Lyn, skimming through your thread here, I wondered if anyone has mentioned the value of amending the soil with organic material before you put down the mulch? The cellulose fibers of all plant material act like little sponges that absorb and hold moisture and nutrients. If you're not already composting, make new beds a year ahead by digging in the shredded leaves, pine needles and stuff, and let them break down for a year before you plant there.
Here in FL we have sand that drains too fast, and all we do is add compost + + + to incorporate those absorbent fibers between the sand particles. Our County landfill makes great compost that is free, so we're lucky. Mulching over an amended bed will hold a LOT more moisture. Wood chip mulch is preferred, and readily available here, but we do not have your fire issues. It breaks down and adds more compost to the soil quickly because of all the hot, wet weather we get in the summer.
I wouldn't use gravel for mulch ever! It retains heat if it's in the sun, sinks into the soil, (unless you put landscape fabric under it) not adding anything useful as it goes, and doesn't retain any moisture. Here in FL we have hot, dry weather in the spring and fall, and the only plants that grow in rock mulched beds are desert plants. If that's what you want to grow, maybe it would work. I have gravel pathways and driveways, and not much of anything grows in them. Recycled rubber is just about as bad, plus it stinks when it gets hot.
