A Few Thoughts on Organic Gardening - 2. Increasing Humus

Soil Care: Increasing Humus

The successful gardener misses no opportunity to add organic matter to his soil!

Compost

Your soil will gratefully accept and “digest” any amount of compost you have the time, energy, and materials to make. A good compost heap is made by alternating layers of high-carbon materials (leaves, straw, dried plant remains from the garden, etc.) and high-nitrogen materials (fresh green plants, manures, spoiled hay, etc.). Technically, the overall ratio between carbon and nitrogen in the heap should be 30:1. Practically, you learn from experience the correct ratio to use when assembling the pile, based on the materials at hand. Generally, carbon layers will be thicker than nitrogen layers. Do not make either too thick—having multiple thinner layers makes for better dispersion of the base ingredients in the heap. The pile should be watered from time to time during assembly. You want the final heap to be evenly moist, but not sopping wet. Some gardeners add a compost inoculant—a purchased “starter” of live microbes to kick off the fermentation process. While such inoculants certainly “work” in the sense that they actually do introduce live cultures into the heap, you really don’t need to purchase starter cultures. Just sprinkle some finished compost from a previous batch into the mix. Or sprinkle in some good garden soil. Either is teeming with the sorts of microbes that live in and convert a compost heap.

You can make your compost as an open heap, or confine it with pallets tied together, snow fencing, poultry netting, etc.

A properly made heap will heat up in a matter of days. You know that you’ve made a good heap if you stick your hand into the center and cannot hold it there without getting burned—a properly made heap is very hot! Once the heat has peaked, it is a good idea to turn the heap. Yes, making compost—in significant quantities, at any rate—is rather labor intensive.

Please note that compost should be thoroughly decomposed before being used. If you have a coarse, unfinished compost with a great deal of large leaf fragments, say, such a compost will require further breakdown in the soil. The microbes driving that breakdown require nitrogen for their work, and will in effect “rob” the surrounding soil of nitrogen until the decomposition is complete. The result could be decreased plant growth in that bed until the coarse matter is completely broken down, perhaps an entire season. It is much better, if you have a heap that doesn’t break down properly—perhaps because you had too much carbon or too little nitrogen, or because you allowed the heap to dry out—to run it through a new heap rather than use it in its coarse, half-finished state. Well-finished compost will be dark, fine, with little that is recognizable from the starting materials—and will smell like rich, loamy earth from under a mulch.

When ready to use, simply stir compost into the top few inches of the soil. Or add a handful as you set out each started transplant. Compost that needs to be stored should be covered, to keep it moist (and therefore biologically “alive”) and to keep the rain from leaching its nutrients.

Mulches

We might use organic mulches like shredded leaves, straw, etc. to keep the soil cool in summer, protected from frost in early spring and fall, and to keep the soil from drying out. But why is it that we can lay down a heavy mulch in the spring, only to find at the end of the season it has completely disappeared? The interface between the moist underside of a mulch and the surface of the soil is perhaps the most biologically active place in the garden. Throughout the season, the earthworms, soil microbes, and other soil dwellers are feeding on and breaking down the coarse materials of the mulch. The mulch hasn’t disappeared at all by season’s end—it has been converted to humus.

Good mulches include high-carbon materials like shredded leaves and straw. As long as they are on the surface of the soil rather than mixed in with it, they will not “rob” the soil of needed nitrogen for the breakdown of the mulch.

What about grass clippings as mulch? If you are careful with them, you might make them work passably well. I recommend applying a light layer of them at a given time and allowing them to dry out before adding another light layer. A heavy layer of fresh grass clippings quickly mats down into a slimy, molding, putrid mass which tends to block off oxygen exchange to the soil, and is slick and hazardous to walk on.

I much prefer long-stem pasture grasses as a do-it-yourself mulch. In the spring, when the grasses on the pasture are still lush and easily cut, I mow them with a traditional long scythe—one of those hand tools that use the rhythmic interplay of the whole body and are a genuine pleasure to use. After the grass is “laid,” I allow it to dry out for two or three days, then gather it with a hay rake and use it for mulch. Such mulch does not rot and get slimy. It stays springy and pleasant to walk on, stays loose enough for oxygen exchange into the soil, and provides more nutrients to the soil when it breaks down than a high-carbon mulch like straw or leaves.

Cover crops

In contrast to labor-intensive compost, cover crops offer the opportunity to grow your organic matter in place. A cover crop is any crop which is sown to put a close cover over the soil; add biomass to the soil when the plants die or are turned in; prevent the rampant growth of weeds; and, in the case of leguminous plants, fix nitrogen in the soil. Some good candidates for cover crops are:

Grasses: All the grains are easy to use as cover crops—oats, wheat, barley, rye. They establish quickly for a tight cover, are not heavy feeders, and add a lot of biomass. The extensive, matted root systems—especially those of rye—help loosen the soil when the plants die or are turned in: The roots decompose, leaving channels in the soil through which earthworms and rain water move.
Legumes: Clovers, alfalfa, vetches, beans and peas, and other members of the legume group have the ability to fix nitrogen from the air in the form of nitrate nodules attached to their roots. After the plants die, the nodules break down, releasing nitrogen which can be taken up by the feeder roots of plants. Because of the nitrogen fixation, legume cover crops are especially valuable preceding heavy feeders like corn, potatoes, onions, and squash. If you are growing a particular legume in an area for the first time, it is a good idea to inoculate the seeds with a commercial inoculant containing rhizobial bacteria which, in a symbiotic relationship with legume roots, enable them to fix nitrogen in the root nodules. If you have grown that type legume in the same area in the past year or two, it is probably not necessary to inoculate, as the rhizobia bacteria will already be “resident” in the soil.
Other cover crops: Any plant which fulfills the requirements of fast growth and tight cover can be used as a cover crop, regardless of species. For example, buckwheat is a quick cover which can be “popped in” between the harvest of a spring crop and the planting of a fall crop. Also, species that are normally considered food crops can be sown as a cover. For example, members of the crucifer group—mustards, kale, rape, turnips, etc.—can be thickly sown as a cover crop.

A Few Thoughts on Organic Gardening – 2. Increasing Humus

Table of Contents

Soil Care: Increasing Humus

Compost

Mulches

Cover crops