When you begin to make a garden, it's all too easy to get carried away acquiring plants. One of this, one of that, and suddenly the garden has become a dotty collection of curiosities. One way to avoid this pitfall is to focus on collecting every species of a single plant genus. Like Patrick Anderson; for him, the revered genus was-and remains-Aloe; there are more than 300 species alone. "I do try to select them according to what they will look like in the garden, but I admit that I've never met an aloe I didn't want," says Patrick, a touch ruefully. He echoes the words of every collector who has ever pursued an object of desire down a long and dangerous road that, all too often, ends in a place called Obsession.

Patrick's half-acre garden in Fallbrook, California, in the hills north of San Diego, began innocently enough. More than 20 years ago, he brought home a few specimens from a plant sale at the Huntington Botanical Gardens, where he worked as a volunteer at the plant sales and helped with plant propagation. His efforts soon became concentrated on the Desert Garden area. "I looked at it and thought, I can do that!" he explains, describing how his interest in plants for semi-arid conditions evolved from a childhood love of succulents. "I knew that I wanted to use plants that would be appropriate to the area and also adapted to low water." Unlike many water-wise gardeners, Patrick's preferred watering technique is to use a handheld hose and a simple oscillating sprinkler. He eschews soaker hoses, having determined that they water too narrowly and are a nightmare to maintain.

Today, the main garden area occupies the south-facing slope that rises away from the front of the house. The land was previously devoted to avocado and lime trees, but in 1996, when Patrick decided to get serious about the garden, these were grubbed out and the slope was scraped clean of weeds and unwanted vegetation.

Describing his design technique, he recalls, "There were a couple of trees that I'd planted a few years earlier that we had to work around, but otherwise it was just me observing the ground from various angles to figure out how to shape the garden." Using powdered lime and hoses to mark the way, Patrick devised a meandering path to slow people's pace as they stroll through the garden, thereby encouraging them to look at the plants they pass. Tons of rocks and boulders were brought in to edge the gravel walkways. "It was like arranging furniture, with me directing the guy with the backhoe who was shifting boulders around: 'Put one here, and another here.' It took two days, and by the time they were all in place, I wished I'd gotten three times as many." Never underestimate your need for boulders.