Some Comments on Humus & Its Value in Soil That Date Back Over 40 Years
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

December 25, 2011

Again this week, no specific photos to illustrate this item—not even one of my old buddy ‘Milt’ Carleton! Above: this year’s “last rose of summer (or fall)” which has been in bloom now for about three weeks; followed by the red- and yellow-berried firethorn (Pyracantha) which this year the birds are only now starting to eat—note in upper left you may also see the foregoing rose. Below: a new addition to our garden, Thuja plicata Forever Goldy which is said to hold this colour all winter—we’ll see; and finally a shot of Spencer the standard poodle who is our Christmas guest (actually eight weeks) while a friend, his master, vacations. Author photos.

Recently, while looking up some of what my late friend Dr. R. Milton Carlton had to say about his ‘baby’ 2,4-D for the control of broadleaf weeds, I came across an article of his from the March 1970 issue of GARDEN talk, published by the Chicago Horticultural Society.

I say his ‘baby’ because he considered himself the ‘co-inventor’ of 2,4-D since it was he, when he was director of research for the Vaughan Seed Company in Chicago, who discovered the chemical could be used to kill virtually all broadleaf weeds in turfgrass without harm to the grass itself.

Although I have written quite a bit about ‘Milt’ (as he was affectionately known) and will likely write more about him, this week I want to devote the balance of this article to his advice about humus in soil. Here is what he said back about 41½ years ago.

“Although every living land creature, whether animal or vegetable, is directly or indirectly dependent for life upon soil, all too often we speak of it with contempt. No true soil scientist, however, would be guilty of using such expressions as "Cheap as dirt," or "Common as the dirt under your feet." For to him, soil is an intricate, fascinating substance which contributes most of the nutrient elements upon which the life of Man is completely dependent.

“Far from being a simple mixture of sand, clay and silt, soil is perhaps the most intricate, complex substance with which Man must deal. Take, for example, one element essential to any true soil—humus. Dr. Selman Waksman, discoverer of several life-saving antibiotics, was originally a soil scientist, and wrote a book on humus. It is the most elaborate treatise on the subject in print, some 900 pages in length, yet in the end he must leave unanswered as many questions about its true nature as he answers.

“Mention of humus suggests a question, "What are the elements which differentiate a mixture of clay, sand and silt from true soil?" Certainly, humus is the most important of these—the end-product of the breakdown of organic materials which have accumulated in the mixture. Through the eons that soil has taken to come into existence from granular fragments of sand and gravel eroded from primordial rocks, the original sterile mixture was invaded by roots of plants and by myriad microorganisms. On the death of these living organisms, their decay released nutrients which remained in the soil to feed a new generation of organisms, or were lost down drainage channels, or passed off into the air as carbon dioxide.

“A small fraction of that organic matter was converted into a mysterious substance difficult to analyze or de-scribe, known as humus. It is this fraction which, to a considerable extent, differentiates soil from simple minerals. It has many functions. It serves as a home for microorganisms. It is a slowly-available source of plant food, releasing its nutrients at such a slow rate that a single application of manure, reduced to humus, has been known to continue feeding plants for half a century or more.

“Another function of humus (and other forms of organic matter) is as a buffer against harmful effects of over-doses of fertilizers, pesticides and other harmful agents. It also serves as an absorbing agent, to suck up unused fertilizers and hold it until needed by plant roots. Because of this power to suck up liquids, humus is a valuable agency in holding moisture, particularly so because it is difficult to saturate completely. Thus it can hold both water and air at the same time. Since roots are unable to take up water unless air is also present, the great importance of humus is obvious.

“Its role in nurturing soil organisms has been mentioned. Actually, it is the combinations of these microscopic bits of life with humus which identifies true soil. Dig up a spadeful of rich garden soil and you will hold in that clod of earth as many living organisms including bacteria, fungi, protozoa, rotifers, and others as there are hu-man beings on earth. These tiny bits of life are vital to breaking down plant wastes and dead animal life into elements which plants can use, recycling these so life can go on in the world. Without them, all the world's carbon would be piled up in dead organic matter and life would grind to a halt. They are responsible for many of the functions for which earthworms get credit.

“Most soil scientists insist that true soil cannot exist without presence of one additional element—clay. Like organic matter, clay is a buffering agent, absorbing nutrients and releasing them, often with altered electrical charges. It is only when one attempts to describe the relations between clay and other soil elements that the awesome complexity of soil becomes overwhelming.

“Clay is particularly important in relation to soil solutions—the water-dissolved mineral elements upon which plants feed. The surfaces of almost infinitely-small clay particles (many so small they are even invisible under a microscope) are so extensive that they can adsorb on the outside and absorb on the interfaces enormous amounts of soil solutions. If these surfaces in a cubic foot of soil could be stretched out into a single plane, they would cover several acres.

“Unfortunately, taking soil apart into all these elements does not contribute much to our knowledge of just what it is. It is a living microcosm so complex that disturbing only one element may upset an entire chain. This is one reason why we cannot depend too much on so-called soil analyses to tell us much about them. All an analysis can tell you is what elements are present.

“If you are farming 640 acres of land, this information might save you hundreds of dollars, if it tells you you need less nitrogen, less phosphorus or less potash than you have been applying. In the home garden, however, the amount of fertilizer you might save would be worth less than the soil test would cost.

“It will tell you nothing about the vitality, of soil organisms, the humus content or the many other elements which go into development of a true soil.

“Man is the only animal that manipulates and alters soil to better serve his purposes. As gardeners, we do this more completely and intensively than does the farmer who tills hundreds of acres. What we are striving to create is a highly-developed soil for which the name Gardener's Loam seems appropriate. Into it, we incorporate all the organic matter we can afford, within reason. We fertilize at rates far higher than those used for field crops. We till deeper and water more freely.

“In the end, we produce a rich, mellow substance, Garden Loam, which is one of the most basic elements of gardening. Don't despise it by calling it dirt—treat it with the respect it deserves.” 

  • New Eden
  • Kids Garden
  • Plant a Row Grow a Row