My irises are just not spreading on the shelf as much as they are in the bog.
I need plants that will grow out of a 6" water shelf. Parrots feathers and what else?
Irises, at least the few types I've used, seem to do best when their rhizomes are above the water line. Also they do seem to need a fair amount of fertilizer. In smallish pots that might mean adding fertilizer.more often than when in a bed. This is all to get the biggest plants, most blooms, spreading plants.
Plants became a bigger part of the my pond hobby than even the fish which surprised me. So one thing I did was stop using traditional shelves and make a bed instead.
The only difference is an edge so the entire "shelf" can be filled with cay or gravel or your favorite "soil". Plants like iris then have lots of room to get their biggest. These beds also solve the problem of wind blowing pots over and into the bottom of the pond and raccoons tipping them over. I keep the top of the soil a bit above water line so the plants have wet feet but not wet crowns. This results in zero risk of string algae in the plants. I really don't like string algae in the plants..
Beds can be as wide as I like and could be seen as a "bog" that's around the edge of some of the pond. Water from pump can go into the bog/bed and travel around the edge of the pond and flow out, as a short water fall if desired, and back into the pond. This does reduce a problem with round/rectangular bogs where water just takes a basically direct path (called channelling) from source to outflow and bypassing most of the bog. Not that I consider a bog to be a realistic filter, but still think they're great for plants.
Existing traditional shelves can be retro fitted with beds. This can also help reduce collapsing shelves...but now I'm way off the subject. Sorry.