At the end of the gardening season last year I decided to try something a bit different. When it was time to empty the various pots and containers, I saved all the potting soil into a large garbage can. I would shake out the remains of any spent annuals and their roots, leaving behind the 'used' soil (or mixes) in the can. Much to my surprise, I had just about half of a 40 gallon container filled! To that, I added some 'spent' bark mulch, and a few shovels full of good compost and some grass clippings from our final cut. I mixed it all up so all the ingredients were well combined and added a quart of compost tea water. I mixed again, covered it, and left it for the rest of the fall and winter.
Today, I opened the container lid (as I had a few times on warmer days to mix it up a bit) to find wonderful dark soil. I added in 4 cups of bone meal and 2 cups of fish emulsion and gave it a final mix. What I now have is incredibly rich, revitalized potting soil to use in containers this year. There are still 'bits' of decomposing bark in the soil, so it will be light enough to drain well when I water.
By using my soil from last year, I'm saving myself over $100. in new purchases of potting mixes as well as helping the environment by not buying (and disposing of) large plastic bags of dirt!
This 'green' tip is one I will do year after year.