The NYT has an article about "gravel gardens" that features the horticulturist at Madison's Olbrich Gardens.

"'I’ve never liked the name, because it just doesn’t conjure the look of what’s possible,' said [Jeff] Epping, the director of horticulture at Olbrich Botanical Gardens, in Madison, Wis., where he created his first gravel garden in 2009, and has planted three more since.... It is precisely because of the gravel that upkeep is so drastically reduced. This is no mere top-dressing — not a mulch layer, but a deliberate foundation four or five inches deep that the garden is planted into. That depth discourages weeds from finding a foothold, while minimizing runoff, directing available water to where roots can use it. Caring for an established gravel garden requires even less attention week to week than taking care of a lawn, which 'might as well be a parking lot, as far as the garden’s creatures go,' Mr. Epping said.... As in a raised bed, what is required is a perimeter barrier — in this case, about six inches high — to contain the gravel at a consistent depth throughout. Otherwise, pebbles near the edges would naturally spread out, and the thinner layer of gravel would invite weeds to self-sow...."

From "Why Gravel Gardens Are Better Than They Sound/Yes, they may require 80 percent less work. But their beauty alone is reason enough to rethink the way you’re gardening now" (NYT).