I personally wouldn't use mint as an understory. But if you want to, you might want to keep the two mints separated. Otherwise they will intertwine with each other. One issue that would come from that is if one mint was more vigorous than the other (most likely the chocolate mint), it might crowd the other out. And whatever you do, don't let them seed because not only will they spread but you will have mutts (cross pollinated and unlike the originals).

Edited to add: My chocolate mint is about 18 inches tall right now because I haven't harvested it yet this year. So the height of the mint is something to take into account as well. (Athough the height can be managed.)

Rodney

This post was edited by theforgottenone1013 on Thu, Jun 19, 14 at 18:08