They scatter on an empty sack
That is a rewriting of a hokku by Yayū. It is of course a spring hokku.
There are, as I have mentioned many times, two kinds of harmony in hokku: harmony of similarity and harmony of contrast. This verse has the latter. It shows us the pinkish-white blossoms of the plum drifting down through air and falling on an empty charcoal sack, which is black with dust from the charcoal and filthy-looking. The whole point of the verse is in the visual contrast and the feeling of “high” beauty in the plum blossoms contrasting with “low” in the empty charcoal sack.
This mixture of conventionally poetic subjects with “earthy” subjects is characteristic of hokku, quite different than the earlier and longer waka (essentially a hokku plus two extra lines in form), which used only poetic and “elegant” subjects.
This reminds us of three main aesthetic characteristics of the hokku — poverty, simplicity, and transience. All are seen in this verse.