So how do you become sustainable outside? Well it goes back to basics: reduce, reuse, recycle.
Reduce is just to consume less. Less human input like fertilizing, gas mowing, and adding weed'n'feed. These things make our yards become addicted to our behavior rather than sustaining themselves. Some say the addiction is like putting our yards on Crack.
Reusing is finding new uses for the things you already have. It's like regifting to yourself. Our yard uses a poorly constructed sidewalk that's been broken to become a drylaid "stone" wall. It's been in place for six years now and doing great.
Recycle for me would include composting. We now take our household organic kitchen waste (peels, seeds, cores, skins) and add them to a compost pile. They in turn become soil for the yard. FREE SOIL!