Love those blocks as well. Where did you buy them?/Find them?
I'd love to get some like that.
"The rule of no realm is mine. But all worthy things that are in peril as the world now stands, these are my care. And for my part, I shall not wholly fail in my task if anything that passes through this night can still grow fairer or bear fruit and flower again in days to come. For I too am a steward. Did you not know?" Gandolf
Peppermint roots will take over an entire bed and find ways to get into the next. So I advise planting it a separate container that is designed to be escape proof.
What has worked well for me is the top cut off of a plastic barrel on cement blocks. The mint likes lots of water so I keep it partialy flooded but remove one of the caps during the rainy season so it is not completely flooded.