I presume you mean the perennial Helianthus. They have survived here for over 20 years now, thugging away in one of the borders.

Yes well something is going on even if I prepare the planting hole correctly they never seem to last I think it's not enough moisture in summer and too much on winter I'm particularly talking about moerheim beauty type german hybrids the green fleshy perenial types

Moerheim Beauty is a Helenium not a Helianthus.
We cannot grow any of them here except Sarin's Early. They do not even last one season.

Strange...I found Helenium grew rather too well in my clay.

We are not on clay, we are on sandy, silty peat.

Owlboggy was right I was talking about helenium rather than helianthus that seem to do ok here and can get to size with enough rain. I live near wisley in South East and we just don't get enough rain in summers now if truth be told add to that clay (there was a brick factory here at one time) which dries out and cracks pretty fast but all in all I done what I can with the garden by adding as much organic material I can find around never composing instead just cutting down and leaving in situ so can't complain but their are certain plants a lot that struggle for lack of water in spring /summer and rotting in winter. Here's a rundown heleniums,rudbeckia,penstemon,bulbs,cultivated aquilega,delphinium ,salvia(most) ,digitalis,cosmos,satrangi,antirrhinum,agastatache,lupins,Dahlia,perovskia,crambe,achillea,nigella,guara,echinacea,poppies, are just some of the no shows or strugglers...

Reading through that list I would agree that most of them do prefer a more even distribution of dampness. Ie. damp in Summer and dryer in Winter.