Read "Duality" at The Eldritch Dark:
Although it was most likely written in 1915 or 1916, several years later (1923) this poem would become one of Clark Ashton Smith's (CAS) early appearances in Weird Tales magazine, and his association with that publication would become a permanent part of his literary reputation. The poem was re-titled "The Garden of Evil" for that appearance in Weird Tales.
What intrigues me is the original title: "Duality". As any good poet does, CAS seems to have chosen his titles with great care, and so I can't help but read this poem while seeking to understand that particular choice by the creator. From the very first line, CAS clearly presents his argument:
Thy soul is like a secret garden-close,
A "garden-close" suggests an enclosed space, in this case a secret, enclosed garden. But this poem is addressed to an unknown someone, and that secret garden is a metaphor for their soul.
Later in the poem, we encounter "the cypress-perchèd nightingale". And I think that phrase is the key to the poem, and the source of the duality expressed in the title. The nightingale has symbolic associations as a link between love and death (see for example John Keats' "Ode to a Nightingale"). The placement of the nightingale in a cypress touches on the association of that tree with the underworld in Greek and Roman mythology.
The setting of this poem is someone's soul, rendered with sets of conflicting symbols. The bergamot and the rose have vibrant, life-affirming suggestions (think of the intense citrus scent of the former), but these contrast with the poisonous aconite and mandragora.
Right at the very end of the poem, CAS gives us a striking image:
...the silver-bellied serpents pale
Their ruby eyes amid the blossoms ope,
To lift and listen in the ghostly gloom.
The serpents have heard the nightingale's song, and although our scene is wrapped in "ghostly gloom", it's important to note that those same serpents have opened their eyes "amid the blossoms". As noted above, those blossoms are a combination of beneficial and inimical plants.
In "Duality", CAS has given us a gorgeous portrait of a real human soul in which the good and the bad and always present, and the balance between those elements is always in flux. Perhaps this poem has a tilt toward the melancholy, what with "the moon's phantasmal fingers" and "the marbles of a hidden tomb", but the melancholic aspect of these lines is not the totality.
Experiencing a poem like "Duality" is the reward for my long journey through the complete poetic works of Clark Ashton Smith. This is not among his most famous verses, but it is outstanding, and my life is the richer for having read it.