A dash of compost, a dash of used coffee grounds, mix it all up and keep it moist with diluted milk for a few weeks. It should grow some microbes and restore itself.

A potting medium doesn't need microorganisms, it needs a strong and porous physical structure. Most container soils don't last for very long before they collapse, making it more difficult for us to water them properly and more challenging for the plant to have ready access of oxygen at the roots. Used container medium does just fine when tossed out in the garden, or top-dressed over your lawn, however. I wouldn't consider that throwing it away.

Many of us mix our own container medium out of an assortment of products that insure durability and porosity. These would include conifer bark fines, granite grit, Turface (or similar), perlite, and perhaps a smattering of peat. A mix such as this will last longer.

You could improve your existing soil greatly by mixing a large percentage of the above ingredients before re-use this year.

Agree completely.

Al