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We have had the bushes for about 5 years now, I think they were 2 years old when we bought them

So living in pots has not deprived them of anything as far as being fruit producers.
So you feed them in anyway?

You have to keep adding to the pots but it is as simple and cheap as piling on grass clippings. I do this several times through the season. I also add a cup of blood meal per pot in the early spring and again in the fall. Chicken manure is also very good and I do this when it is available. Through the winter, I toss my expended tea herbs in them too.

I know someone who is trying to grow things in pots. I will have to share your ideas with her.

We used to put blood meal on the blueberries (that are planted) but the dog always dug into them and made a terrible mess so we stopped using that one particular fertilizer. She died this winter so we will have to start using it again.
Thanks for the reminder.