Once they've been trained, in principle there's not much difference between pruning espalier fruit trees and conventional fruit trees. Ours are about 30 years old and have already been well-trained, so they now simply need to be maintained. The trees are so long-established that they also no longer need to be attached to the trellis.
The first principle is maintaining the shape when seen from all sides. This means that when seen from the front, there shouldn't be more than 4 to 5 strong horizontal branches on each side of the trunk. In our case, the trees hadn't been pruned for a while and were already developing additional branches, often protruding to the front or back instead of to the side. They had to go. Click photos to enlarge.
Another thing that had to go were the long vertical shoots along the top of the espaliers that make them look like they have "hair". Here an example of an unpruned "hairy" tree.
Seen from the side, you want to maintain the "flatness" of the row of trees. Keeping this in mind also helps in deciding what to remove.
As with other fruit trees, it's important to thin out twigs that interfere with each other, and to make the cuts just above eyes or branches pointing in the direction that you want the tree to develop in.
Here there are too many twigs:
Here's what it should look like after clean-up:
Here are some examples of finished trees. You can get a feel for how much was cut off if you click to enlarge. I was a little dismayed, but now, a month later, the trees are about to burst into blossom and they look just great. I'll post some photos of when they're in full bloom.
