leaves of gunners turning brown

i planted gunnera a few weeks ago they were doing great but then all the leaves gone brown shrivelled up.we had a bit of frost at night but i taught they were hardy and didnt cover them.frost gone now but plants looking half dead.most of leaves brown and new leaves coming up green at moment just afraid the same will happen them.i have them planted in a shady aknove spot but they still get sun,i water them regulary as i know they like water,dont know what im doing wrong can anyone help?thanks

They come from South America and aren't frost hardy in my experience until the foliage is much more mature.  try giving it a good feed of liquid tomato feed to boost it in case the roots are still OK and can put up new shoots.

I've tried growing these in my garden but we suffer cold winters so it needs a blanket of 3' of compost over the crown to keep it safe and that's no guarantee.  I think the latest is a goner this year.

as Obelixx says, more mature specimins are more likely to survive. As soon as you get a threat of frost, cover the crown with fleece, newspaper anything to keep the cold air off of it. They like to be in boggy soil. so keep it moist. But the crowns aren't that keen on being buried. In Autumn bend the leaves over to protect it and cover with bracken. I have one I bought 3 yrs ago, it's in my peat bog and is surviving, even through the really bad end of 2010. My huge one is able to take care of itself. but the little one I just ensure the frost cant get to it.

When I grew them, 1000 feet up in the Welsh hills ( so cold!), I used to remove the leaves in autumn and pile them up over the crowns, and leave them covered until around now. As Obelixx says, the budding crowns are tender. 

I am 1000' up welsh hill and yep it is cold. The leaves of my big one, fold over and fall on the crown without my help. But I do check that they have fallen in the right place. The buds once broken with leaves pushing thru' are when they are at their most vulnerable.