In her poem "Poppies in July," often referred to as a confessional poem, Sylvia Plath opens with a question posed to seemingly harmless poppies, asking if they really "do no harm," if they really are harmless. Plath committed suicide in February 1963, and her confessional poems portray her own state of mind leading up to her death. Opiates are derived from poppies, and opiates can do a great deal of harm when misused since an overdose of an opiate can easily kill a person. Not only is she contemplating using opiates to commit suicide, the question shows the doubts in her mind. People commit suicide because they question the rightfulness of their existence. Opening with a question portrays how much she is questioning her own life.
Her state of mind is further conveyed in her metaphor likening poppies to "little hell flames." The Christian religion considers suicide to be a mortal sin because taking one's life into one's own hands is the same as playing God--only God has the authority to choose who dies when. Hence, Plath is looking at the poppies, or the opiates produced by the poppies, and contemplating suicide, which makes her think of the fires of hell.
Hence, as we can see, the poppies she is looking at are not truly harmless in her mind, making her open her poem by contemplating their dangers in the form of a question posed to the poppies.