You can do it to save money, but I'd apply certain conditions... Was it a good-quality mix to start with? What size are these pots and have you already removed old plants/roots to see what you have to work with? If your pots are large and the 'used soil' is of sufficient bulk and clean of debris, then it should work. Especially if you can top it off with some fresh mix (I use Pro-Mix for potted plants). FWIW, I learned long ago that to have success with container-grown plants, I need to give them a constant supply of weak plant food, and it's one time when organic ferts won't work as well, so I use a weak solution of Miracle Gro.

Thank you for the reply, party-music. Just what I was hoping to hear. I do use Pro-Mix also, and it will be certainly possible to add some fresh to the top of re-used stuff. The new pots are 10-gallon grow bags (new experiment this year). Grateful for the fertilizer tip as well!

Now, if we can just get through the next four days of close-to-freezing at night temps!! (Not that it is time to plant outside yet in any case)