Recycle living soil. Plant cover crop that survive freezing winter or wait until spring?

Hi, I have a couple of 20 gallon fabric pots that were used to grow a couple nice bushy girls outside this summer. They were grown using Living Organic Soil. Now, I would like to convert and prepare them without tilling so that they would be ready by next June. The plants I grew this summer were chopped about a month ago and I have not pulled out the root ball yet. I have to following questions.

1. How can I re-amend these pots without tilling? I suppose I can plant some cover crops and chop the cover crop/mulch them before planting in next June? But this would only take care of Nitrogen. How can one re-amend the soil with other nutrients? I suppose I can top dress these pots with my regular amendments? Then top dress with compost and ewc. Then a layer of cover crop seeds, and more compost on top so the cover crop would sprout? And I'm done?
2. These pots live outside in cold winter (49N, Vancouver BC). I read that hairy vetch can survive below freezing. Now, I don't need these pots until next June. So, if I sow some hairy vetch now, would they sprout as the weather is getting cold now, around 5C. If they do sprout, I suppose they would grow fine over the winter? And how long do I let them grow before I chop them? Or can I just leave these pots alone and start the process of re-amending and cover crop in March?