What Weeds Tell Us About Soil

Editor’s note: Weeds are not inherently bad by nature. The informed farmer will know what the presence of various types of weeds means – from compacted to overly wet soil, and more. The late eco-farming expert and Acres U.S.A. founder Charles Walters explains different types of weeds, and the soil conditions and state of soil health that their presence signals.

By Charles Walters


Andre Voisin, the great French farmer and scientist who wrote Soil, Grass and Cancer and Grass Productivity, once declared that most of what he knew came not from the university, but from observing his cows at grass. And so it is with much of what we know about weeds.

Walking the fields with the late C.J. Fenzau in areas as separate as Indiana, Iowa and Idaho, I was able to take note of what weeds were trying to tell us during the early days of the Acres U.S.A. publication. Admittedly, this knowledge has been fleshed out since then. And recent findings build on, rather than tear down, those field observations.

Weeds are an index of what is wrong — and sometimes what is right — with the soil, or at least with the fertility program. In every field on every farm, there are different soil types, and each has a potential for producing certain weeds, depending on how a farmer works the soil. Fall tillage, spring tillage, tillage early or late, if it takes place when the soil is dry or wet, all these things determine the kinds of weeds that will grow that season.

Weeds and Water

As far back as the Dust Bowl days, it became transparently obvious to my Dad — after viewing rainbelt territory near Conway, Missouri — that dryland weeds generally don’t grow in territory that has rain pelting the soil with a steady squall. Thus the presence of salt grass, iron weed, tumbleweed and all the wild sages in soils where flocculation is gone, and wind wafts dust skyward.

There are soil conditions that almost always have restricted amounts of water, and consequently they do not require and cannot grow weeds that thrive when there is plenty of water.

In high rainfall areas of the United States, where irrigation is paper thin and where farmers depend on rainfall for their crop moisture, broadleaf weeds — lambsquarters, pigweed (image below), Jimson weed, buttonweed, and so on — often proliferate.

Weeds and soil – pigweed likes moisture
Green Amaranth, a.k.a., palmer amaranth, careless weed, spleen amaranth, red amaranth, rough pigweed, smooth pigweed, pigweed.

These special conditions appeared classic when C.J. Fenzau and I walked several farms near What Cheer, Iowa, one summer. Where the soil structure was poor and farmers worked the soil under wet conditions, they usually built compaction or set up sedimentary levels in the soil from filtration of silt. This set the stage for a lot of grassy weeds. And in only moments, it seemed, the corn farmer is forced to endure the vicious effects of foxtail and fall panicum.

The soil’s potential might remain. For the season, this pattern of weeds indicates a degenerated soil structure. That’s the signal foxtail and fall panicum send out loud and clear — that there is an imbalanced pH condition in the soil, that tight soil is holding water in excess and refuses to permit it to dry out.

As a consequence, the farmer is always working his soil system on the wet side and creating clods. When he gets done planting fields with clods, they accumulate excess carbon dioxide. Foxtail and fall panicum like carbon dioxide. This triggers certain hormone processes that wake up the foxtail seed and say, It is your turn to live and multiply.

To control the foxtail, it now becomes necessary to change the structure of the soil, and this means tillage, fertility management — not least, pH management, efficient use of water, development of capillary capacity and aeration of the soil. This much accomplished, there is no need for atrazine or other chemicals of organic synthesis.

I recall that in one corn field, planting had been delayed — sure enough, a pattern of rye grass made its stand. Here the crop was planted too long after cultivation. By the time seeds went into the soil, weeds were on the way.

I recall one alfalfa field that had been the victim of poor soil management for seven or eight years. The soil was waterlogged and distressed. And weeds of several types increased and multiplied. It became standard procedure to recommend pH adjustment according to the gospel of Albrecht, and well digested compost. Compost contains its own nitrogen in perfectly available form. It often acts as a precursor of bacteria-fixing nitrogen in the field. Even then it was axiomatic that you never get blue-green algae with N, P, and K.

This business of management, or lack thereof, figured everywhere the Acres U.S.A. pencil and camera went. At one western dairy, it was practice to cut hay and treat it on the spot with an enzyme hormone complex, bio-cultured by Albion Laboratories out of Clearfield, Utah. In a matter of hours, the crop was put up as part of silage or hay bales. Before nightfall the same field got its shot of irrigation water. Weeds rarely got a toehold in such a well managed field, even though herbicides weren’t used.

The Hierarchy of Weeds

Weeds seem to have a pecking order. Once the conditions that permit foxtail and fall panicum are erased, there will be other weeds, but none of them will be as difficult to control or as hazardous to crop production. They have names, both Latin and common. Lambsquarters is one. Pigweed is another. But now the message is different. Both lambsquarter and pigweed say soil conditions are good and fertility is excellent, and there is no reason to come unglued when they appear, for they are as Joe Cocannouer says in Weeds, Guardians of the Soil, a message that the crop will thrive and insects will stay away.

Cocklebur (image below) also indicates that the soil’s phosphate level is good. Lambsquarters, pigweed and cocklebur suggest a trio of superlatives, namely wholesome, highly productive, good quality soils. They are not hard to manage with clean tillage, and do not call for inputs of chemistry from the devil’s pantry.

Cocklebur indicates healthy soil pH level
Common cocklebur tells the farmer that his soil has a high level of vailable phosphate and a reasonable pH level. These high levels of phosphate tend to complex zinc, which activates the cocklebur’s hormone system. Xanthium pennsylvanicum is shown here with its root (A); seedling (B); bur (C); seed (D). One look at cocklebur should tell a farmer not to fertilize with phosphate.

In watching crops grow, other clues have surfaced over the years. There are relatives of grasses that reflect wet soils and wet conditions. Barnyard grass and nut sedge warrant mention. On the other side of the equation, the same soil that produces each of these nemesis can produce ragweed (image below), a dry weather phenomenon. This is particularly true when the crop is one of the small grains. Often the soil tends to dry out as the crop matures. With soil moisture low, bacterial systems do not function too well because, of course, they require water. They do not function to release or convert potassium in a proper form. When the potassium supply from the soil is restricted for whatever reason, or held in a complex form, ragweed reveals itself inside the grain crop. With harvest, contamination in the grain bin becomes apparent.

Ragweed is a sign of poor soil
Carolus Linnaeus called Western ragweed ambrosia psilostachya, thereby exhibiting a wry sense of humor. The illustration exhibits the plant itself; its raceme of male heads and female involucres; the achene or one-seeded fruit; and seeds.

Ragweed (image directly above) tells the farmer that he has poor quality and a wrong form of potassium during the dry part of the crop season. In the cornbelt, when there is too much rain after fall plowing, and in early spring when cold, cloudy weather holds on for a three-week period, then fall-tilled fields still open will generate a whole new crop of bitterweed or smartweed. These arrive under wet soil conditions and grow early in the season. They are related to poorly structured and poorly drained soils. More important, these weeds shout out in understandable terms that something is wrong with the direction of decay of organic matter. Soil that is not in the proper equilibrium will put the decay process into the business of manufacturing alcohols and formaldehyde — in short, embalming fluids.

A good example is often the progenitor for morning glories and other rhizome crops that defy destruction. Picture cattle being fed out on the edge of a field. A lot of waste hay and straw piles up, cemented into place by urine and manure. Two or three years later this mixture is turned under, usually in an effort to return the area back to crop production. The problem is that Jimson weeds and buttonweeds, not crops, will grow. There is a reason for this. They are growing in soils with an excess of organic material that is not decaying properly. A hormone-enzyme process of a different bent takes over. It wakes up weed seeds and allows them to flourish.

The solution is not an overdose of herbicides, but manipulation of pH, distribution of the pileup of organic matter, which in any case must be mulched in more completely. When decay starts to go in the proper direction, Jimson weeds and buttonweeds simply stay dormant and no longer grow in that area. The same principle applies to morning glories and field bindweeds. The last two weeds grow in sick soils, in eroded soils, and in each case they increase and multiply because they are started by an improper decay of organic material.

Sometimes the decay process produces formaldehyde, and at certain stages there is methane, ethane and butane production. These byproducts of decay stimulate the birth of the hormone systems that penetrate ubiquitous weed seeds and tell them to come alive and establish the growth kingdom for that season.

Generally, these processes do not occur throughout the entire field. Almost always, it is a spot here, an eroded hill there, always areas in which something has gone wrong in the past. These are dangerous weeds, and they are very destructive. They climb up plants and drag them down. They short-circuit yields and confer harvest problems on the best of machinery, and often account for farm accidents. Many farmers are maimed for life because they have tried to unplug harvesting equipment, the missing hand or arm a legacy of improper soil management.

Weed Patterns and Crop Performance

There are many factors that have a bearing on weed patterns and crop performance. They’re all interrelated. The ideal is to have pH control, good loamy soil texture, enough decaying organic matter to set the things in motion for better crop and changing weed patterns. These things diminish the frictions of stress and myriads of things that happen.

Every year conditions are different and there has to be different timing. Variables invite changes. There is no way you can machine the process. You can have watergrass come into a waterlogged soil. The next year you waterlog it early and let it dry, and in the early part of the season you get smartweed, a variable of stress reaction.

Different conditions invite a different echelon of life to come in. There is a variable in man — his operating style. I recall a farmer who had everything going perfect. But this year instead of taking a spiketooth rake and dragging it over the corn as it was emerging, the worker assigned the task. By the time he got around to it, the weeds were 3 inches tall. Corn was coming up puny. It was enough to make one shudder. Physical management mistakes can undo everything.

Smartweed can indicate nutritial stress in soil
Smartweed can be an indicator of nutritional stress.

These few observations from the field already suggest that the topic of weeds is a very complex subject. The best weed manual in the world can only hint at solutions to the many problems related to weeds. Unfortunately, those who have taken the weed situation by the nape of the neck and the seat of the pants over the past fifty years have done little more than shake out poisons, not results. Here our objective is to establish a positive viewpoint so that we can analyze what weeds are and accept the Creator’s plan while we appreciate the romance of the tribe.

A Brief Glance at Weed Varieties

There are many mansions in the house of weeds. For example, there are swamp weeds, the cattails and the rushes. There are desert weeds. There are weeds that grow in sand and weeds that grow in silt, and there are weeds that grow in gumbo so tight it resembles modeling clay. Foxtails grow in gumbo, but they also grow in sand when such soils are out of balance and the electrical tension on soil particles is so tight that even sand can build clods and restrict air in the soil enough to set free the hormone process that wakes up foxtail seeds.

There are subsoil weeds. There are weeds that grow in acid conditions and — in the West — there are weeds that like alkaline conditions. Up in Wisconsin and Minnesota there is a weed called “devil’s paint brush” by the locals. This one joins the daisy in having a love affair with sour soils.

Almost always, such soils have an excess of iron and flush out a lot of trace minerals and rock minerals that support the hormone processes that give permission to live for these weed species. It is impossible to grow a high yielding crop when such conditions prevail. It is possible to grow red clover, mammoth clover instead of alfalfa because alfalfa simply won’t have much of a chance as a quality foliage crop.

There are sour soils, neutral soils, alkaline soils and salty soils, and there are weeds that identify with all of these conditions. There are weeds that relate to wet soils and weeds that embrace hot conditions and others that like colder conditions. The degree of sunshine and the length of day and night figure in nature’s equation.

There are weeds that get a head start on the farmer and those that emerge only after the farmer has done his job. All of these weeds have a biography and all seem to share their prophecy with those who look and actually see.

Take rotten weeds, weeds that actually exhibit rotting conditions in the soil. Take stinky weeds and fungal weeds. All reflect the sour, sick, dead excess toxic level of soil components.

There are even herbicide indicator weeds, weeds that grow too well after an accumulation of a certain level of herbicides, usually over several years. Such weeds build up a negative effect on the desirable biological things that have to happen if crop production is to be successful. These weeds tell the United States Department of Agriculture that a measure of madness is afloat when spokesmen make their annual pronouncement that without herbicides and chemicals fifty million U.S. citizens would starve.

There is a damning finality to the evidence that has piled up since Acres U.S.A. began publication twenty-five years ago, because this evidence proves that soils subjected to herbicide use year after year have now achieved a negative depressing effect and gifted degeneration to the soil system, with resultant shortfalls in crop yields. Once such soils are cleansed of herbicide residues, yields can be increased as much as 50 to 75% without the addition of more fertilizer inputs. Moreover, once these soil conditions are corrected, there is a chance to manage the weeds without the use of toxic genetic chemicals.

Every weed, generally within twenty-four to forty-eight hours after germination, has the ability to emit auxins. These are growth factors that come off the seed via rootlets and penetrate out into the soil, sometimes as much as a half-inch from the seed itself. That auxin tells every other species in the immediate neighborhood to stay asleep.

There are hundreds and thousands of seeds in every square foot of soil, and yet only so many germinate and grow each year. They seem to know better than to crowd each other out. Another year, other seeds get their chance. There are enough seed deposits in most soils to last fifty, one hundred, even five hundred years, and some seeds live that long. As long as the chemistry and biology and environmental conditions are there, certain species will wait. The dust storms did not annihilate the tumbleweed seeds or terminate the prickly pear, and all the laws passed to proscribe noxious weeds or prevent seed transport from farm to farm, county to county or state to state are merely so many monuments to the stupidity of man.

Crop Planting and Non-Toxic Weed Management

There is a lesson in all this. As the weed seed germinates, it emits those growth factors. Astute farmers can use weeds to their benefit.

In the spring, when preparing the rootbed, watch the warming and the curing and the ripening and the germinating capacity of the soil system being established. Always, certain weed seeds will start to germinate. The day that you go out and scratch the soil and see germinated weeds with roots about an inch long, that is the time to change the concentration of carbon dioxide and oxygen in the rootbed, and place the desired crop seed.

Within the first twenty-four hours that little weed seed has done its job. It has given off auxins enough to dormatize every other weed seed next to it. It is nature’s form of population control. It just allows certain weed seeds to come alive and stake out a proper domain, meaning space to ensure enough light, air, drainage, ventilation and carbon dioxide to prosper and produce new seed, the Creator’s purpose for a plant.

At the stage of its growth when it germinates, that little weed seed is very susceptible to dying. It can be killed easily simply by taking light tillage equipment through the soil to change the oxygen content. Cation balance, pH, the phosphate level, moisture, air — all determine how long an auxin system will endure in the seedbed. Soils that are completely dead and have no biological capacity, no balance, no equilibrium, soils abused to death with hard chemistry or imbalanced inputs of salt fertilizers, make it possible for the weed crop to hit the ground running, so to speak.

Auxins from weeds can endure in the soil for as long as six to eight weeks. Unfortunately, in most soils managed under the precepts of mainline agriculture, crop auxins can endure only three or four days. That is why partial and imbalanced fertilization usually becomes a sales ticket for insurance spraying, a benchmark for the chemical amateur.

Wild mustard grows best in poorly structured soil
Wild mustard is usually related to a field planted to small grains and the development of slime molds. The weed grows best in areas stressed due to poor drainage and poor structure. Control comes down to applying good compost or nitrogen to get the decay process moving properly. Above, an artist’s conception of  pinnatifida variety (A); the seedling (B); a flower (C); siliques, an elongated fruit divided by a partition between the two carpels in two sections (D); and seeds (E).

Thus the equilibrium established in the soil determines how long growth factors can endure and exercise a dormatizing effect on a crop of weeds. If good biological management gives the crop seed time enough to send out its hormones and say, I command power over this domain for this generation, weeds cease to be the grower’s boogeyman and coffee klatch excuse for bad farming.

No one need accept my word for this. As Rudolf Steiner often said, “Experiment, experiment!’’ Almost every corn grower finds that certain rows were missed or that there are gaps in certain rows. The instant impulse is to replant, sometimes one seed at a time. But it never comes to anything. The new and later plants lack vigor and seem deprived of the potential they ought to have. The reason is simple. The other rows out there have already taken command over that soil domain and do everything they can to shut down the come-lately arrivals. They have sent their hormones out into the soil, and injected a negative effect for the replants to field.

That is why it is necessary when planting any seed crop to control the depth of planting and the spacing of the seed, so that they all come up on equal footing.

Any seed that germinates one or two or four days later than the seed placed next to it never has the potential for producing a high-yielding, field-ripened harvest. Weeds have the most serious effect on crop production during the first week or ten days of their life. That is why a small weed, one only a half inch above the surface of the soil, has such negative effect on the yield and quality of the crop.

C.J. Fenzau, my consultant for An Acres U.S.A. Primer, was so adamant on this point he sometimes repeated it several times in the same conversation. “We must control weeds in the early stages,’’ he would say. “Once the crop is this tall [indicating a foot or more] and a few weeds arrive underneath, they aren’t going to have much of a chance to do a lot of damage.’’

The Bottom Line on Weeds

Across more counties than most people see in a lifetime, this has been the lesson I learned “watching crops grow.’’ You can live with these weeds because they have less effect on yield and quality than when the corn crop is emerging from the soil with weeds arriving at the same time. In theory some of the pre-emergent herbicides set up this condition, but their legacy of damage is worse than the problem they presume to solve.

The bottom line is simply that good soil structure, good soil drainage and good aeration can control biological activity in the soil. In turn, the farmer can increase the nutrient supply and grow a high-yield crop even if a few weeds are supported underneath. But a sick soil with inadequate nutrient release and conversion will have a depressing effect on the yield potential. This allows the weeds to have a more negative effect simply because there are not enough nutrients to feed both the desired crop and the weeds. It also allows weeds to impose water limitations.

Weeds can set up severe competition for water, plant nutrients, air and light. If a crop is dominating and restricting the amount of light, then the light that filters through to the weeds underneath is subdued. Thus the weed is not able to grow as fast as its programmed genetic potential might otherwise allow. Instead of having a fat stemmed plant with a lot of root capacity, it is restricted because it failed to get enough light, and thus becomes a weak, thin-stemmed plant, one with smaller heads.

Any farm reporter who travels from one end of the country to the next can observe how weeds reflect reasonable variables such as altitude, sea level conditions, the amount of light and the angle at which the sun is exposed to that part of the earth. All these things have a bearing on establishing the character and the form and the potential of various weeds. You see some weeds that are short and blocky and thick-stemmed with great leaves, and others that are tall with thin stems and small leaves. These are all reflections of growing conditions. That is why weeds are an indicator of the limitations that exist. Farmers who learn how to read them find that this knowledge confers an ability to make better management decisions on how to live with weeds and still grow a good crop.

Source: Weeds—Control Without Poison