Ask Mr. Smarty Plants

Rubus idaeus (American red raspberry) and Rubus canadensis (smooth blackberry) produce biennially,  growing primocanes one year, which become the berry producing floricanes the next year. The floricanes die and need removing after they have fruited. The primocanes, which will bear fruit the following year, emerge from the base or roots of the old canes.

Though wild hedgerow blackberries are quite adapted to the locations they select to spread themselves, you undoubtedly have one of the many commercial cultivars. Such plants prefer an area with good ventilation, full sun, and well drained, rich loam with a pH between 5.5 and 7. You do not indicate that your plants appear diseased or infested. In that case, three possible problems come to mind. First, you may want to check the pH of the soil to make sure it is appropriate for these plants. Second, some blossoming and fruiting species may produce luxiurous green growth and no fruit when they have too much fertility, particularly nitrogen. If you are fertilizing your plants, a recommended blend is 10-10-10.  Finally, consider if the winter temperatures have been too cold for the plants. Perhaps some winter protection is in order. 

There are other resources that are appropriate for you to check out. Consider contacting the supplier of your blackberry plants who may be aware of specific requirements for the cultivar you purchased. A local source of information for you is your Sauk County Extension Office. The agents there are knowledgeable about local conditions. Finally, the Essential Gardening Guide site suggests a plethora of potential problems in raising blackberries. Good luck in resolving this problem with unproductive blackberries!

Rubus idaeus ssp. strigosus

Rubus canadensis