This spring, because of Covid, I didn't feel like going to the store to buy Promix. I had kept my pots, still full of Promix in the shed over the winter as I had read that people re-use their mix and add some nutrients. Thank goodness I had done that! I emptied them (individually) into a wheelbarrow so that I could add 1/4 of my own composted chicken manure to each pot.
I'm happy to say that all my compact tomatoes grew very well in last year's Pro-mix with added composted chicken manure
. I would venture to say that they grew as well as they had the previous year when I grew them in new Pro-mix.
Linda