Marion Berry Cultivation
I have done my total pruning of the old canes last fall after fruiting, but then the new canes grew out almost 20 feet with many many side sprouts, some up to 6 feet long. Should I leave it all on, or cut off the side sprouts? I can also cut out some of the entire new canes... there is just too much in the space I have. What would be better, take out some entire canes, or remove the side sprouts?
Outside United States marionberries
Sounds like you have a very happy berry patch! Marionberries are very vigorous, so it is fine to trim them to help keep them manageable. If they get too rambunctious it can be difficult to keep good air circulation and light penetration, leading to potential fungal and other infections. So you can certainly take out full canes... the rule of thumb is that a medium sized dog should be able to run through the patch... meaning there should be some spaces between the canes. And you can also trim back the remaining canes to whatever is manageable given your trellis system... 10'? 6'? It's best to leave the side branching however on the remaining canes as they are what produce the most fruit.