What's an analysis of the symbols in the poem "Mariana"?

The poem "Mariana" by Alfred, Lord Tennyson in essence is a poem about isolation. It describes a woman, the poem's namesake, who feels cut off from modern society, and this lack of connection to the world around her causes her to wish for death. If we work with the theme of isolation, it is possible for us to isolate several symbols throughout the piece that contribute to this overarching concept. 
The "blackest moss" on the flower pots and "rusted nails" in the first stanza both symbolize the slow passage of time and the effects it has on immobile or stationary things. The flower pots, untouched, have begun to gather a black moss, just like the old nails have begun to rust due to lack of care and upkeep. The woman who is the subject of the poem feels much like these objects, which have degraded over time as they are left alone. 
The poplar tree, first introduced in the fourth stanza, symbolizes the life that exists outside of her room that she feels so separated from. While she can see it from her window, she cannot touch it or experience it from the confines of her home. Her deepest interaction with the poplar is through the shadow it casts into her room in the moonlight, a shadow which symbolizes how her lack of connection to the outside world brings darkness into her life. 
The door in the second to last stanza essentially symbolizes a portal through which she could enter the world if she so chose. However, the door is marked by dark and eerie imagery, representing her anxieties about connecting with the outside world. It is marked by its creaking hinges and the old faces she sees glimmering through it, which only work to further her distress at being shut away alone in her room.