[AlittleSalt]

What many here have told me is that, yes you can use the same container mix. I have some fall tomato plants growing in containers that I used earlier this year. I use the Master Blend, Calcium Nitrate, and Epsom salt mix in one container. The other two containers - I've just been watering with no other help. The Master Blend, Calcium Nitrate, and Epsom salt mix plant is 4 times larger than the others. So my answer comes from seeing results, and it is that, "Yes, you can reuse that mix."

The rest of your question - I am also wondering about using organic additives in the winter/off season for next year's crop. I wish I could give you an answer, but I'm learning along the way too.

I left out that all three containers are growing Japanese Pink Cherry tomato plants.