I have an area on my property that is naturally wetland. It may be up to 8" of water in a really rainy spring but is usually wet mud to an inch or so of water most of the time. There are also a few deep spots, or spots I could digger deeper if I want standing (but stagnant) water 6-12" deep. I'm in zone 6A. The area varies from almost full sun to partial shade.

I'd like to add some marginal plants, I also am planting the traditional moist perennials but would like to try some of the more broader leafy "freshy" plants. There is some a fair amount of Arrow Arum (Peltandra virginica) growing there already. What I'd like to try is Golden Club (Orontium aquaticum) and Hardy Thalia (Thalia dealbata).

I'm not sure how well these will do and how deep they should be planted. The frost line for ground is 2 or 3 feet in this area but water never freezes that deep. I would think a pond wouldn't freeze more than 4 or 5 inches. The wetlands might be somewhere in between. If I put something with the top 6" down, I don't know if it would freeze that deep or not.

Any tips on how successful I'll be or how deep to plant these?

Most of the web site I find talk more about planting in artificial ponds. Both plants are supposed to be hard to zone 6 or 5 but I don't know if that's only if they are in running water.