Simon wrote
I've given up on trying to rescue a 10 x 8ft area of lawn at the bottom
of my garden. It just wants to stay wet for 11 months of the
year...thanks to my deep Berkshire clay. It had anyway become populated
by boggy weeds so I have decided to let it be a bog garden. I didn't
like the weeds though so I have removed the topsoil, complete with most
of the weeds and roots and what turf there was and I now have a clear,
brown patch with puddles. I would like to beautify a bit while planting
some bog-lovers and would be grateful for advice.

Firstly, I'm all ears for plant recommendations. I want some height
mixed with some colour, but I don't like anything that looks like giant
rhubarb (threw some of that away). I guess I want it to look at least
semi-cultivated/planned rather than some bog gardens that I have seen
which are more or less overgrown with the kind of coarse leaves that
I've just dug up.

Firstly, Yellow Iris is a native plant and is a thug, and a none to
attracitve one too. No, go for Iris sibirica and Iris laevigata, both have
beautiful flowers, both like the wet, both have nice leaves in summer and
are non invasive, quality plants. Come in lots of colours too although I
prefer the dark blues of sibirica and the deep purples of laevigata.
Other good looking plants for bog gardens are.......
Zantedeschia aethiopica (depends where you are, grows well here)
Primula prolifera (Candelabra primula)
Osmunda regalis (Royal fern, tall)
Astilbe
Dactylohriza maculata or fushii (probably difficult to find and establish)
Hosta (not if you have lots of slugs and snails)
Polygonum (will spread)
Filipendula

Next, should I improve the soil or just leave it be? It can clearly
support healthy weeds.

Improve it in what way, clay soil is fertile soil. Perhaps mix some good
loam in to break up the top clay layer but no manure or compost or you will
change things.

Presumably I will need to make planting holes - but I'm thinking these
will just fill with water. Maybe I should plant in baskets?

Bog garden plants like bogs, so why are you concerned about holes filling
with water?

Should I edge the area, maybe with rocks or sleepers and/or some
marginal plants?

Up to you, but these ARE marginal plants. :-)

And to prevent the weeds returning could I cover with a
weed-suppressing fabric, mulch and/or gravel/slate/shingle?

Yes, if you want. A mulch would be better as it will allow the plants to
push it aside and spread a bit.

And finally, the supreme irony: for the one month of the year when this
area dries out, should I add water?

Yes, bog plants can't take dry very well.

--
Regards
Bob
In Runnymede, 17 miles West of London