We can’t increase the carbon supply outdoors.  But we can loosen the soil eighteen to twenty-four inches down (or more for deeply-rooting species) in an area as large as the plant’s root system could possibly ramify during its entire growing season.  I’ve seen some GROWers dig holes four feet deep and five feet in diameter for individual plants.  We can use well-finished, strong compost to increase the humus content of that soil, and supplement that with manure tea or liquid fertilizer to provide all the nutrients the plant could possibly use.  We can allocate only one plant to that space and make sure absolutely no competition develops in that space for light, water, or nutrients.  We can keep the soil moist at all times.  By locating the plant against a reflective white wall we can increase its light levels and perhaps the nighttime temperatures (plants make food during the day and use it to grow with at night).

Textural improvements from compost depend greatly on soil type.  Sandy and loamy soils naturally remain open and workable and sustain good tilth with surprisingly small amounts of organic matter.  Two or three hundred pounds (dry weight) of compost per thousand square feet per year will keep coarse-textured soils in wonderful physical condition.  This small amount of humus is also sufficient to encourage the development of a lush soil ecology that creates the natural health of plants.

Silty soils, especially ones with more clay content, tend to become compacted and when low in humus will crust over and puddle when it rains hard.  These may need a little more compost, perhaps in the range of three to five hundred pounds per thousand square feet per year.

Clay soils on the other hand are heavy and airless, easily compacted, hard to work, and hard to keep workable.  The mechanical properties of clay soils greatly benefit from additions of organic matter several times larger than what soils composed of larger particles need.  Given adequate organic matter, even a heavy clay can be made to behave somewhat like a rich loam does.

Perhaps you’ve noticed that I’ve still avoided answering the question, “how good is your compost?” First, lets take a look at laboratory analyses of various kinds of compost, connect that to what they were made from and that to the kind of growing results one might get from them.  I apologize that despite considerable research I was unable to discover more detailed breakdowns from more composting activities.  But the data I do have is sufficient to appreciate the range of possibilities.

Considered as a fertilizer to GROW plants, Municipal Solid Waste (MSW) compost is the lowest grade material I know of.  It is usually broadcast as a surface mulch.  The ingredients municipal composters must process include an indiscriminate mixture of all sorts of urban organic waste:  paper, kitchen garbage, leaves, chipped tree trimmings, commercial organic garbage like restaurant waste, cannery wastes, etc.  Unfortunately, paper comprises the largest single ingredient and it is by nature highly resistant to decomposition.  MSW composting is essentially a recycling process, so no soil, no manure and no special low C/N sources are used to improve the fertilizing value of the finished product.