Symonds wants to DIG the garden, as well as think about it!  Best
resource on that front is work by Anne Yentsch, such as the recent
article with Conrad Goodwin, Karen Metheny, Judd Kratzer, in Historical
Archaeology, her article with Judd in the Naomi Miller and Kathryn
Grayson book, The Archaeology of Garden and Field (with lots of other
nifty articles), and her recent paper with Judd K. for the National
Trust/ICOMOS conference held at Strawberry Hill outside London on the
archaeology of historical gardens.  Recent work by archaeologists at
Colonial Williamsburg is also relevant.  All these projects address the
botanical components of gardens, site formation processess, etc., and are
of much practical use.
 
I'm sending references directly to Jim, but would be happy to recommend
sources to others.  I just haven't gotten nimble enough with this program
to import formatted files like bibliographies!
 
M. Beaudry
Archaeology
Boston U.