The least expensive solution is to break up the concrete slab and re-lay it on sand with a dirt/sand mixture between the pieces of concrete to create a flagstone-like patio with drainage and ground cover between the "stones."
Also available are locally made permeable pavers that are designed to be laid loose over a sand base. There are local contractors who specialize in laying concrete paving stones.
Hardy, drought-tolerant ground covers such as sedum, thyme, or dymonia might do well in your area. Check with the Theodore Payne Foundation for Wildflowers and Native Plants for this application.
If you prefer a more consistent base on which to do your entertaining, consider using pervious concrete. This material uses the same basic materials as regular concrete, but it has a larger-sized aggregate so that the water drains through it. Creating a permeable surface not only reduces pollutants in the waterways, but also reduces the heat sink caused by large expanses of traditional concrete.
Each of these choices comes with a specific aesthetic.
- If you want a very natural look, the "flagstone" approach is going to be the best.
- You can use concrete stains to make your old concrete look natural. I do not recommend using natural stone, because it isn't a renewable resource.
- Concrete permeable pavers will give you an orderly aesthetic, because you can easily lay out grids and patterns. Because this material is more expensive than salvaged concrete, you can get creative and mix the two.
- Pervious concrete could also be used with the pavers to create patterns and designs.
With all hardscapes, it is extremely important to build a good base of gravel and sand, and be sure it drains properly. The specifics of this vary from place to place due to soil type and code requirements.
For more information:
Theodore Payne Foundation for Wildflowers & Native Plants
Interlocking Concrete Pavement Institute
National Ready Mixed Concrete Association's facts about pervious concrete pavement
The Concrete Manufacturers Association's list of publications on concrete block paving