Frost uses several forms of imagery to describe nature. In the first stanza, after setting the poetic persona's action and location ("I go through the mowing field"), Frost applies visual, tactile and locative imagery to describing nature. First he gives visual description, saying the mowing field is "headless" stalks after the grasses have been mown and harvested. He uses tactile (touch) imagery when he says the "aftermath" stalks are laid flat, like "thatch," by "heavy dew." He locates this "headless aftermath" flattened by "heavy dew" by saying it blocks the gate to the garden.
In the next stanza, Frost follows a similar pattern. He identifies the persona's action and location (in this poem, the persona and the poet are accepted as being one and the same because of the biographical elements surrounding its composition): "I come to the garden ground." Then he describes the birds in the weeds. This time, after an auditory (sound) reference to the motion of the birds' wings, he personifies the birds and describes them by a character trait: "sober birds." The description, "tangle of weeds," is both visual and tactile: you can both see the tangle and feel the tangle in your hands.
Stanza three is unique. The tree introduced metaphorically represents the persona who is himself "bare" and has "rattling" thoughts like the "rattling" last leaf that falls. "Bare" is visual while "rattling" is auditory. Stanza four returns the pattern of locating the persona. There is a visual image that accompanies the last "aster" that you are skilled enough to identify by yourself now. The third line has a more subtle visual image that takes a little more thought to pick out as it relates to all the asters. Can you find that visual image? [This is a lyric ballad in four quatrain (four lines) stanzas in iambic tetrameter with an abcb defe etc rhyme scheme.]