Senior librarian Rhian Isaac discovered the book while cross-referencing the library's collection against a global database of known toxic texts.
She said tests would be carried out to assess how much arsenic it contained.
The Poison Book Project - which is the work of Dr Melissa Tedone and Dr Rosie Grayburn at Winterthur Museum, Garden and Library in the US - aims to identify different editions of historic books produced using hazardous compounds and heavy metals such as arsenic.
"This project is really important as it helps librarians across the world work together and understand how and when these books were made as well as what steps we can take to keep track of them and make sure they are safely stored and cared for," Ms Isaac said.
"Amazingly, heavy metals were once quite commonly used in the production of books as a way to achieve what was considered a very aesthetically pleasing shade of green.
"Whilst people at the time were certainly aware substances like arsenic were harmful, they probably didn't understand the many different ways they could be accidentally ingested," she added.
An inscription in the book, which contains tips for budding young gardeners, shows it was gifted to Caroline Gott by her father William in 1855.
Both were descendants of wool merchant Benjamin Gott, who once owned Armley Mills and whose family remained prominent local industrialists for several generations.
"The fact that this particular book also once belonged to the Gott family means its story is also a part of Leeds's history and, with some careful handling and storage, can continue to be part of our collection for many years to come," Ms Isaac said.