That lawn is actually a green driveway. For the subbase, we used a special blend of large crushed rock and organic soil. It is weight bearing and has great drainage yet is filled with organic matter and nutrients for the grass. This saves a bunch of water, and I'm pretty sure it hasn't been fertilized yet. We also used a mixture of fescue grasses that are touted as highly drought tolerant, shade tolerant and won't require much fertilizer. It's a seed blend called EcoLawn and so far we are quite happy with it.
After we installed the plastic grass grid for vehicles to drive on, we laid out the stones on the grid, cut out the pattern, then excavated the subbase a few more inches. We added about an inch of 5/8" minus crushed rock, compacted and leveled it to 4" below the top of the grid, then set in the 4" thick pieces of sandstone and packed in around them with sandy soil.
These sandstone pieces, like the sandstone pieces that make up about 1/3 of the nearby stone walls, was reclaimed from the siding of the previous house that was demolished.
Here are several more images of the swirls.

I'd love the idea of a leaf pattern! The concept of the swirls was the idea of the architect, Molly LaPatra.