We're planning to use gravel in a large section of our garden instead of mulch. Have seen it can look effective surrounded by drought-tolerant plants like succulents and should reduce/elimate the need to water. But a friend has warned me that gravel retains rather than reflects heat and can bake the roots of any plants you might have. For those that already have gravel gardens, have you found it difficult to keep your plants alive? Has it reduced your water bill?
Gravel will reflect heat, and retain heat after the sun has gone, so any plants in the area might get stressed. You also need to remember that gravel will make its way into the soil. But there are plenty of plants that can thrive in such an environment. You just need to choose carefully.
An alternative to both gravel and mulch might be a fast-growing ground cover.
I prefer to enhance the soil over time with mulch. Certainly saves a lot of water. But it does need regular topping up.
We have used a rainbow stone in a small area of our garden but this is predominately filled with succulents and it is in shade most of the time. Everything has grown really well. We did use a geo fabric underlay so the stones sit on top of the soil. A nice thick mulch is the way to go in a full sun situation.