A couple of years ago I started pruning after the first full moon in January. Before that I did it more or less randomly in January, when I could.
There was no real good reason for this. It was just traditional. People used to wait until after the first full moon in January to start pruning and they tried to finish by St Vincent's (The patron saint of winemakers and vinegrowers) day on January 22nd. Modern followers of the practice, including bio-dynamic farmers, believe that the moon's pull on the vines subsides after the full moon, and the plants will heal faster from the pruning and not loose as much 'energy' through sap bleeding.
I just figured "can't hurt".
I have seen better performance in my vines the last two years, but I've made so many other changes, who knows if the moon is having any effect at all. I remember Jerry Anderson telling me; "Farming is not science, it's trial and error, and you can never limit it to one variable". That's so true. I don't know what effect, if any, pruning on the moon phases has had, but I know it hasn't hurt, so I'll keep doing it.
We'll start on Saturday, and I'll work hard for the next couple of weekends to finish all the vineyards before St Vincent's Day. It also means 2007 is officially under way in the vineyard.