New American Dream Dictionary

by Joan Seaman - Tom Philbin
1. Unconscious sexual desires emerge.

2. A need to use more vigilance in affairs, business or emotional.

3. Possible re­versal of fortune.

The Complete Guide to Interpreting Your Dreams

by Stearn Robinson - Tom Corbett
Whether you saw them, picked them, or ate them, blackberries predict reverses.

Pull in your belt and be prepared to struggle for a while.

Dream Symbols and Analysis

by DreamForth
A dream in which you see or eat blackberries means that you are acting without caution.

It is also symbolic of repressed carnal urges.