I use empty plastic coffee cans with lids to take up space in big pots. The large pots get planted with annuals anyway, which normally don't need a lot of root space. As for revitalizing potting soil, I pull out plants at the end of the season and empty the soil into a large trash bag. That way I can stack the pots indoors to take up less room and store the bag of soil outside during the winter. In the spring, I mix the old potting soil with compost, perlite and worm castings and I'm good to go.
