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No-Till Gardening

Soil Structures
In Nature, the earth is not tilled, and fertilizers (dead plants and animals, fallen leaves, etc.) begin as mulches on the soil's surface. Beneath this mulch layer, undisturbed soils develop two distinct features central to the natural interactions between plants and soils. One of these features consists of the soil "horizons" which result from the tendency of the soil to separate into horizontal strata (i.e., mulch, topsoil, and subsoil). The other is a valuable, spongy condition called "crumb structure." Tilling both mixes the soil's horizons and destroys its crumb structure, interfering with the processes and organisms which have evolved to depend upon these features.

Soil Horizons
The soil horizons include the mulch, topsoil, and subsoil layers. The mulch layer consists of plant and animal remains, and is the primary source of the soil's fertility. The topsoil consists of mineral soil, huge numbers of soil organisms, dissolved nutrients, organic matter brought down from the mulch layer, and humus (humus results from the breakdown of organic matter and has an enormous capacity to absorb moisture, hold nutrients, and buffer pH extremes). It is in the topsoil that the majority of the soil's fertility is stored, in the form of soil life and as nutrients held in solution by the soil's humus and clay. The subsoil consists mostly of mineral particles, leached nutrients, and the deeper water- and mineral-seeking plant roots.

Crumb Structure
Crumb structure is a spongy state developed and maintained by the movement of earthworms and plants' roots through the soil. The crumb structure is held together by soil colloids (gel-like substances created by decay organisms), and by earthworms' secretions, used to aid their movement through the soil. Natural crumb structures are quite stable and remain largely intact after rains. The sponginess of the crumb structure is extremely conducive to soil aeration, and to infiltration of water and dissolved nutrients into the soil.

Using Rock Powders to Increase Fertility
Since no-till gardening relies on earthworms to do all the digging (which includes mixing mineral powders into the soil), prior to each mulching a rock-powder mix is applied at the rate of about 4 to 5 pounds per 100 square feet. A good mix consists of roughly equal parts of soft rock phosphate (for slow-release phosphorous), gypsum (for a non-alkaline source of calcium - use lime if your soil is acidic), hardwood ashes (potassium and trace minerals), and bone meal (more phosphorous and calcium). These rock powders will then be slowly and evenly dug in by the worms and the rain as the mulch is consumed.

Tilling and Soil Structure
Tilling mixes organic matter from the mulch layer into the topsoil where is decomposes too quickly for plants to completely utilize (creating a feast-or-famine nutrient cycle) and also mixes mulch materials into the subsoil where they are attacked by anaerobic bacteria (which excrete metabolic byproducts toxic to plant life and soil organisms). Tilling exposes the topsoil's extremely valuable and slowly-forming humus to the air where it can be oxidized and lost, and destroys the soil's existing crumb structure. Tilling decimates the earthworm population, thereby slowing reestablishment of a new crumb structure, and can cause the formation foa hardpan by dislocating fine soil particles and allowing them to be washed downward toward the subsoil where they collect and form a dense sedimentary layer. In short, naturally occurring soil horizons and crumb structures serve vital functions which are interrupted, not aided, by tilling. And since natural patterns always begin to reestablish themselves immediately once disturbed, the gardener who tries to circumvent or override them has to work constantly to prevent their return.

Mulch and Soil Tilth
From these facts it is clear that tilling is an ineffective and at best temporary approach to increasing soil tilth and fertility. Rather than attempting to enforce our own idea of soil tilth on our gardens, we are better advised to cooperate with and use the soil's own natural method for improving fertility - a thick, rich mulch of organic materials to feed soil organisms and plants, which then work toghether to establish natural soil tilth.

Applying Mulches
The most important single strategy in a no-till garden, then, is keeping a thick mulch on the beds at all times to feed the earthworms and the soil. The right proportions are as important for mulches as they would be for compost. The mulch must contain enough grass clippings or other sources of nitrogen to suppoly decomposition microorganisms, or it will temporarily rob the soil of nitrogen (thereby starving plants). Also needed are high-carbon materials like tree leaves, which create humus and keep nitrogenous materials from packing into a mucky layer which would exclude rainwater and air from the soil. By spreading mulches directly on the soil, instead of first converting them to compost, organic materials do double duty - serving as mulch, and as a slow-release organic fertilizer, soil coniditioner, and worm food. Furthermore, the fertilizing value of the materials is more fully utilized, since in a compost pile much of the nitrogen, humus, and minerals are lost through conversion to gases and by rainwater leaching.