If you want to grow an espalier fruit tree not for the fresh fruit but as ornament, you should chose a quince. They are undemanding, vigorous, low-maintenance, and thrive in partial shade -- a very interesting alternative to apples, pears, or other fruits. The fruit of the quince can not be eaten fresh, but they can definitely be used for jelly and marmalade!
(lat.: Cydonia oblonga)
Quinces are undemanding fruit trees, but they need a permeable soil that is not too heavy. They thrive in sunny locations, but walls in partial shade are sufficient when they are grown as ornamental plants. Quinces can be found in local tree nurseries or ordered online.
When cultivated on an espalier, quinces are treated as shaped trees. They can grow to height of about 6 metres, with white large flowers in May / June. The fruits are strongly scented. The fruit become edible, if at all, when exposed to a lot of sun on southern walls-- in late October or November. Even when the maturity is not optimal, the fruits can still be used for jelly, marmalade, "quince bread," fruit juice, etc.. The pelt must be removed before processing. There are "apple" quinces and "peach" quinces, depending on the shape of the fruit. One pruning to thin out the branches per year is enough.
The table at the bottom of this page indicates which trellis designs should be used for a quince espalier. Choose a trellis in the heavy or massive wire rope ranges; for smaller espaliers you can also use a medium or basic trellis. Espalier trees can also be grown on wooden trellises. The climbing aid needs to be strong enough for the tree once it has grown to size. The main axes of the trellis should be about 60 cm apart. Any distance to the wall can be chosen. More details under "shaped trees."