One imagines that the division between interior and exterior rooms at gardener P. Allen Smith's Arkansas home is so blurred that visitors move freely between them without pause of step or interruption of conversation. And that's just how he likes it. In fact, that's how he'd like all of us to live. A garden designer with a mission, Allen created a series of garden reports in 1998 that aired in the U.S. on local news programs and the Weather Channel. The spots generated a storm of interest, and Allen went on to create his own syndicated 30-minute gardening show, P. Allen Smith Gardens, and website, pallensmith.com, which gets more than three million hits each month. His new show, P. Allen Smith's Garden Home, which began airing on PBS in April, and companion book outline the 12 principles by which the outdoors can be shaped into usable and beautiful spaces. Here, he elaborates on how best to create your own inviting garden rooms.

S@H: Why do you think garden rooms are important?
PAS: They're important because they make it possible for us to live in nature rather than merely pass through it. And from a practical standpoint, the concept of distinct and separate rooms in a garden makes the task of creating and maintaining a garden less daunting. Tackling a huge expanse of space is so overwhelming. People panic and think, "What do I do? Where do I start?" I like to break a space down into smaller, more manageable rooms.

S@H: So where do you start the process of creating garden rooms?
PAS: I start by assessing needs and desires, balancing reality and fantasy. Then, I try to wed those concepts to the look and feel of the house. I take my lead from the inside. The fountain garden at my house is off my study, and the two spaces work so well together. Why? Because the dimensions of the garden room are only slightly larger than those of the study. The study has dark green walls and the "walls" of the garden room are glossy green needlepoint holly.

S@H: What's the biggest mistake people make when creating gardens?
PAS: One mistake that can easily be fixed is the approach [people take] to planting. Often, I see people plant in a meagre, spotty way. They go for a botanical zoo, with one of everything, instead of painting with a wide brush. What we need is abundance, grouping similar plants together to create impact. When I go into someone's garden, I'll often just rearrange the plants—and what a difference that can make! That theory is especially true in small gardens such as balconies or rooftop patios. I'd cluster containers together instead of dotting them around the space. Often, I'll plant three different pots with the same plant or group of plants to achieve a bold, cohesive look.

S@H: In your new book you talk about the importance of enclosure….
PAS: There's a reason "Enclosure" is the first chapter. It's the most important part of a garden: it creates that sense of separate rooms, but it also helps build mystery, and that's so important. We're often given to showing everything we have at first glance. We need to lure a visitor and reveal a garden bit by bit. We want guests to wonder what's beyond that hedge or around that curve. A garden should invite curiosity. I like objects to come over the top of a hedge or wall; you get a glimpse, but you have to go around the corner to really see what's there. Mystery is a handmaiden to surprise, and in a garden we need to have both.

S@H: You also emphasize the importance of whimsy in a garden. What does that mean to you?
PAS: The garden is about beauty and tranquility, but it's also about fun. I had wonderful garden experiences as a child, so I always look for ways to engage children in a garden. Anything that unleashes wonderment, like animal-shape topiaries or plants with peculiar names or forms, is important. I'm always looking for touchstones of that quality. That's true garden magic.