Temperate fruit trees are complex plants. A few examples of their complexity are:

• long lived and growth in current year is affected by growth in previous years.

• grafted, a combination of two genomes, one cultivar is a rootstock and another is the scion/productive cultivar.

• fruiting. Most initiate, differentiate and develop blossoms during the summer and bloom the next spring. Pollination and fruit set is a complex process and dependent on insect pollinators.

• They require direct sunlight on all parts of the trees for maximum fruit production.

Espalier training of these trees adds another layer of complexity.

Knowledge of the science of fruit tree growth and response to training is important to ensure well trained attractive trees and consistent cropping.