Volume 21, Issue 3, August 2011, of The Literature Base is worth a look! Half the journal is given over to Gardens & Gardening - a unit of work by Kevin Steinberger.
Gardens as Setting, Gardens in Fantasy, The Science of Gardens, Gardens in Other Cultures and Cross-Curriculum Activities. There is a selection of Gardening-Themed Books and a Reference list of books and websites. The Learning Exchange has a copy of this issue and some schools already subscribe to the journal.