Prune raspberries in winter to increase your harvest and reduce pest problems.
Summer and everbearing raspberries form fruit on 2-year-old canes. Start by removing any canes that bore fruit last summer. These are done producing and when left in place increase pest problems and make harvesting more difficult. Prune these 2-year-old canes to ground level. Leave stems intact on everbearing plants that bore fruit in fall. These one-year-old stems will produce berries this coming summer.
Now thin the plantings to 3 to 4 canes per foot or 6 to 8 stems per hill. This will open up the planting for better light penetration and air circulation. This means fewer disease problems and a bigger harvest.
Remove no more than ¼ the total height of the remaining stems. The more you prune the smaller your harvest.
Fall raspberries can be cut to the ground. Pruning back all the stems eliminates the summer crop, but results in an earlier and larger fall harvest.
A bit more information: Routine pruning is also a great time to manage insect and disease problems that are present. Start the pruning process by removing any discolored, swollen or damaged stems. Destroy these potentially infested stems to reduce future pest problems.