I have 6/7 loganberries planted on a 4ft sunny wall and growing very well for about 3 years. They produce an abundance of small white flowers but not one fruit since planted. I have no problem with raspberries. Thank you.
Certified GKH Gardening Expert
This article is about Blackberries, but the information applies to Loganberries also.
There can be a few reasons for lack of fruit.