Don't know if astilbes are OK actually in a bog, How about a Royal Fern? They can look spectacular.

Hi Lin. Maybe your bog garden was too wet for the rheum. The first rime I had one I set in too wet an area and it was like yours. Once lifted and moved to just a damp area in the border, it was fine, I'm sure it will survive if you move it to somewhere just damp. I have a few now, all doing well in these conditions. Maybe aquatic marginal plants would prefer your bog.

My Astilbe is planted in a small bog garden, next to the pond, and is doing very well.

Steragram, I already have two Royal Ferns around the ponds so don't really want more.
Daunsaunt - I'll do as you suggest and move rheum to edge of bog - a nuisance as it will be a squeeze! I already have lots of marginal aquatics around the middle pond - the cottongrass is quite prolific & so deeply established that it can't be removed but looks lovely with all its fluffy tops.
Cutsandgraz I think I might try an Astilbe as have had no success with them in other parts of the garden and often thought they might prefer wetter/damper conditions and good to know that your's is doing well.
Thank you all,
Linmar

Hi Dawn,
I rushed out and lifted rheum to replant but it had only one long root and might have died. No wonder really because as soon as it lost a leaf I watered it thinking it needed loads of water! Will just wait and see as its in a drier position.
Linmar

Hi Lin, I'm sure it will be fine. When I lifted mine from the boggy area I set it on spare ground next to the greenhouse and was amazed how well it came up the next spring. I moved it again then, pretty tough and forgiving.

I have recently discovered Water Figwort growing in the boggyarea of a pond. I had one or two in earlier years but pulled them out & binned them. This year I decided to investigate further and quite pleased I did as the little hover bees love them and they are quite unusual.
Linmar

Sounds lovely, I'm not familiar with it but as a native perennial, perfect. I had a Rodgeria on my pond edge which has struggled for a couple of years so I've lifted it and its now in a big pot - has a new leaf :)