Several colloquial phrases associate daisies with being dead: under the daisies, which means dead and buried, to push up (the) daisies and to turn one’s toes up to the daisies, which mean to be in one’s grave, to be dead.

 

The Clare Journal, and Ennis Advertiser (Ireland) of 9^th August 1838 published this poem:

TO MARY.

Ah! then Mary my jewel,
Why were you so cruel
To be off to the Sea, and leave L all alone,
To grieve and to sigh,
And at long run to die […]!
[…]
Then Mary my darling
Pray do now take my warning,
And make no more conquests with your chin or your nose,
For as sure as a gun*,
If we meet I’m undone,
And under the daisies you’ll cock up my toes.

(* The phrase as a gun has been used as an intensive or superlative expression in the sense perfectly, absolutely, especially in (as) sure as a gun, beyond all question, to a dead certainty.)

The phrase to push up (the) daisies seems to have originated in British military slang during the First World War. The earliest instance that I have found is from a letter that Lieutenant W. H. Roy, of the 6^th Battalion Worcestershire Regiment, wrote on 21^st May 1915 in a hospital in Boulogne, France:

I suppose in this sphere of life there are only two eventualities really. After a time it’s got to come that you either push up the daisies and enrich the soil a bit, or else you lie still and hold up a few bedclothes for a space of time depending on the circumstances. Anyway, here I am doing the latter with a mucked up right shoulder, but very thankful to be so cheaply out of a rotten business.

I have found a variant in an article about “the future of the Harbour Station site on the sea front at Ramsgate” published in the Thanet Advertiser (Kent) of 18^th May 1928:

Pushing Up Daisy Roots.

There would be members of the Council who would be no longer be [sic] members of the Council, but would be pushing up daisy roots before [the scheme] was carried out. It was not fair so to tie the hands of future generations. They would bear an undue proportion of the burden the Council were going to place upon them.

The equivalent French phrase is manger les pissenlits par la racine, literally to eat the dandelions by the root—cf. dandelion – pissenlit. It is first recorded in Les Misérables (1862), by the French novelist, poet and playwright Victor Hugo (1802-85); he wrote that the Paris urchin had his own metaphors:

être mort, cela s’appelle manger des pissenlits par la racine
(to be dead, that is called to eat dandelions by the root)