Trees and shrubs can be trained to specific shapes. We treat these trained plants as their own growth type, even if it is an artificial one. Espaliered trees are brought from a "3D" to a "2D" shape by pruning and tying them in specific ways. Almost all perennial and woody climbing plants ("climbing shrubs"), as well as all fruit trees, can be trained to specific geometric forms on the trellis framework. The tying and pruning techniques are different for every species.
Fruit trees are especially compatible with façade greening, as they will benefit from the facade microclimate and bear sweeter and earlier fruits that they would otherwise. Grapevines also have a tradition in Europe as espaliered and formed plants, as well as firethorn, winter creeper, and cotoneaster. In facade greening, these are all treated as 'shaped trees.'
The trellis frameworks for an espaliered tree (made of wire rope, metal rods, or wooden lattices) are usually constructed in such a way that the shaping/formation of the plant takes place along the lines of the trellis, but the supporting trellis elements can also be placed diagonally or horizontally in relation to the trunk and branches. Selected young shoots are then fixed to the outside of the climbing aid with binding material or sometimes also put behind the ropes / rods.
Suitable trellises can consist either of only vertical lines, only horizontal lines, or can have a grid shape with one 'dominating' direction (meaning that in one direction the lattices will be further apart than in the other direction, as in a classic lattice fence where the vertical laths are close and the horizontal laths far apart). The spacing of the dominant axis should be between 20 and 50 cm, depending on the plant species. If there are still crossing/transverse axes (with lattice forms), an axis distance of approx. 1-2 m is sufficient.
The growing trunk and branches will apply a strong lateral pressure on the trellis, along with the weight of leaves and fruit. This is relevant especially for wire rope trellises and they must be designed and planned accordingly. Especially with trees that are not planted in their final shape but are trained on the facade, it is important that the main branches and trunk align with the anchor points (and not between two brackets) of the trellis, so that weight and pressure are optimally distributed.
The wire rope systems with square grids should be modified so that one axis is more dominant (see above).
Wire rope trellises which have meshes that are too close or too far apart, or are too tall or too low for the tree, are of 'limited' suitability.
Rope systems which are "unsuitable" are those which do not correspond to the growth behavior of the selected plant-- i.e., those which are too small (short), too tall, or too narrow. It is also possible that rope systems are not related to a planned plant formation, e.g., a system with only one axis (one rope line) shouldn't be used for an espalier tree. Some rope systems have a grid that is too narrow and too expensive for its intended purpose (5050).