While this book does not talk about Hoyas per se, it does a fantastic job of helping people who never thought they had a green thumb to develop one. The book is called The New Plant Parent: Develop Your Green Thumb and Care for Your House-Plant Family and it is written by Darryl Cheng. I read it cover to cover and although I have been taking care of plants for over 40 years I still learned a thing or two from it. Anyhow this book gets my highest recommendation, and it would make a great gift for anyone who has the tiniest inclination to want to grow houseplants.