Perennial Care Manual: A Plant-by-Plant Guide: What to Do & When to Do It by Nancy J. Ondra

This book is really a one-stop shop for just about everything you'd want to know about perennial gardening. In addition to an extensive guide to many specific perennial plants, it includes sections on designing and creating a perennial bed, caring for and maintaining perennials, and transplanting and troubleshooting problems with these long-lived plants. I can tell that this is a book I'll come back to many times.