by guest writer Fred Greek

Readily available information suggests that 1,000 sq. ft. minimum of growing area[i] is needed per person. Absent an ongoing and surround healthy ecosystem, fertilizer for your garden area may be limited to home compost, and your human "output".  With a typical modern diet, the upper fertilizing limit for humanure looks to be around 1600 ft. sq., with the limiting nutrient being potassium[ii], and a potential "minimum" area of 600 ft. sq. based on a nitrogen concentration limit.

While a single growing area may be convenient, a number of separate units would permit growing a wider variety of plants in differing conditions, concentrated with other plants needing similar conditions.  It may also be simpler and cheaper to make a series of smaller units than a single 600 to 1,600 sq. ft. "greenhouse" for each person.

Given the space limits of an urban environment, if your garden is on a roof, weight is a major consideration.  Look into the green roof products for ideas in low weight, water proof membrane, drainage layer, etc.  As an approach to “recycling” humanure and urine, look up the Aerobic Pumice Wick presented by Tom Watson.  In short run your black water thru a filter tank to hold solids for aerobic composting, allowing the liquid to drain to the growing bed or storage tank.  In this container you want a lot of wicking material, with a lot of air.  Mr. Watson suggests an 18" bed of pumice in a waterproof base, with a cover of around 6" of soil.   The bottom 1/2" to 1" needs to be water-tight.  Absent pumice, consider coarse sand.   Without a watertight membrane, use the old approach of a layer of straw and manure to help anaerobic bacteria create a water‑impermeable "clogging" layer.

The intent is to create an area to convert the smelly end product of human digestion into a nutrient rich garden bed.  Plant roots access the bed use the nutrients and transpire the water. In the case of too much liquid, the wick acts as a filter and filtered water drains out of the exit pipe.  Ensure the liquid does not rise to the compost level.  Perennial plants are best used in the “sewage” processing area because of their permanent roots, or crops other than root crops.

Overall in your growing area you need to achieve a balance of calorie, vitamin, and palatable crops.  Sweet potatoes growing constantly would take 400 sq. ft. to feed a person.  With edible tubers and leaves, the person would eat 0.5 lb. of cooked leaves and 2.6 lb. of tubers per day.  For optimal yields, an equal amount of sunlight and darkness/day is necessary.

Moringa Olefara[iii] is a small tropical tree that grows to about 25 feet. It has edible tuberous roots, fern-like leaves, and seed pods resembling musician drumsticks.  The pungent horseradish essence is in all parts of the plant, with the roots used as flavoring and in poultices.  It is fast growing and possibly the most nutritious of all leaf crops. The leaves are 7% protein and have extremely high levels of folates, vitamin C, carotenes, calcium, iron, niacin, and other vitamins. The seeds yield an edible and high quality oil earlier used to lubricate fine mechanical swiss watches.  Very tolerate of drought.  Think of it as a vitamin tree which can be grown in an area of 4 to 9 sq. ft.

Man does not live by bread, or calorie crops alone.  The following are per person estimates[iv] of square feet to be planted for a little more variety in "American" crops.  As I add up the space, for each person you are planting around 341 square feet.

Asparagus, 32, Beans, Lima, 4, Beans - Pole,  8, Beans - Bush, 8, Beets, 3, Broccoli, 8, Brussels Sprouts,  11, Cabbage, 13, Cabbage - Chinese 6, Carrots, 3, Cauliflower, 18, Chard - Swiss, 3, Collards & Kale, 10, Eggplant, 9, Lettuce - Head, 17, Lettuce - Leaf, 7, Muskmelon, 7, Mustard, 8, Okra, 10, Onions (plants/sets), 6, Peas, 10, Peppers, 6, Potatoes, Irish, 82, Pumpkins, 8, Radishes, 1, Spinach, 5, Squash - Summer, 9, Squash - Winter, 8, Tomato (stems will sprout roots if buried) 18, Turnip, 3.

So far, the above sample garden requires a little under 800 sq. ft of planting area. To become an "expert" for your area, in the U.S. look up and take your local "Master Gardener" course[v].  For expanded factoids on productive intensive gardening try:

http://sca21.wikia.com/wiki/Mess

[i] One Circle, How to Grow a Complete Diet in Less than 1000 Square Feet, by David Duhon

[ii] Future Fertility, Transforming Human Waste to Human Wealth, by John Beeby

[iii] Re the vitamin benefits of moringa, see www.treesforlife.org

[iv] Arizona Master Gardener Manual

[v] See the American Horticultural Society site http://www.ahs.org/master_gardeners/index.htm