In Carl Sandburg's poem "Grass," the speaker doesn't mention the sunshine at all, explicitly or implicitly. The poem is narrated from the perspective of the grass, which instructs an anonymous addressee to continue to "Pile the bodies high."
The grass lists various locations of historical battles, including "Waterloo," "Gettysburg," and "Verdun," and says that it shall continue to cover the bodies of the dead over time. The grass says that it will cover the bodies so well that in years to come people passing by will ask, "What place is this?" In other words, all traces of death will have been covered up.
You might infer from what the grass is saying, if we take a strictly scientific perspective, that it will need the sun in order to grow and cover the bodies. Indeed, the grass will need the energy from the sun, as it will likewise need nutrients from the soil, if it is to survive and grow.