How do I get my Blackberry plants to produce large fruit

Question

Plants only produce small size fruit. How do I get my Blackberry plants to produce large fruit?

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Answer 1

I would review this article on the care of blackberries, as following these guidelines will help produce better berries:
https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm

Furthermore, this article (PDF) from Cornell University discusses pruning techniques that may encourage larger berries:
https://bit.ly/1LDlF7G