaching too far into the reasons why many vertical gardening systems are designed to be densely planted from the outset (it seems to have been a natural progression for the industry to provide an instantaneously lush and full garden instead of one which required time to reach its intended glory), we can easily see the effects on the plants themselves. Commonly used plants which typically climb in their natural habitat are perfect examples of this: how often do we see a pothos or Philodendron climbing up a wall instead of cascading down? The weeping effect that the latter creates is admittedly pleasing (though there are plants which naturally possess this type of growth), but I believe that to create a truly spectacular and natural effect the best thing is to allow the plant to grow naturally; that is, up. And to do this, the plant needs space.
Many vertical garden systems are composed of cells, many filled with growing media, and some merely holding potted plants. These systems are fantastic if frequent replacement of plants is necessary, but this type of growing environment does not emulate a natural one. Other systems employ an undivided planting area, where roots are free to grow where they will. In these systems, if a plant is provided sufficient space, it will begin to grow upward, affixing itself to the growing surface with its aerial roots, tendrils, suckers or rhizoids, depending on the species in question. Once growth begins in this fashion it progresses rapidly, and something even more fascinating begins to happen: the plants' new leaves begin to grow larger than the last! Simply as a result of being able to grow as it has evolved to do, the plant performs better and produces a nicer specimen than one constrained in a planter.
This effect becomes more dramatic still in the case of some hemi-/epiphytic species because they possess a juvenile and adult form. Monstera dubia is a splendid example: the juvenile form of the plant grows with its silver-brushed leaves tightly appressed to the growing surface, but when it reaches maturity it suddenly abandons this growth pattern to produce large green leaves which take full advantage of the higher light in the forest canopy. It uses this extra energy to finally, after its long climb, produce flowers and ultimately reproduce. Incredible!
Many designers of vertical gardening systems seem to have lost their way; in what other horticultural discipline has a garden ever been designed to be instantaneously lush and full (or crowded, for that matter)? Certainly not in most traditional landscaping, and not even in most interior landscaping situations. It is a pity that now many people showing an interest in these gardens are expecting such fullness at the outset, for it is truly at the expense of the true potential of the vertical garden and the species therein.