I purchase 8 thornless blackberry bushes from the local Pa. (Wayne County) Conservation Dept. about 8 years ago. They look vigorous and in good, loamy soil and have good drainage with full sun. They have never produced more than a handful of berries. I prune them back in the spring and they grow back vigorously, but again no berries. Do I need another variety?. Should I dig them up and start from scratch? They don't look diseased, but they don't produce. Suggestions? Thank you.
I'm in the UK, so not sure if what we call blackberries are the same as what you call blackberries. Anyway, are you sure you're pruning them properly? For my blackberries, every winter I cut to ground level all the canes that have fruited. The new canes that grow out of the ground this year will fruit next year. So these canes will be cut to the ground at the end of next year. If I cut everything back in the spring, I'd be cutting back the fruiting canes and wouldn't have any fruit. For more detail see https://www.rhs.org.uk/advice/grow-your-own/fruit/blackberries