The phrasing and pauses here seem simple and straightforward: periods represent the end of a phrase with full stop pauses; commas, brief pauses within conjoined phrases; long lines represent less rhythmic phrasing; shorter lines, more rhythmic phrasing. Yet, analysis and close reading show this is not the whole story. Layers of intricacy unfold like gardenia’s petals before the attentive reader.

Space doesn't permit a detailed analysis, but I'll give you enough that you can find your way. There are at least eight elements to consider in analyzing phrasing and pausing: vowels, consonants, commas and periods, enjambment, pace (speed of utterance), volume crescendo and decrescendo, tone, emphatics. Phrasing can have two meanings: (1) as in grammar, the choice of poetic phrases used, like "a gone-time"; (2) as in music, the division of larger unit of thought into smaller segments. Since you ask about pause and phrasing, I suppose you to mean the music related definition.    

First note the irregular yet consistent pattern of short pauses (P) and full stop pauses (FS). The first lines have these pauses: FS, P, P, P, P, PP (2xs P), FS, 2xs P, FS, P, FS, 2xs P, FS. There is no regular pattern, but the options are consistent: a full stop, a comma, or two commas. Next note line length: some are longer, some shorter. You will note the less rhythmic phrasing of the longer ones and the more rhythmic phrasing of the shorter. For example, compare the two following lines:

Shilly-shallied across meadows,
[...]
And left me cowering in monstrous shadows.

Next, note the use of vowels and consonants, enjambment and emphatics. Vowels and consonants create mood and tension or relief by their characteristic qualities. For instance, voiced and unvoiced plosives and glottals /b d, t p; g k/ may heighten tension and mood as in "Brick by greedy brick," while shortening or quickening phrasing. In contrast, the soothing quality of open vowels /oo a e/ and sonorant consonants /m n/ as in "I remember when life was good," elongates or prolongs phrasing. In the first, phrasing is affected by the staccato rhythm, while in the second, phrasing is affected by the prolonged pace.

Enjambment, the absence of line-end punctuation, eliminates the pause between lines. Patten employs it in a few places, as in two lines below:

Like drunken giants
They vomited their poisons into me.
Tonight
A scattering of vagrant bluebells,

The line "Tonight," besides illustrating enjambment, demonstrates the use of emphatics to emphasize a point, mood, tone, or rhythm while also effecting phrasing and/or pausing. For instance, both the enjambed lines above curtail phrasing while eliminating the established pause pattern. This way, and in conjunction with vowels and consonants, the pace (speed of line reading/delivery) is increased or slowed down. Similarly, volume is influenced so it rises or lowers, crescendos up or decrescendos down. Phrasing is affected by both pace and volume since all are directly related to breathing and breath control. Below is a sample of pause and phrasing analysis notes, which you may find useful:

Were my secret agents.      FS
It was a sweet time, a gone-time,     2xs P  --  slow pace, decrescendo
A time before the factories grew,    P  ---  dark mood, more decrescendo
Brick by greedy brick,      P  ---   pace: staccato  b-k-b-g-d-b-k
And left me cowering in monstrous shadows.      P  ---  emphatic /c m sh/