I planted 400 Columbia Star marionberries in 2016 (from plugs) and had a healthy crop this July. I've been growing traditional (thorns) marionberries for about 15 years at another location. These new berries act a bit differently. The old canes were cut to the ground in August and the new canes are on trellises and look great. But I see new canes emerging from the crown plus hundreds of branches off of the trellised canes. Should I cut off these side branches which are several feet long, or try to tie them on to the trellis and should I cut the emerging canes at the crown? I've never had this much growth and not sure what to do at this time of year. Thanks!
Multnomah County Oregon
Columbia Star is a new cultivar of trailing blackberry that is thornless. It is certainly different that the other commonly grown trailing blackberry Marion (also known as marionberry).
Columbia Star does have a very different growth habit than Marion. It is thornless, produces many more canes and the average cane length tends to be shorter.
I would suggest leaving the plants as they are at the moment (not pruning any more this year) and instead remove any canes that are too short to train up, or any branches that are too short or too low in late winter. This way there is no chance that you will affect the plant's normal growth cycle -- we need these plants to enter dormancy as soon as possible for maximum cold hardiness.