Hi. I grow spearmint, but not in water, and it will die back at first frost. It does come back in spring tho' as long as the roots were protected. :)

I took cuttings of peppermint and grew them in gravel filled pots in the shallow end of our pond this year. It rooted quickly and did better than the aquatic mint I bought. Don't know if it will survive the winter here, but if not I'll just take more cuttings from the patch in the yard.

I've grown Choc Mint in my pond for the last 2 years, I cut off stems from the original plant and stuck them down between the rocks and around the waterfall. These were unrooted cuttings, didn't take long for them to root, they do great and come back every year. They are just as vigorous a grower in the water....

Micky