in Just- spring when the world is mud- luscious (1-3)
These lines almost seem to split along a vertical line. The phrase ends mid-line 2, which the long space between "spring" and "when" allows us to see.
luscious the little lame balloonman (3-4)
That’s a lot of "l"s in one line! Have you noticed that when you pronounce an "l," you close off your mouth? That seems to run counter to the sorts of opening and growing that goes on during spring.
whistles far and wee (5)
The spaces between words communicate almost as much as the words themselves. Here, the spaces literally enact how far the whistles travel.