My established boysenberry plant is developing long stems with thorns. The estiablished stems do not have thorns. What can I do for them?
Thorns are normal unless you bought a thornless variety, and even then, thorns can return. Here is how to prune your boysenberry canes:
https://www.gardeningknowhow.com/edible/fruits/boysenberries/effective-boysenberry-pruning.htm