Trees and shrubs can be formed into specific shapes. We treat these shaped plants as their own growth type, even if it is an artificial one that would not occur this way in nature. 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 do 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 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 dominant axes should be spaced 20 to 50cm apart, depending on the plant species and its needs. A spacing of 1 to 2m between the slats is sufficient if the trellis (lattice form) includes horizontal axes.
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).You will find information on the appropriate construction styles for each individual plant in the respective pages dedicated to the climbing plants.
Wire rope trellises which have meshes that are too close or too far apart, or are too tall or too low for the plant are not ideal and only suitable in certain conditions.
"Unsuitable" wire rope systems 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).