coco-coir is a great product as a soilless seed-starter / potting soil although it tends to be rather expensive. Your average brick costs about $2.00 - when ordered in bulk - and only hydrates up to about 3.5 gallons which is about 0.5 cubic feet.

Of course we're talking much and not soils so I'm not thinking it'd be along the same lines, but you're desired plants (and weeds) would jump up and, likely, love you for it. In terms of nutritional value and water retention it's the tops...even moreso than peat moss.

Speaking of peat-moss, random trivia I learned recently - peat moss is classified as a non-renewable fossil fuel. Under geological compression and a couple hundred thousand years, peat moss is converted into coal. :shrug: