Posted: 30/04/2012 at 17:05
I don't think you'll find one book that will do it all in sufficient detail. I have the RHS Encyclopedia as well as their Dictionary of Plants and Flowers, which is my favourite book for ornamental plants, But for the edibles I turn most often to the Hessayon "Vegetables and Herb Expert" and "Fruit Expert", which are cheap, reliable and easy to use. I even have a spare copy of the fruit and veg one, which I keep in the shed. I also like the Readers' Digest "Food From Your Garden" which includes sections on preparing and preserving fruit and veg.
Second-hand books are fine but make sure they're relatively modern. Old books won't include the best new plants, varieties and materials, and may recommend the use of chemicals that are now banned and unavailable.