While critics suggest a number of themes for Frost's "After Apple-Picking," one statement of theme can be this: Apple-picking can be likened to the memory of writing poetry.
In every poem there is a controlling idea which helps to unlock the meaning of the poem. Certainly, there can be different interpretations which lead to the finding of different controlling ideas in Robert Frost's poem about the harvesting of apples since the apple can be seen as a symbol of different things. But, one interpretation is that the apple is the fruit of the poet's efforts, the finished poem.
One argument made by critics is that "After Apple-Picking" is an allegorical poem for Robert Frost's career as a poet with the theme of Memory. This theme is most pronounced from line 25 to the end of the poem:
For I have had too much
Of apple picking: I am overtired
Of the great harvest I myself desired....
Looking back on his career as a poet, Frost remembers his desire to write poems of worth, some of which were discarded-- "Went surely to the cider-apple heap"--but there were many that were achievements--"Of the great harvest that I myself desired." Now, he is exhausted from his creative efforts as he approaches sleep, always a symbol of death for Frost.
As sleep approaches, the poet's memory will recall for him the "apples," or ideas, which he began but discarded, and his successes. He is also concerned about the sleep state that he will enter, exploring ideas of what lies beyond death--"whatever sleep it is." Is it like the woodchuck's hibernation and one awakens to a new season, a new life? Or, is it "just some human sleep" in which he will have memories?