The grapevines are still quite young, having had my first crop of grapes last summer. So this is the first time really "pruning" them. In previous years, it was more of selecting the shoots which I would train on the trellis. I have read lots of different descriptions on how to do it, and have been adequately confused by the terms and which of the Kniffen systems to use, and about the old wood vs. new wood, and how many buds to leave, to use as next year's lateral branches, or whatever. But I think the basic concepts which I understand are these:
1) Trim back quite a bit, since grapevines grow like crazy. I think I read somewhere that one should remove some 60% to 80% of the wood. Well, since mine are quite young, I was aiming for more like 25% to 50%.
2) Train the trunks vertically, the main branches horizontally, and then the offshoots (vertical, for the most part) from these are the ones which will bear the fruit.
One of the descriptions mentioned tagging (they tied a bright cloth onto) the branches which you want to keep, and then cutting away the others. So being the geek that I am, I decided that it would be even better to use one of the kids' paint sets (you know the ones, the sets of one-time use primary colours which seem to come with all sorts of art kits) to mark the branches.
I was very pleased by my painting technique. I have 3 main vines, so I decided to mark each vine with a different colour, to figure out what tangled branches belonged to each one. Here is the vines with the paint markings, before pruning (click any photo for a slightly closer view):
After painting the branches I wanted to keep, it was easy to prune out the others, since I could quickly trace them back to which vine they belonged to. If they came off the red one, they were chopped. If they came off the yellow or blue one, I evaluated more carefully whether I could also keep and train them onto the trellis. So in that way, my pruning should even the score somewhat, and hopefully give the other two grapes a chance to bear more fruit this year.
I am very pleased by the result so far. I could tweak a bit more, but the job is for the most part done: