Reddit reviews Making Wild Wines & Meads: 125 Unusual Recipes Using Herbs, Fruits, Flowers & More

The only other one I know of besides Schramm's book is Making Wild Wines and Meads

Better double check on lilac before using it. I have at least one source here that says do not use it, or rhubarb leaves also (not that you were planning on putting them in, but could be toxic). Many times the info you see on flowers doesn't include whether or not it's toxic in food/beverages. I guess there would be some info on this in a herbal encyclopedia or from others who make herbal wines. Just be extra cautious before trying new stuff (as you are, obviously), especially anything that's a flower or fungus (mushrooms, etc).

Schramm's book is definitely at the top some other good reads are:

On Mead:

• Making Mead (honeywine) - Roger A Morse Link
  
• Making mead - Bryan Acton and Peter Duncan Link
  
  WineMaking in general:
  
  
• The art of making wine - Stanley F Anderson and Raymond Hull Link
  
• Country Wines - Pattie Vargas and Rich Gulling Link
  
• Techniques in Home Winemaking - Daniel Pambianchi Link
  
  Good Reads for science:
  
  
• An analysis of brewing techniques - George and Laurie Fix Link
  
• Principles of brewing science - George Fix Link