A Few Thoughts on Organic Gardening - 1. Soil Care Basics

For those who read “A Few Thoughts on Organic Gardening” before the update of the website, please note that this is a new, expanded version of that article (written in March, 2005 for presentation at a local talk). Even though my gardening practices have changed a bit in the past two years, it still represents a good overview of our approach to gardening. For a more recent overview of the homestead garden, see the sections on the garden year in “Achieving Food Independence on the Modern Homestead”. ~February 2007

Soil Care: Basics

Organic gardening begins with attentive nurture of the soil. Or, as an old truism has it: “Feed the soil, and it will feed you.”

When we grow and harvest crops from our garden soil, we remove some of the fertility that is there. If we do not find ways to replace what we have taken, we are in effect “strip-mining” the soil, robbing it year after year of its native fertility. Sadly, that is what is happening to most of our nation’s best topsoils. In our own backyards, however, we can reverse that trend, taking care to replace what we have removed. Indeed, our goal should be to add more to the soil than we take, so it becomes healthier and more productive every year. The true gardener is the one who finds as much joy in the deepening, darkening, and mellowing of her garden’s soil, as in the crops she harvests from it.

Soil fertility

Since the end of World War Two, there has been a tremendous surge in the use of chemical fertilizers in our nation’s agriculture and indeed, globally. Such fertilizers are highly soluble. Their use assumes that the soil itself is just a prop for the growing plants. The growing of the crops becomes in effect a hydroponic system, with the plant roots fed by nitrogen, phosphorus, and potassium salts (N-P-K) which rapidly go into solution around them with the first rain.

Though the high solubility makes them immediately available to the feeder roots of the plants, these chemical salts are for the same reason leached out of the soil and into groundwater, rivers, lakes, and coastal waters. Not only is much of their potential fertility lost to the plants, but the water in our wells is contaminated; fish die from toxic effects and algal blooms stimulated by excess nutrients in the water; etc. In drier climates, the problem may be that the fertilizer salts to not leach out of the soil enough, with a resulting build-up of salt residues which become more and more toxic to plants. Even in the best of circumstances, these chemical salts have seriously depressing effects on the teeming life in the topsoil-earthworms, microbes, etc.-leading to a steady degrading of the soil season after season.

A major impetus for most organic gardeners is a growing awareness of the whole complex of problems for soil and water which I’ve briefly sketched. However, there is typically an assumption that we must find “organic” equivalents to the chemical fertilizers. In other words, our first inclination is to seek out products we can buy to feed our crops. We have been conditioned to think that soil fertility is a commodity.

The first challenge for the beginning gardener is thus to disabuse himself of that notion: Garden fertility does not come from a bag! To be sure, there may be initial deficiencies in one’s soil that need to be addressed. For example, here in Virginia, our clay soils tend to be rather acidic. Lime is often used to adjust the soil’s pH closer to neutral on the acid/alkaline scale, which most crop species prefer. Also, our soils tend to be deficient in selenium, a mineral needed by animals in only trace amounts, but whose absence can mean serious long-term deficiencies in both livestock and humans. Kelp, the dried meal from a type of seaweed gathered along the coasts of Iceland and Maine, is an excellent soil additive to boost its selenium content. Soils found to be deficient in phosphorus and potassium (actually not too likely here in Virginia) can be amended with colloidal rock phosphate and greensand. Note that these rock powders are slow-release rather than highly soluble: They give up their mineral content slowly and steadily rather than in a single, highly soluble rush. As a result, they do no harm to soil life and do not leach out into groundwater and streams.

Soil tests

I have not had a soil test done by the Extension Service for close to two decades. It may be that they have become a bit more sophisticated in their analyses and recommendations. At the time when I still sent samples to the Extension Service, however, I did not find the results very satisfactory. They seemed to be based strictly on an “N-P-K- mentality”, that is, the analysis concentrated solely on the “big three”: nitrogen, phosphorous, and potassium. No attention was paid to important questions of calcium and magnesium content and the ratio between them, nor to the ratio between calcium and phosphorous, nor to deficiencies of important trace minerals such as boron, selenium, and copper. Most seriously of all, organic matter content was completely ignored, as if it simply had no role to play in the equation.

A further oddity about my results from the Extension Service: Each report invariably found that both phosphorous and potassium were “very high” (again, not surprising in a heavy clay soil), then went on without explanation to recommend a good dosage of N-P-K chemical fertilizer.

I strongly recommend that you start your soil care program with a thorough analysis by a competent soil consultant. I turned to Houston Snoddy, a student of William Albrecht, considered by many one of the greatest soil scientists of the last century. None of the previous soil test reports had prepared me for Mr. Snoddy’s point of view and recommendations. For example, there was no mention of nitrogen. I found that odd, since nitrogen is in the conventional wisdom the key to rapid growth, good size, and abundant harvest. When I asked Mr. Snoddy why there was no recommendation for adding nitrogen, he replied offhandedly, “Oh, you don’t have to worry about nitrogen if your soil organic matter is adequate. Most gardeners would kill for an OM of 6 percent-yours is 8.4 percent. For heavy-feeding crops like corn and squash, you might add a little nitrogen, using blood meal or fish emulsion, otherwise, you don’t need to give it a thought.” “Recommendations for added fertilizer?” “No fertilizer recommended.”

The report was not all good news, however. My dream levels of organic matter were the result of massive applications of compost based on poultry litter over many years. Since chicken manure is high in phosphorus, however, my garden soil’s phosphorous content had climbed to “very high” levels indeed. Far from routinely recommending a standard application of phosphate-containing fertilizers, Mr. Snoddy strongly cautioned me against increasing my garden’s phosphorous levels further. At a certain point, high phosphorous in the soil gets to be “too much of a good thing”, and can have deleterious effects on plants.

Don’t think that Mr. Snoddy was lackadaisical about soil amendments, however. Actually, I had sent him three separate samples: one from my oldest, most developed garden site; one from a new garden site I had been working on for a couple of years; and one from my pasture. The results I mentioned above were with reference to the original garden area. In the site I was in process of developing, he recommended the application of high-calcium limestone. On the pasture area, he recommended the same, plus a trace application of boron.

I ask the reader’s indulgence for having gotten so personally anecdotal about this subject of soil testing. But I have done so to illustrate the importance at the start to have a competent, thorough soil analysis to guide you in addressing some of the soil’s basic needs for adjustment. After that beginning, the techniques discussed below should be sufficient to keep your garden’s soil “in good heart”, as farmers of a bygone era would say, with only an occasional follow-up analysis and minor adjustments needed.

Beyond the initial period of testing and making fundamental, long-term adjustments, soil fertility is not something to buy or dump out of a bag. It is something you grow and nurture. The basic “recipe”: Work to improve soil structure. Work to increase organic matter.

Soil structure

According to the ancient Greeks, the four basic elements are earth, air, fire, and water. We could say that description sums up the composition of soil.

Earth: The basic ingredient of soil is tiny particles of what was once rock, broken down by weather and geologic processes over millions of years. The average size of the particles determines the physical properties of the soil.

Sandy soils are composed of the largest soil particles, with large spaces between them.
Loam soils have medium-sized particles, and also have the good fortune to have accumulated a large amount of humus.
Clay soils have extremely small particles that are very close together.

Air: Plant roots and soil microbes need oxygen as much as we do.
Fire: Humus is the organic residue of what were once plants and animals living on and in the soil. Its further breakdown by soil microbes provides the â€œfireâ€ or energy for the teeming communities of life in the soil, and for uptake by plant roots.
Water: All forms of life require water. How well a soil accepts and retains water in the form of rain determines how well it will grow crops.

Of course, when we gardeners read about the three most common soil types, we all wish we were blessed with a dark, mellow, friable loam in which to grow our crops. We can see the disadvantages of sand-water passes through it easily, so it dries out sooner; there is so much oxygen in it the humus “burns” at a high rate, but surely, we think, clay is the worst of the alternatives. We are, however, pretty much stuck with the basic particle size of the soil we’re working with, and thus with its physical properties. Since we in Virginia are stuck with heavy clay soils, I will concentrate on working with them.

It is easy to conclude that clay soil is a curse. When it rains, it becomes too sticky to work. When it doesn’t, it dries into brick. When we transplant into it, we have to tuck the soil around our carefully nurtured “baby” with exacting care to keep the soil from compacting around its roots. When we direct sow, a crust forms over the surface with the first rain, through which fragile seedlings force their way with difficulty, if at all. Why couldn’t we have been blessed with loam soil instead?

Actually, we can be. Remember, an important component of loam soil is its high humus content. By increasing the humus in our clay soil, we end with a soil much closer to a loam in its physical properties.

Clay actually has high levels of fertility, the highest of all the common soil types, in fact. The challenge is to tap that fertility while changing the physical properties which make clay soil so difficult to work with. There are two additions which initiate these changes.

Lime

As said above, lime is often used to change the pH or acid/alkaline balance in the soil. A further advantage of liming clay soil, however, is that it causes the soil to flocculate. That is, through changes in the electrical charge of the tiny clay particles, lime causes them to clump together into bigger units, in effect creating a soil of larger particle size. The result is an increase in size of the spaces between the clumps, an opening up of the soil structure.

Humus

There is nothing you can do to better improve your garden, whatever your soil type, than increase its humus content! As a technical matter, there is a distinction between organic matter and humus. Consider compost as an example of organic matter. When you look closely at a handful, you see a heap of fragments. Some you might even recognize as bits of leaf or fragments of straw, etc., some might show as an undefinable particle, but you see them as discrete bits. When such organic matter has been completely broken down by the soil life, however, it no longer shows as visible particles. Soil with increasing humus looks darker and is more crumbly, but no longer shows the organic matter as discrete particles. But we need not be concerned about this technical distinction, for practical purposes, we can say that, the more organic matter we add from all sources, the more humus will be produced over time.

I have already referred above to the role of humus as “fuel” for the metabolism of soil microbes. Humus also intermixes with clay particles in the soil, making them less likely to stick together when wet. It also acts like a sponge in the soil, absorbing rainwater when it falls, so the water doesn’t simply pass on through the topsoil, and keeping it available to plants in the root zone.

A Few Thoughts on Organic Gardening – 1. Soil Care Basics