I am in the process of designing a new patio. I have decided to have 2 foot square concrete pads with 4-6 inch spaces inbetween. Instead of just filling it in with river rock I want to soften the look with plants. Any ideas on low growing plants that can fill in the spaces. I could use grass, but that would require weekly mowing or trimming. I would like something that can last all year long summers here in Palm Springs are pretty harsh. Any suggestions?