Some of the popular peat-lite mixes are real nice out of the bag but they begin to collapse within a few months. If it's been used for a full season (or year) I wouldn't recommend reusing it for your containers.

You should look for soil that is not peat based. Or look forward to changing it every 6 months to a year.

Yeah, you should toss out your soil if you plan to use it in containers. I think it would be fine for plants outdoors in the ground where mother nature can help.

I have tried several ways to rehabilitate used potting mix. Starting with bark based mixes and screening out the fines, adding new bark and dolomite. The result was less than satisfactory, so now I bite my lip and use only new mix in my containers. Al