I repotted mine in those long plastic window boxes they sell at wal-mart or k-mart for around $5.00. They are only around 5" high, so you will have an extra inch of water to flow over the top.

Good idea.

So I guess because the plants are in water they don't really need that large a container? I guess that probably depends on the species, eh? Can you use an osmocoate type fertilizer in such a situation? I think I read somewhere you can use clay to ball up some fertilizer for a slower release.

I took long brick like rocks and lined the shelf to make a wall and filled it in with pea gravel and plant directly into it. I detest looking at pots.

I use 8" terracotta azalea pots. I do sink them on the bottom in the winter so they don't freeze and crack. The plants don't mind spending the winter on the bottom. I wanted the terracotta for additional weight. I do have some gravel in the bottom also.

Here is a link that might be useful: {{gwi:209938}}

I don't use fertilizer in my plants and all mine are doing fine. Sorry, can't help with that part of your question. Anyone?

I plant almost all of my marginals directly in gravel &/or rocks, for the same reason as buyorsell mentioned. I'm not sure how wide your shelves are, but you could also put larger rocks down and create planting pockets behind/between the rocks. Just line the pockets with cocoa fiber, etc. (I use leftover scraps of pond liner underlay) and fill in with regular garden soil (not potting soil). My lobelia cardinalis seems to prefer this method but maybe someone else has had good luck with it in the gravel?

I don't fertilize mine either, but if your pond is fairly new, a few aquatic plant tabs (or a similar slow-release fertilizer) probably wouldn't hurt.
Sherry

I have rushes and Lobelia (among others) in my pond, no containers (soil rinsed off, plopped right in the water on a plant rack DH made to extend across the pond and supported by the plant shelves on both sides). My mosquito fish provide enough "fertilizer" for them, it appears, since I've never had to feed the plants.

Brenda