You can actually grow mint in the ground. It takes a bit of a trick, but you can definitely do it.
But first, a personal lesson on why people tell you not to plant mint in the ground (and yes, I knew better, but life happens and I didn't actually intentionally plant this):
This is my apple mint patch, which started by accidently dropping some minty debris and thinking, what's the worst that could happen? This. This is what can happen.
As you can see, it has engulfed potatoes, rhubarb, strawberries, and raspberries. It has received no care. It has out competed the invasive species that was there (bindweed), and replaced it. It's about 4 feet tall in the center, 5 feet wide, and 7 feet long. I really should do something about it this year.
And here's my other mint patch which is lest than 10 feet away, started at the same time, looking a little rough because I pulled some out to give a friend the other day (well, and it's shaded, and that corner of the yard is pretty weedy- but still! It gets the idea across!)
Take a closer look at the soil between the pots:
Notice something? Something like the mint not escaping? Yeah, there's bindweed that's gotten in, but ignore that for now*.
Mint.
In the ground.
Contained.
I also know someone who planted theirs in a chimney flue bricks, and it too, has not escaped- even after 5 years.
Why is this important? Well, because mint likes it moist and pots dry out quickly (which means that if i had to keep an eye on it, it would have died 4 years ago).
But if you half bury the pot, the roots (but not the runners!) go down and out and can use the moisture in the soil. I actually lifted these pots up a while ago to check, and they had sent roots down but not runners- and it has been multiple years.
Meaning I haven't had to water this mint. Not even during the 100+ weather days, and we have a summer dry period where we don't get any rain for months.
Now, truly, I was a bit concerned and not trusting of my own idea when I started this, so let me draw a picture of what this system actually is, for folks like me who think it's too good to be true and want some extra insurance:
So, as you can see, I didn't put the pot straight into the ground- I actually mostly buried a bin (that had holes in the bottom for drainage), and planted mint pots into that. I have not seen any mint escaping from the pots, but that's there, just in case.
*bindweed/perennial morning glory is awful. If you see it starting in your garden, remove it without hesitancy or mercy. Get every little bit of root. It's harder to get rid of than English ivy or Himalayan blackberry.
