February and March is the best time to prune most trees and shrubs in Iowa. The absence of foliage at this time of year gives you a clear view of the tree and allows the selection and removal of appropriate branches. Also, when pruned in the late dormant season the walling-off, compartmentalization, or sealing of wounds can begin as soon as growth starts in the spring giving the tree the most time to recover from the pruning cut.
Iowa State University has many resources available to help with pruning all your woody plants.
Raspberries in the Home Garden