Although apple trees are very beautiful, they actually belong in the open 'field' (free-standing) and not really on walls... Wire trellises like the 0050 may be used to build free-standing trellises for one or more apple trees. Most apple varieties are already demanding enough to cultivate 'in the open' and won't really benefit from a wall microclimate. Instead of using the extra heat to mature fast, they tend to lose their aroma and tanginess (acidity) and become susceptible to diseases or pests. If there is no other space in the garden, it is then worth it to try growing them as espaliers on the facade.
(lat.: Malus domestica)
Apples should be grown on west facing walls, because apples may "boil" if the temperature is too high. The soil should be deep, humus-rich, and damp with a good water supply. The weaker the grafted rootstock, the less the tree should share the soil with other plants, bushes, and grasses. In extreme cases the ground needs to be mulched. Apple trees are available in tree nurseries or online.
To insure fertilisation, two matching apple varieties must always be present near each other-- either as two individual plants or as one espalier apple with double grafting. There are special varieties for espalier, the fruits of which are in high demand as rarities, such as "White Winter Calvill." Many of the old varieties are, however, susceptible to mildew and therefore not so suitable as wall espaliers. New, multi-resistant varieties are often better suited.
Apple trees are always grafted... for small or low trellises (height x width: 3 m x 2 m) mostly on the slowly growing rootstock "M9." Such graftings are then sold as "low trunk," "quarter standard," "bush," or "tall spindles." There are also expensive trees available that are pre-trained as espaliers. The lifespan of an espalier is only 20 years. For medium-sized espaliers (height x width: 4 m x 3 m), apples on the stronger base "M 26" should be used; these trees are sold as "half standard." Larger trellises (height x width: 6 m x 3 m) require medium-strong rootstocks- such as "M 4," "M 7," or "MM 106," which can last for 30-50 years.
Columnar apple tree and dwarf fruit trees aren't suitable as facade espalier trees.
Below is a table of all suitable shapes for wire rope trellises. For an optimal distance between the tree and the facade, choose a trellis in the heavy or massive range; a system in the medium or easy range also works. Apple espalier trees can be grown on a wooden trellis. In an open field / free-standing situation, use a 0050 trellis.
The trees are trained to their final shape through pruning, bending, and binding. Apple espaliers are usually grown as "tall spindles" (see photos below). Older names for this shape are "vertical cordon" or "vertical cord tree." The fruit-bearing wood branches off directly from the middle trunk and the shoots are tied horizontally 60 cm above the ground in levels of every 40 cm or so. When apple trees are planted next to each other they build long hedges. Other shapes, such as the Palmette Verrier, are used for larger trellises. Technical literature on pruning is available online. Without a correct pruning technique, the trees will bear fewer fruits or may not bear any fruit at all! The design of the trellis and the shape of the tree need to fit each other. As described in the section on shaped trees, the main axes of the trellis should be 35 - 40 cm apart.