From the Archives of American Gardens (AAG) 
Written by Julie Hunter, AAG/GCA Garden History & Design Intern August 2012
Submitted by Lindsay Dodge 

Espaliers are designed to accent a garden, providing an intricate visual attraction.  Trees or shrubs are trained on a wall or on a trellis to form different, oftentimes decorative, patterns. Of interest, they serve a functional purpose as well. 

In the 17th and 18th centuries fruit trees were often trained against kitchen walls. Not only did the trees provide an ornamental aspect to the garden but being planted and trained against a warm and sunny spot like a south-facing wall aided in fruit production. The fruit was of a better quality and grew faster because of the warm and sheltered environment. Placing fruit trees along a wall also enabled fruit to grow in a compact space while providing shelter to vegetables growing below. 

The Oxford English Dictionary defines espalier as: 1) a lattice-work or frame-work upon which fruit trees or ornamental shrubs are trained and, 2) a fruit tree trained on a lattice, usually of woodwork, or on stakes. While espalier refers to the framework that supports the plant, the term also implies the whole process, the framework, the plant, and the act of training the plant. 

Although it is not used as much, the term espalier can also refer to plants trained to create borders. Plants are trained in such a way that they establish a dividing line or defining edge for a garden, much like pleaching but without the extensive work of cutting and grafting the plants.