According to Everyman's right you can pick berries from nature when you don't disturp nature and other people with it.
Berries that you can find from Vuokatti:
Cloudberry, picking in the end of July and in August, grows on swamps.
Rasberry, picking in August , grows in places where forest is cut of about 5-10 years ago.
Blueberry, picking from July to October, grows in dry forests.
Lingonberry, picking in September, grows in boreal forest and artic tundra.
If want to know better our nature check this book!
I have lived here almost all my life and still this book presents new places to explore.