If you want to improve the yield of your black raspberry plants, then there's 3 simple things you can do to ensure you get more berries.
- Head out to the garden in early spring (before the leaf buds break open) and pull your raspberry canes up to see how tall they are. Cut the tops off so that the plants are about 3 feet high. If you are between 5'2" and 5'4" that's about chest high. This will encourage lateral growth and more berries. If your laterals (side shoots, horizontal growing branches) get longer than 2 feet, trim them back.)
- Fertilize them with a good quality fish emulsion or product formulated for tomatoes (to encourage more flowers: more flowers equal more berries) in the spring once the leaves start popping out.
- Cut out and remove the old canes at the end of summer. This keeps everything clean and air circulating; preventing disease.
Then stick around in mid summer (around the 4th of July for zone 4) and enjoy all your tasty berries.