This poem isn't set in a specific place, but its imagery definitely makes some beautiful settings sprout in our minds. There's so much talk about roses that we can't help but imagine a gorgeous garden that's just bursting with them. It's hard not to with lines like "you open always petal by petal myself as Spring opens/ (touching skilfully,mysteriously)her first rose" (7-8). Since it's a passionate love poem, we're imagining red roses, but, hey, other colors are nice too.
There's also some talk about the seasons in the poem, so we see the speaker and his lover standing in the garden with time passing around them. When spring comes around, the bright flowers gently unfold, and when winter comes they quietly close with "the snow carefully descending" around them (12). The whole time, the speaker stands absolutely still, gazing intently into his lover's mysterious eyes.
In that way, then, the most steadfast setting of the poem can be understood as the relationship between the speaker and his lover. It's not only the entirety of the poem's subject matter, it's also the setting against which the speaker's observations and declarations appear. Love—is there anything it can't do for us?