I've reused the old pot with lemon balm roots (Melissa officinalis), cardamine seeds and I've put an onion inside. An onion with leaves becomes bitter, however leaves alone are quite tasty.
Why not? Lemon balm is not cheap, trying to revive it saves money :) The rest of herbs have been planted just for fun (and good sandwiches, finally).
Quite often we have two or three windowsill gardens, usually with some fresh herbs.