Cherry blossoms
The cherry blossoms are a powerful symbol of transience and the fleeting beauty of the world, representing the brevity of life and the importance of living in the present moment. The narrator's desire to see the cherry blossoms is a reminder of the importance of appreciating life's small, precious moments before they pass by.
Time
The three years that the narrator wishes to experience are symbolic of the brevity of life, as well as the narrator's desire to make the most of his time on earth. The number "three" also has symbolic significance in many cultures; it represents wholeness and completion.
Earth
The earth represents the cycle of life and death that everything—from humans to other animals, to whole ecosystems—constantly renews itself. The narrator's desire to "plant" himself on the earth and be "one of the creatures" illustrates his desire to be part of this cycle and to embrace the natural world.
The Forest
The forest symbolizes the passage of time and the cyclical nature of life across the earth. As the narrator, who is a fairly young man, observes the trees in the forest, he is how quickly life, which is incredibly brief, passes by.
The narrator's age
The narrator's youth is an important motif that runs throughout the entirety of Housman's poem. It represents how quickly life comes and goes and how important it is for humans to seize the moment when they are able to.