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.
This article is about Blackberries, but the information applies to Loganberries also.
There can be a few reasons for lack of fruit.
https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberries-not-fruiting.htm
Hi I have a very small allotment which I plan to grow a blackberry plant on (against the side of a shed). Could I plant a loganberry about 10/12 feet away?
Sure! They are closely related, and will grow just fine within the vicinity of each other.
Here is an article for their care:
https://www.gardeningknowhow.com/edible/fruits/loganberry/how-to-grow-loganberries.htm