What makes this book so useful for haiku writers is that the kigo are very often specific to a particular month though they may also be used a bit beyond at times to connect to the broader season depending on the particular words connotations.
The book also provides one or more famous haiku using that particular kigo. The poems are written in Japanese, phonetically in English then with English translation making it an excellent source for haiku writers.
Other kigo in may are Baku shu ya: wheat harvest time, Natsu no tsuki: the summer moon
For May it also has a long description of how in Japan people would change their tatami mats, put on lighter kimono 'koromo gae' and wear colors for May such as light purple and very light pink 'kakitsubata goromo.
Following the Japanse way of tea is about following the seasons and changes in nature. These changes are reflected in changes in the tearoom. They are also reflected in the scroll hung in the tokonoma. Often times the scroll with have a haiku that employs a kigo.
One other websource for kigo is
500 Essential Kigo selected by Kenkichi Yamamoto. Best wishes and happy writing ! MWT.
About the Author
Matthew William Thivierge has abandoned his PhD studies in Shakespeare and is now currently almost half-way through becoming a tea-master (Japanese,Korean & Chinese tea ceremony). He is a part time Ninjologist with some Jagaek studies (Korean 'ninja') and on occasion views the carrying on of pirates from his balcony mounted telescope.