This meditation on the nature of wrath offers two ways of dealing with on an offence. When the speaker is angry with his friend, he told the friend of it and his “wrath did end.” However, when he was angry with his enemy, he kept the anger hidden, allowing it to grow. His wrath, which is watered “in fears” and sunned ‘with smiles, And with soft deceitful wiles,” grows into the poison tree of the title. The tree bears “an apple bright” that the speaker’s enemy desires; the greedy enemy takes the fruit, even though he knows it belongs to the speaker, and eats it. The next morning the speaker is glad to see his “foe outstretch’d beneath the tree.”
"The Poison Tree" consists of four sets of rhyming couplets. Each stanza continues into the next, giving the poem a hurried, almost furtive tone that matches the secretive deeds done in darkness of the poem's content.
The obvious moral of this poem is that hidden wrath becomes more dangerous behind the deceit that hides it from its object. Possibly, the “Friend” mentioned in the first stanza is a friend simply because the speaker respects him enough to voice his anger face to face, whereas the “enemy” may be a potential friend who remains an enemy because the speaker keeps his wrath secret and nurtures it. There is a touch of irony, however, in that the poem ends with the speaker’s gladness over his foe’s death by poison. No final line refutes the secret nurturing of wrath, and in fact, the poem may be read as a guide for taking vengeance upon one’s enemies.
Some critics suggest that the apple symbolizes Blake’s creative work, which another of his contemporaries may have stolen and used as his own. If so, it appears the theft of Blake’s intellectual property ended badly for the thief (or at least Blake hopes it will).