It’s late September and my raspberries are done producing fruit. The canes are really tall. How should I go about pruning them?
According to Linda Gilkeson’s Backyard Bounty: The Complete Guide to Year-Round Gardening in the Pacific Northwest (New Society Press, 2018), the simple method is to wait until the dormant season and cut down canes that bore fruit last year. (You can tell these canes by their rougher and darker grey bark, compared to the lighter and smoother canes of the last growing season.)
This will work for summer-bearing as well as everbearing varieties, but some choose to prune everbearing (also called primocane-fruiting) raspberries in two stages. An everbearing raspberry is one that produces fruit in the early fall of the first year on their primocanes. It then fruits a second time, in June, on buds below those which fruited the previous fall. In the dormant season, prune off only the top part of the canes that have fruited, and let the remainder fruit next summer. Then you can prune out the whole spent cane the next winter. Try to keep only five to ten new canes per plant.
This Oregon State University Extension guide to Growing Raspberries in Your Home Garden may also be helpful to you.