What is an Espalier? An espalier (pronounced “es-PAL-yer”)is a plant that has been trained to grow in a flat plane against a wall,fence, or trellis, though the term has also been used to describe the technique of training a plant to grow this way. The technique was invented by the ancient Romans, and further developed in Europe. This technique allowed them to take advantage of the thermal mass of south facing walls (full sun in Northern Hemisphere) by growing fruit trees aga