Fruit bushes - stake or not?

Our Blueberries planted in ericaceous compost are pathetic, the other one we just planted in "dirt" way out performs the others, ????????

 

I forgot to mention, my soil does not drain, being solid clay dug from the pond - that was also a huge problem the raised boxes solved, that and being able to be watered properly. ph is the key if drainage is not a problem. People I know, and trade eggs with, have rows of blueberries 7 foot tall and drooping with blueberries that were just stuck into a hole in the ground a few years earlier - different soil completely once you get inland and away from the coast. That is what my goal is for my plants, but in boxes.

 

am I correct in thinking Rhododendrons need acidic soil ? if so I think were acid the local woods are full of them - but I best get a kit and check