Gilbert, Richard. The Disjunctive Dragonfly: A New Approach to English-Language Haiku. Updated ed. Winchester, VA: Red Moon Press, 2016.
I recently had this book recommended to me by someone who is also interested in writing nontraditional haiku.
Rotella, Alexis. Milkweed: Selected Haiku & Senryu. Taylorville, IL: Brooks Books, 2024.
Rotella has been one of my favorite haiku poets since I got into the genre, so I was quite excited to hear about the publication of this collection.