Idiom used to imply someone who is Dead and whose body is fertilizing plants (sunflowers). Hence you are "pushing" sunflowers up
from the ground.
Popularly, the idiom was Pushing Daisies. This variation was
inspired by a brave Ukrainian woman who encouraged Russian soldiers to fertilize sunflowers, during the Russian
invasion of Ukraine in 2022.
Pushing Daisies was the idiom. Now it shall forever be Pushing Sunflowers.