The final line of "Written at the Close of Spring" by Charlotte Smith is "And sad I am, my heart is sick to-night!" The speaker laments the end of spring and the coming of summer. The poem expresses the speaker's melancholy mood as she observes the beauty of nature fading away and the onset of summer, which she associates with heat, drought, and the withering of flowers. The final line is a reflection of the speaker's sadness and sense of loss as she contemplates the end of spring and the transience of life.