When I go up through the mowing field,
The headless aftermath,
Smooth-laid like thatch with the heavy dew,
Half closes the garden path.
And when I come to the garden ground,
The whir of sober birds
Up from the tangle of withered weeds
Is sadder than any words
A tree beside the wall stands bare,
But a leaf that lingered brown,
Disturbed, I doubt not, by my thought,
Now the birds here in this context, is a metaphor for humans. 
 Now that we got that cleared up, the withered weeds can be a metaphor for what has happend to Robert Frost’s appearance. His outer if you will. (One of weeds many diffeent meanings are:(obsolete) Clothes.) so the clothes are his appearance.
A Late Walk