The Humming Room states "A novel inspired by The Secret Garden." I have loved The Secret Garden since I first read it as a young child so I was keen to explore this book by Ellen Potter - I recently read and really enjoyed her book SLOB.
The plot of this book is indeed exactly like The Secret Garden but the setting is quite different and the garden has been inspired by the Amazon rainforest. Roo Fanshaw is sent to live with her reclusive and mysterious Uncle following the death of her father and step mother. Mr Fanshaw lives on an island called Cough Rock in a building that was once a tuberculosis sanitarium for children. Roo is told not to go near the west wing. Of course very soon after her arrival she goes exploring and eventually meets Phillip, Mr Fanshaw's sickly son, and a mysterious island boy called Jack.
I picked up this book from my huge reading pile yesterday intending (as I often do) to read a page or two. Several hours later I lifted my head and let out an enormous sigh of satisfaction. This is an engrossing and enjoyable book perfect for the middle primary reader. I would suggest looking for Journey to the River Sea after you read The Humming Room. Here is a review with a detailed comparison between The Secret Garden and The Humming Room.
Here is scene when Roo first sees the garden :
"The glass dome enclosed what looked like an ancient, brittle jungle. Dead trees towered up out of the dirt floor. Their branches were thin, many broken and hanging, trapped with in the spindly arms of other branches. Thick, ropey vines twisted around the dead trees, climbing up to the very top then tumbling down in thick gray sheets, like grim waterfalls. Clinging to some of the panes on the dome were brown creepers, pressing themselves against the glass as though pleading to be let out. ... It was the saddest and most beautiful place Roo had ever seen"