What is the connection between the Moon and the Yew Tree in Plath's poem, The Moon and the Yew Tree?

The two entities, the moon and the yew tree operate in tandem and refer to one another. In the final stanza of the poem the yew tree takes on more prominent reference than in the earlier portions of the verse. While the moon is described as “bald and wild” (27), the yew tree is described as existing likewise outside the rituals of the church. The final line of the poem expresses this sentiment forcefully: “And the message of the yew tree is blackness — blackness and silence” (28).