While kayaking several years ago, I found red raspberry plants growing wild on the rock cliffs along the river. They were in the most marginal growing conditions, with their roots growing into shallow dirt in cracks and grooves in the rock face. They were partly shaded by the trees and shrubs around them. In spite of all this, they had an abundance of juicy red berries.
I brought some home to plant in their own garden, giving them compost and keeping the pH to the proper level. The garden has trees on the east side so the light is partly shaded in the morning but full in the afternoon. Having given them all the advantages, I figured they'd take over the propery and produce berries the size of basketballs. I cover them with bird netting when the berries start to form otherwise the birds would eat them all.
After all this, they never produced as many berries as the wild bushes seem to do. They did produce a few new plants by growning roots at the end of the canes. I let those grow on their own for a year, then cut the cane to separate the plants.
Anything else I can do that might help produce more berries and more plants? I'm in northern Maryland, fairly close to the Chesapeake Bay.