It's quite normal that the canes on your Boysen plants are smaller diameter than Doyle and Triple Crown. Triple Crown (and maybe Doyle, but I'm not sure as I've never seen it being grown) is a semi-erect blackberry, and all of these varieties have quite thick canes.

Boysen and Thornless Boysen are trailing varieties, which are known for their thin canes. Thornless Boysen is actually just a bud sport of regular Boysen, so I can't imagine there would be a difference in cane diameter. Most trailing blackberries are grown for the processing market, so it's actually beneficial that they have thin, fairly flexible canes, which aren't damaged by machine harvesters.

Due to the differences in cane habit, most large commercial growers use a different kind of trellis for the different types of blackberries (erect, semi-erect, and trailing). This allows for better growth (or simply allows for machine harvesting).

Were you concerned about the health of your Boysen plants, or just curious as to why there's a difference in cane diameter between it and Doyle and Triple Crown?

Thanks for the feedback! I was mostly concerned about the diameter as the canes themselves range between 15-20 feet and average about 5-7 canes per crown. A (20 acre) berry farmer from Oregon told me they don't keep any canes smaller than a pencil since the size of the cane reflects the amount of stored energy and anything smaller than a pencil has proved worthless to them. However, they grow Marion and Chester, so that could explain their statement. Here in Alabama there are only two other full-time berry farmers in the whole state and for the most part they only grow erect thorny varieties. However, I've had quite a few compliments on my (testbed) boysenberries, so I just wanted to make sure I was growing the best variety as I plan to expand to 100 or so plants next year (2009) if all goes well. As you seem to know your Boysens quite well, do you have any thoughts on fertilization? They're going into their third year and I give them about 1 1/2 inches of water a week during the growing season and feed each plant about a cup of 13-13-13 at budbreak and then again after harvest around mid June and they seem to do OK. However, "they" say berry plants are heavy feeders so I just wanted to make sure I was in the ball park. Thanks again!

For fertility, there's a great reference from Oregon State. Google "caneberry nutrient management guide" and it should be the first thing that pops up. It's a PDF file. I have no idea how much fertilizer you should be applying per plant (I think in acres, not plants!), but you should definitely have foliar tests done. That's the only true way to know if your plants are getting the nutrients they need. A soil test might not be a bad idea either if you haven't already gotten one done.

As to water, you should be ok with the 1.5 inches per week, but you might want to use the "shovel method" (dig a bit a check for adequate moisture) during the hottest periods to make sure.

Marion tends to have similar canes to Boysen, so yours might be a bit on the thin side. Do you feel comfortable with your pruning and training? I'll post one link (to an Oregon State page) at the end of this message, and if you google search "growing blackberries in North Carolina" it will take you to another great document (PDF file).

As a final word on planting more Boysen, it does *not* hold well at all as it has incredibly soft fruit. If you do any pre-picked sales, you'll need to sell everything you pick the same day. I'd also advise u-pick customers to use or freeze any berries they pick the same day, or they'll end up with a mushy mess.

If you want a trailing type blackberry (so flavor will be much more similar to Marion and Boysen than Chester) that holds relatively well (yet still not as well as the erect types from Arkansas), try Obsidian, Metolius, and Black Diamond. Black Diamond is thornless, and Obsidian and Metolius are thorny.

Here is a link that might be useful: blackberries in Oregon

I have thornless boysenberries, and they are big and husky. I just ordered some more, and they're the thorny kind. I'm going to return them if i can and find the thornless ones. I didn't know there were two kinds.