Water logged

I am in the process of creating a 2 acre garden from a field. I could do with some help on what to under plant in the Hazel nut grove. The added twist is that we are in a flood plain with clay soil, so in the winter the ground is soggy to say the least! and in the summer (well usually) the ground is as hard as marble, with no drainage except for what we add ourselves. In the spring and Autumn the plants have to contend with flood water.

Oooh how exciting - I'd underplant with narcissus pseudonarcissus http://www.kew.org/plants-fungi/Narcissus-pseudonarcissus.htm, the original 'wild' Brtish native daffodil, native primroses,  and English bluebells for the spring.  They ought to cope fine with the conditions but if you're worried, can you create banks for the primroses (and maybe some wild-type violets too)?

For summer I'd put in wild flowers such as cow parsley,  pink and white campion, and wild foxgloves, and some dryopteris ferns and hardy geraniums, and some honeysuckle.  

For the autumn, some clumps of arum pictum, and tall teasels coupled with the seed heads of the cow parsley and the coloured leaves of the geraniums and the hazel will look lovely, and in the winter the frost on the ferns, honesuckles and hazels will be fantastic.

I'm getting carried away 

Just had an idea - have you a lower area where you could create a pond for the nut grove to drain into - then there's loads of other marginal stuff you could plant,. wild water mints, purple loosestrife - watch out I'm getting carried away again and anyway, you've probably thought of a pond anyway 

Last year I planted 40 wild primroses but only one survived It was just too wet. I didn't think about banking them up though. Thanks for that tip I'll try again with a few and see what happens. I was thinking of planting pheasant eye narcissus poeticus recrvus but wondered if they would rot in the wet?
I had planted Hellebores as well but again the water rotted them away. I know that it has been an exceptional year but it's also been a little disheartening.

Lovely ideas for the summer and autumn I had been thinking of having it mainly as spring planting but I feel that like you I will get carried away.

Yes pond already thought of two already in situ and bog garden in the plans that I hope will help.

Thanks for your thoughts.

I think the wild daffodil (narc. pseudonarc.) might cope better with the wet than poeticus, and if you look at where wild primroses grow it's mainly on hedgebanks and the sides of ditches - they don't mind being wet, but not for long - so if you can have some raised banks for them they might be happier.

Something else that certainly grows in damp places, and is so very pretty, is Lady's smock http://www.healeydell.org.uk/files/Ladys_Smock.pdf,  and also Meadowsweet http://www.purplesage.org.uk/profiles/meadowsweet.htm will do well there I'm sure.

Good luck 

As DFA mentioned planting primroses on a bank, I remembered the wonderful Christoher Lloyd writing about this - he advised planting them at the top of the bank, and their natural method of increase would encourage them to spread downwards. We have wonderful stretches of the wild daffodil here along the banks of the rivers and streams, so would tend to agree with DFA about that species, but I've also read that they can be a bit slow to get established in gardens.
As you've got 2 acres to play with, have you thought of gunnera?