From Journey to Forever (https://buff.ly/2IZ9GW8):
"Vegetables are grown in drainless containers ideally with 18 to 20 liters capacity -- stuffed with deciduous tree leaves or grass clippings up to 4/5ths of their capacity, topped by a three to five centimeter layer of good soil, where seeds are planted, or seedlings are transplanted. On the wall of the container, five to ten centimeters from the bottom, a hole is bored for drainage the container thus maintains a water reservoir at the bottom. Finally, a stick is inserted right down to the bottom, that is used to measure the containers' humidity as you would the oil in a car. A container thus prepared, weighs far less than one filled with regular soil."
Organic food production in the slums of Mexico City https://buff.ly/2IZ9GW8