From the Victory Garden.
1 part portland cement
1 part horticultural vermiculate
1 part peat moss
Wear chemical gloves. Mix everything well using a trowel, adding enough water to make a sticky mess. Pack handfuls around the edge of the mold. Punch a drainage hole in the bottom, flatten the bottom so it doesn’t roll away, cover with plastic, and place in the shade for two days. Remove from mold and scrub with a wire brush for texture. Place in the sun to finish drying. Leave the containers outside in the rain for a year before planting anything in it. The cement mixture is extremely alkaline and will likely kill anything planted in it before the lime leaches away.