Dig out a small amount of the sand and put planting mix in there for the starting plants.

As the plants spread, they will trap dust and make their own dirt, and they can easily go through the gravel into the dirt under it.

I have a walking path thru a portion of my back yard which resembles your patio. In theory it all makes sense, but the weeds haven't been told they're not supposed to be there. My visual was a walk thru a Forrest with moss, baby's tears, or any other tiny plant that wanted to poke it's head thru the soil, but I didn't expect quite so many weeds.

I'll be cementing my stones in. ;o)