My Nana had "a green thumb". She had amazing plants growing in the windowsill of a high rise condo building in Chicago! Not strawberries, but huge aloe vera plants and herbs like basil and mint.
She swore by burying a banana peel in her potting soil. Have you ever heard of that?
Generally burying the banana peel is a quick shot of nutrients since the peel breaks down fairly rapidly and they are high in I think calcium and magnesium.
I guess they really work magic because with the climate and limited sunlight she was working with, it's amazing what she was able to grow!