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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.