I think they like their crowns above the surface. I grew them in bogs and on the shelves of my pond and they did very well. I just planted them in pea gravel and they worked well as filtration. Kept a lot of my algae down too.
Good luck :)

I have a couple in a stream only partially submerged similar to the way I have some elephant ears in a shallow section of my pond.

Hi BT. I've been using garden plants in my ponds for years. There are little containers out now that float on top of the pond like little gardens and a Hosta would work perfectly there. No dirt, just the roots in the water and see how your Hosta will eventually cover the whole container.
In my waterfalls, I have used parrot feather and impatients and they both look great.

Your's Koily, Lorraine

Lorraine can you tell me where you found those baskets? Thanks everyone for your help.

Here in Southwestern Ontario Canada we got to Moore Water Gardens in Port Stanley or the Bloomin Bog in Ilderton for this product. The plant baskets are inside a flat piece of styrofoam that float on the water. Actually, I would get some styrofoam, make a hole large enough in it to put the roots of your Hostas and see how that works. Might save you some money.

Lorraine

I bought two at Vandermeer Nursery and then made two more by cutting a ring out of styrofoam and covering it with black electrical tape. Worked great and lasted longer than the bought ones, actually still using them.