Just what do fruit tree experts mean when they say, "You need train your fruit tree?" Home orchardists need to train their trees for structure to encourage fruit production, to have a high-yielding home orchard, and to have a tree that can hold the fruit load without needing to prop or tie up the branches. The scaffold branches are positioned to allow good sunlight throughout the canopy to promote fruit production from the interior to the outside of your tree's canopy. This also will allow air circulation in the canopy, reducing leaf and fruit diseases, so you benefit in two ways.
Using dwarf apple trees as an example, you will likely use what is termed the "central leader system" to train your trees. The central leader system allows your fruit tree to look much more like most other trees in your landscape, yet produce apples without the tree looking like those you see in older commercial orchards. Training starts the first year you plant the dwarf trees. This will ensure your dwarf tree actually remains dwarf in your home orchard. You will be able to start to select your scaffold branches placing the first set of scaffold branches no more than 20 to 24 inches from the ground. By starting that low, you will be able to place additional scaffolds and still have a mature tree that is no taller than 6 to 8 feet tall, making it very easy to manage. If a dwarf tree grows without being well trained, that fruit tree will be much larger that you planned for and fruit production will likely be delayed.
There are several other advantages of a well-trained dwarf fruit tree. At annual spring pruning, it will be visually much clearer to see which branches will need your attention. There will be branches that need to be adjusted using traditional branch spreaders or alternative methods, such as using twine and a stake to pull the branch into the desired horizontal plane you need as you develop your scaffolds. Water sprouts will be easily identified, as they will be growing straight up from the horizontal scaffold branches. These will be more prominent as the tree matures on the horizontal scaffolds.
As your dwarf fruit tree matures in size and fruit production, home orchardists will realize there are additional benefits. The weekly inspection and monitoring of fruit pests will be easier and done very quickly. Even though a young fruit tree may not be producing apples, there are insects and foliar diseases that need to be taken care of.
Foliage feeding insects reduce the canopy, which decreases the amount of food that could go into growth and development. Leaf diseases have a similar impact. If allowed to continue over the season or seasons, it could easily delay fruit production and in a bigger picture, lessen the overall vigor. You want a tree that develops quickly, so that your training can then encourage flowers and fruit set. Enjoy the challenge and amaze your friends with fruit that came right out of your yard.