You can make a compost bin with hardware cloth (actually fine wire mesh. It works great because air can circulate. The question is not how many bins do you need for your garden, but how much compostable materials do you have to fill them? Composting is most efficient when the pile is one cubic yard.

I made raised beds almost just like yours. Some plants will need more than one square, so don't nail down the grids, just lay them in place.

The box in the photo is smaller because it was scaled down for children. Yes, it's on asphalt!

Check out the UCCE Orange County Master Gardener Website for videos on composting.

Easy compost bin

My Square Foot Garden

Composting II