A couple of weeks ago, I repotted a few junipers. All had major root reductions done to them. Since then the new growth has exploded. I was just wondering how long I should wait before I begin to pinch them back.
Not knowing what you're working with, if it helps, I repotted a shimpaku last spring at a Boon workshop. Lots of root work was done, as the tree had been growing in a nursery container for a while. Boon recommended not doing any work on the tree for a year (aside from minor trimming of weak foliage), and just let it recover and grow.
Boon also isn't a big fan of continually pinching junipers - by continually pinching off new growth, he believes you end up weakening the tree.
I'm also a bit surprised that you have explosive growth after repotting a couple of weeks ago. Junipers seem to be on the slower side when it comes to growth.
By cutting back. A healthy juniper should be sending out runners (longer shoots that move beyond the silhouette). We make the tree healthy and keep it compact by opening up the foliage, removing weak branchlets, etc, and letting the runners go. when they get long enough, cut them off and force the growth inward. Once the tree is "finished," you can pinch individual runners to keep it in shape, but never whole pads. This weakens the tree and makes it leggy and too thick at the extremes.
Chris is correct regarding junipers... Unfortunately, to truly learn to prune the species, it is best and sometimes necessary to have an actual teacher show you how to do it. Not just on 1 juniper either, on 10's/100's of them.. Junipers in different stages and of different species... When you read articles and books, although the articles can be very well phrased and knowledgeable, it takes learning in person to really understand it...
Many times it is all about planning your next steps. It is not about what you have now, but what you will have....
Rob, man that was a mouthfull Context, context, context. There are so many people that want to take one technique that they've read or heard about and apply it to any and all trees regardless of what stage of development. Growing bonsai takes long enough when you're doing it right and when technique is not used in context,you know the story