I think it would be nice to read more of H.P. Lovecraft's poetry in August, since that's his birth month. Similarly, September is the great month to read the poetry of Stephen King. February is Women in Horror Month, so you might look at the poetry of Helen Marshall, Stephanie M. Wytovich, Jeanine Hall Gailey, Marge Simon or Roz Kaveney. There's more than plenty of reasons to read horror poetry year-round.
Overall, horror poetry often gets a short shrift in this modern age, shoved aside in favor of horror films, video games, short stories and novels, among other mediums. I think that's a pity considering that the roots of really distinctive American literature and the modern horror genre can be traced in large part to the work of Edgar Allan Poe.
Where would the state of US poetry be today if we didn't have "The Raven"? I think it's important that we not take for granted Poe's contribution towards creating a unique American cadence and grammatical aesthetic through his work. Certainly, he's not the first nor the terminus, but his role in popularizing interesting approaches American poetry and employing the macabre should not be denied.
I feel it's also important to remind poetry fans of other great writers from America who have written horror poetry so that we understand the form includes more than just Edgar Allan Poe.
Take the creator of Conan the Barbarian and Solomon Kane, for example. Robert E. Howard left behind a good many horror poems such as "Cimmeria." To be fair, some verged on doggerel, but he had many bright flashes as a poet, and did not shy away from dark and tragic subject matter.
James Weldon Johnson was an early African American author, educator, lawyer, diplomat, songwriter, and civil rights activist. He's perhaps best known for God's Trombones: Seven Negro Sermons in Verse, but he also has horror poems such as "The White Witch."
Of course, H.P. Lovecraft has an impressive corpus of poetry, such as his cycle, "The Fungi from Yuggoth," which helped pave the way towards creations who would appear in his later prose such as the Mi-Go from "The Whisperer in Darkness."
The poet Ogden Nash is mostly known for his light poetry, but he had horror poems in his body of work such as "The Wendigo." Some might say we shouldn't consider horror poetry anything with a comedic flair, but by that logic, a film such as the Evil Dead or the Nightmare on Elm Street series would also be disqualified from the genre.
One of my other favorite authors of Weird literature, Clark Ashton Smith was also a prolific poet. You can take a look at poems of his such as "In Thessaly" and see how he approached the dark and supernatural in verse.
Of course, a discussion of horror poetry should also note Stephen King's ventures into the form. His poem "The Dark Man," eventually led to the creation of the character Randall Flagg who plays a role in at least nine of King's novels including "The Stand" and other works.
This conversation could obviously span an entire book. But I hope this brief post inspires you to look at horror poetry again and challenge those who think we should let horror poetry wilt by the roadside.