This isn't a book for the cottage gardener or the complacent. It is certain to spark a powerful response in many readers – if it has many readers. Conceptual landscape design is not a subject of widespread interest in most gardening circles, certainly not in North America.

Avant Gardeners may delight you, annoy you, frustrate you, spark new insights about gardening and design. I have to confess my prejudice. I appreciate the work of some conceptual landscape designers. I’ve always liked Martha Schwartz’ playful park at Jacob Javits Plaza (we call it “the Federal Building”) in New York City – liked it years before I even knew it was designed by Martha Schwartz – even before I knew Martha Schwartz existed. But I dislike many of the conceptual landscapes in this book.

Admittedly, some are beautiful, or so appropriate to place, I can’t deny their relevance to the urban world: I’m remembering the first landscape in the book, designed by Atelier Big City, a small, mainly concrete park for hanging out and skateboarding under an elevated bridge approach in Montreal that seems a perfect solution for an almost-waste-space. While most conceptual landscapes are urban, some are not. Wigandia, for example, William Martin’s ecologically appropriate garden-cum-artwork on the side of a volcano in Australia is full of plants that thrive in drought, and it stands as a direct, even polemical, criticism of the prevalence of "British style" gardens so inappropriate to Australia, a land of sun, heat and scarce water resources.

Tim Richardson defines a conceptual garden as a landscape designed using a single overriding concept: "Conceptualist landscapes are predicated on ideas rather than plants or the architectural use of hard materials. Such spaces are underpinned by a single concept, or visual motif, which informs every aspect of the design." Many conceptual gardeners use no plants, some only artificial materials. Others design what appear to be more conventional gardens, with plants and hardscaping, but the design is controlled with strict intellectual discipline.

Mr. Richardson is a very good writer, and an agile and informed thinker about gardens. I come away from Avant Gardeners feeling disturbed, not quite able to see why many of the conceptual landscapes in this book are not more aptly called outdoor conceptual or installation art. Some choices seem to be arbitrary. Perhaps it doesn't matter and Mr. Richardson's point is just to stir things up.

I can't read his intent but, for me, this is the point of the book: to question the very meaning of the word "garden", to push the borders of our understanding of gardens, and to open up new possibilities. Whatever your reaction to this book, it will make you think about what a garden is. And that’s a service to the culture of gardening throughout the world.