Too early in the season for pruning new growth on caneberries; there are many recommendations to prune the main cane at waist to shoulder high if you want branching (all the branches will eventually reach down to the ground also).

A trellis is often used for these; it's main purpose is to keep the plants upright for training and ease of harvest.

Most caneberry varieties, if allowed to arch over to the ground, will take root there. That is how wild berry thickets form.

The term you are looking for is tipping not pruning, the idea is to force branching by removing just the tip, not to remove structure. The height at which you should tip depends on the variety of thornless blackberry, as some are more self supporting than others, though most (all) benefit from a trellis to support their weight when loaded down with fruit. Generally though they should be tipped at height of between 3 to 4.5 feet, and the erect growing varieties will become more and more erect each year for the next 2 or 3 years, with the stalks getting thicker each year.

p.s. most experts say it is better to soft tip, by sharply bending over the last inch or so of growth than it is to hard tip by cutting as it lowers the chance of infection.

thanks all, I soft tipped the long shoots and they are growing new branches already in just a few days.

splats, do you know what variety you planted? Can you post any photos of the plants? It sounds like you're talking about all new canes for this year. I grow Apache and it's recommended that you only leave 3 new canes per bush and to cut to a height around 42". If yours will grow like mine, you should trust them on this. lol!

Here's a guide for growing thornless blackberries.