It's time to plan for October already. There are many days, weeks and month-long celebrations in October. Halloween is the big deal in October. I have some posts about horror, The Bram Stoker Awards, and why you should not limit horror just to October. I think that what you should consider with your spooky book displays is to be as broad as possible as far as the authors, publishers, and level of scares you have on display. Stephen King is popular and finds his audience without our help so set him aside unless you want to use some of the books he has blurbed and do a display on that. There are roughly 100 so you likely own some of them at your library.
There are also opportunities to take authors like King and come up with read alikes. One of the most common readers advisory questions I get is "What should I read if I've read all of Stephen King and Dean Koontz?" There are lists here, here, here, here, and here. I find Reddit useful for searches like this because you are getting answers from readers. Because King has written so many books, there are many options. For Dean Koontz, try here, here, here, and here.
Hispanic Heritage Month crosses over into October.
Columbus Day / Indigenous Peoples' Day is on October 12. There is plenty of horror written by Indigenous authors if you want to take your spooky theme and go in that direction. I would suggest that you know your community and your library administration. Use that knowledge as a guide for setting up a display. A balance between both themes is always an option. It's also National Indigenous People's Month which could be a separate display.
It's also Italian-American heritage month which is a quick display to set up. You can use fiction, non-fiction, and DVDs in a display.
With October 1 being National Poetry Day in the UK and October 15 in the USA, setting up a poetry display when it is not April is a great idea. While the 800's are sometimes a hard sell, I find that poetry will get checked out if you put it face out and in front of people.
National Cookbook Month is also in October. There are the James Beard award winners but don't forget local cookbooks. If you partner with some local chefs and restaurants, there is an opportunity for programming as well. Do a book talk in a cooking store or a library card sign up outside a local restaurant.
If it all seems overwhelming as you recover from summer reading and prepare for the winter holidays, note the various food related celebrations and put up a display with a sticky note on various titles which notes the celebration day. That can be continuously filled up.
World Space Week is October 4-10. This is a UN designated week to highlight exploration in space. There are tons of fiction, non-fiction, and DVDs in every library that could fill a display for this week. Don't forget children's books. It's fun to echo an adult display with youth materials.
October 14-16 is also Sherlock Holmes weekend in Cape May, New Jersey. How much you focus on the Holmes books would depend on how they circulate in your library. There are also books not written by Doyle which you can find in many collections. Find read-alikes for the Holmes books here, here, and perhaps even books which have won the Agatha Awards.
Finally, I will suggest Punk for a Day Day on October 25. This might be fun and unexpected for your patrons. Beyond whatever is in your non-fiction and DVD collections, try books on these lists:
r/punk: I'm looking for books about punk
r/punk: Any good punk coming of age books to check out?
r/punk: Fictional Punk Rock Literature?
r/booksuggestions: Books with punk characters/culture?
Goodreads: Best Punk Books
Goodreads: Best YA Books With Punk Rock characters
LitHub: Read These If You Aren’t A Poseur: Books That Embody The Punk Ethos
