Most gardeners prune the main canes at 4 to 6 feet, depending on their trellis. You do not have to leave them alone.

Trimming 3 feet off of 12-foot-tall canes would still leave an inconvenient height, unless you meant the canes are 12 feet long, at an angle, and not that high above the ground.

Triple crown canes, for ex ample, can certainly go straight up 12 feet, some would arch over before then.

Canes that are pruned now still have plenty of growing season to form more easily reached and netted laterals.

larrry gene, thanks for your reply. The blackberry bushes I have are Ouachita, thornless and extremely vertical. This years new canes are already 12 feet tall. I'd love to take them down to about four and a half feet tall, if that is ok. I don't want to ruin their energy for growing laterals and fruit next year. Thanks again, Mrs. G

I'm not very current with blackberries as I don't manage many but I always cut the primo-canes back during the growing season a couple of times to encourage laterals. The fruit all comes from wood formed the previous season except with Jewel and Jim (or is it Jules).

I would cut them back and risk it. I have the same variety as you and each year have thought about tearing them out and putting in another peach tree.

I pay careful attention to what Olpea says. So this year gave them a new lease on life with a completely open mind.

He does not let them get above 4' tall and I have adopted that for this year.... My canes from last year died so I am starting new with lots of strong canes without the interference of the 2nd year canes. He starts pinching off tops when they are 18". As for maintaining 4' he said something like, when they are above 4' and you have the time, cut them back to less then 4'. this keep the large canes from tearing themselves out of the ground and keeps the bushes nettable. And in my case living in town, they aren't so gangly and ugly looking in the yard.

Thanks to all of you! Out come the clippers today. Netting can now go on as the berries are getting very large. Thanks again! Mrs. G

A better time to do this is when the main cane is around 5 or 6 feet tall, that leaves even more time for lateral growth. Next year start earlier.

I just took three 7-foot triple crowns down to 5 feet today.

I think Prime Jan and Prime Jim are the primocane fruiting blackberries you were thinking of Harvestman. Prime Ark 45 is a 3rd. I've got Prime Jan and while the fruit is only OK, the nice benefit is that you get berries much later in the season, after all the normal blackberries are done. But, with SWD, I got almost no usable berries last year, as it hit half way through the normal blackberry season.

Mrs G, I agree with Larry- when the cane is 5-6 feet tall, I go around and pinch off the top 3" of the cane with my fingers. No need to chop much, just enough to direct the growth outwards. Since I don't need clippers, it is a nice activity for when I just happen to be passing through.