In addition to Dalley's book, I would recommend Deena Ragavan's work. I attended a symposium at which she presented a rather interesting analysis of temples in Sumerian literature. It is rife with analogies to the natural world, references to water, and mentions of trees within temples. She doesn't confirm the existence of the Hanging Gardens as we would imagine it, but shows a lot of ways in which temples were referenced with many of the terms we would use for a garden.

I unfortunately can't find any of her publications beyond this online.

I had suggested this book in a previous question. The researcher suggests that if the gardens were real they may have been in Nineveh rather than Babylon. I still need to read the book myself, but there was a previous question in which other users seem to agree that it may have been in Nineveh as this researcher suggested.