The poem "City Trees" by Edna St. Vincent Millay conveys themes of resilience, beauty, and the ability to find strength in challenging environments. The city trees symbolize enduring nature against the backdrop of an urban landscape, illustrating how life can flourish even in the most unexpected places. There are also undertones of the contrast between the artificiality of the city and the organic growth of trees, highlighting the tension between man-made structures and the natural world.