Anonymous wrote:If you really are looking for the cheapest option, use free compost and mulch.
In DC: at Fort Totten
http://dpw.dc.gov/service/fort-totten-transfer-station The guard at the gate will direct you to the correct container. Bring your own shovel and containers.
In Greenbelt: at Northway Field, 8108 Northway Road. Drive around to the back of the ball field, on the left.
You could buy some vermiculite and peat moss to add to it, if you want to spend some money. Look on Craigslist to see if any local farmers are advertising compost, top soil, soil, square foot gardening mix, peat moss, vermiculite. I've gotten free compost off of Craigslist from local sheep farmers.