Training is to cause the branches to grow in a particular direction or fashion. The primary object of training and pruning fruit trees is to manage light. Shading of one leaf by another reduces light interception of the shaded leaf by 90% and thus reduces photosynthesis by 28%. About 30% of full sunlight is required to achieve the maximum rate of photosynthesis. In gardens, a secondary reason to train and prune trees is to improve aesthetics.
Limb orientation is an important factor in productivity. Branches that are growing mostly upward are vegetatively vigorous, but not fruitful. Branches that are growing mostly horizontal are very fruitful, but have too little vegetative vigor. The ideal branch angle is about 30° to 45° above horizontal. This allows for vegetative growth while providing as much fruitfulness as possible. It creates a balance between growth and fruiting. Careful bending of young branches, and holding these branches horizontally with string or weights, will help bring young trees into production.
Many different approaches have been used to train or position limbs. Spreading involves using wooden sticks or metal rods to push branches downward. Tying involves using string or twine to pull branches downward. The twine can be connected to a stout stake or to a nail or screw in the base of the tree stake. Weighting involves fastening small weights on branches to pull them downward. Filling small paper cups with concrete makes a simple weight. Put a J-shaped piece of wire in the cup while the cement is wet to form a hook for hanging the weight in the tree. Trellising can also be used for limb positioning. Many different types of trellises can be used for fruit trees. Some are very elaborate such as espalier. Others simply consist of two to three horizontal wires connected to strong posts. Limbs are attached to the wires to hold them in the desired position. Trellises can also help support a growing crop. Trellis systems don’t work very well for stone fruits.