They are indeed perennial and the only thing you will need to do if they like your garden is to keep removing the root runners as they are invasive.

Yes they are perennial,
Here in fance they are given on the first of may as a friendship token,
they are very late this year at our gite i noticed this morning they are still out.

I have these growing under a big cherry tree, and it took some time to get them established, but now they are invading the lawn, so, a beautiful plant, but can turn into a nuisance. I think this question has reminded me that I need to get out into the garden and dig it up. No doubt it'll be back again next spring.

Gattina,
reminds me of a poem,
goes something like this,

Good gardens are never made by sitting sunning your
self in the burning sun or hiding in the shade.

Be careful- they spread like wildfire.

Ah, Dungy, but where's the sense in gardens that you never have time to sit and enjoy when there IS any sun?

I know too many folk who are so busy 'working' in their garden that they never take the time to just sit and enjoy it. There has to be a balance of working and enjoying or the whole exercise becomes pointless. Often I think that the owners of a garden only see the weeds and what needs doing whilst visitors see the flowers and the beauty of nature.

Exactly!

thankyou all for your help xxx

You're welcome Claire