When I first got into dyeing I heard about this book. It wasn't until I bought it that I finally understood what all the hype is about.
The book is a simple, easy to understand guide of the different dye plants, how to grow them (the part I found really neat is that it tells you how much space each plant needs, and the way it's done is perfect for Square Foot Gardeners like myself) and when and how to harvest them.
In addition to all of this valuable information it shows you the colors that one can expect to get and using a bunch of different fibers and mordants.
If anyone is serious about starting a dye garden, then this book should be at the top of your list.