Ah, Spring. It's that magical time of year when a "young man's fancy lightly turns to thoughts of love" (that would be Tennyson's "Locksley Hall," line 20). Oh wait, wrong Victorian poet. This is absolutely not a poem about love. It's a poem about coming to terms with your own mortality and death.
So why does the title have the word "spring" in it, anyway? We usually associate "spring" with new life, hope, and love (partly because of poets like Tennyson!). The poem takes place in the fall, when the trees are losing their leaves, not during the spring. Maybe it's because the girl, Margaret, whom the speaker is addressing, is in the "spring" of her life—she's only a "young child," according to the dedication. But even though she's young, she's already starting to realize that she will eventually grow old and die. So the poem is about the juxtaposition, or contrast, between youth and age, innocence and knowledge, spring and fall.
The word "Spring," then, makes sense. But why choose the word "Fall"? After all, Hopkins could have chosen the more typically British word "Autumn" for his title instead of "Fall." Perhaps the word "fall" could suggest the idea of Adam and Eve's "fall" from grace in the Garden of Eden (see the "Symbols" section for more on that). That might make sense, given that Hopkins was a devout Jesuit priest. If so, it sheds a new light on the idea of spring here, which can also refer to little Margaret's budding innocence, and the impending decay of that innocence with the recognition of her own human mortality. Bummer.