The “Lowdown” on Lowdown Chemical Fertilizers

A reader recently wrote in asking:

… I have always taken pride in my lawn. Attaining “the perfect lawn” has long been a goal and kind of hobby of mine. I keep a consistent and thorough lawn maintenance routine. I am careful to mow at the recommended height and so on, water three times a week, thatch & aerate regularly, over-seed every year, minimize any & all kind of heavy traffic. I’ve been using the same big brand name lawn fertilizers & weed killers, religiously, for years now and they have always seemed to be working fine.

But over the past few years, especially, the lawn just seems to all be coming unravelled. I noticed it starting to decline a bit more with each year. Particularly, certain parts of the yard, at first, seemed to be looking a little thinner and patchy, but now it just seems to be crashing, altogether. Weeds and infestations of all kinds popping up everywhere. The only parts of the lawn that doesn’t look dead are the parts that are moss. I’ve even stepped up my fertilizing/weed & moss killing routine (within manufacturer recommended limits) but, alas, nothing.

Everything I had been doing for years seemed to be working fine and nothing changed in the routine. What could be causing all this??

~Bob W. (Seattle, WA)

Thanks for your message, Bob!

Based on this information (and other small clues in your message) and name of the fertilizers, etc. (here, omitted) being used, my SHORT ANSWER is: “most likely, CHEMICAL FERTILIZERS”.

The LONG ANSWER involves a much larger discussion of, not just grass, but soil, soil biology, soil pH, the differences between chemical and organic fertilizers, and a whole bunch more. None of which are a short topic, in themselves. So my goal with this article is to help break it down to the bare essentials of these significantly relevant, aforementioned subjects, enough to where you, the reader, have a stronger working knowledge and tools for diagnosing and treating, lawn & garden issues, building stronger, more sustainable gardens, as well as understanding your options (and impacts) and more.

So to better situate the case for why chemical fertilizers are likely the problem and not a solution, let’s start with 1.) a brief description of some of the main “cast of characters”, with regards to micro and macro-organisms such as beneficial fungi, bacteria, etc. that are key components of soil life, soil structure, health and fertility. Then we will go on to discuss 2.) main ingredients found in chemical lawn fertilizers, what they do and don’t do and how they are designed to function and there impact on soil ecosystems. 3.) facts about grass itself, moss and common weeds and what they can tell us about our soil conditions. 4.) I will also touch on a couple relevant composting basics. The reason being that, in order to better explain how chemical fertilizers effect soil structure, health and fertility, it is essential to first understand a bit about how the above mentioned (organic) components work together to create a fully self-sustaining, self-regulating cycling system that IS your soil.

Soil biology itself is comprised of a highly complex network of interconnected bacteria, fungi, actinomycetes and other micro and macro-fauna that are directly responsible for the creation, sustainability and fertility of soil. The reason for covering this is to provide an explicit explanation of what chemical fertilizers are doing to your lawn and soil, what they do not do and how they are connected to specific lawn problems and other side effects. Another reason for getting into soil biology is that it offers explanations into how, even when starting with “same soil, same seed, same fertilizer” factors, as you indicated in your message, completely different lawn conditions/symptoms, such as moss in shaded areas of the yard and dead patches and/or weeds in other parts of the yard with different sun exposures, etc., can emerge.

Also, it should be understood that the role of each of these organisms are requisite to soil capable of successfully sustaining plant life and that, collectively, they are also each part of a “food chain cycle” that maintains a healthy balance among each population. Anything that negatively impacts any one of these populations, thus throwing off this delicate balance, sets off a whole chain reaction of other consequences such as disease, infestations, etc.


To better explain their role in the production of well structured, fertile soil, it’s best to start with the chicken and backtrack to the egg, so to speak, and discuss some composting basics. The most efficient way to produce high quality, healthy compost is by layering, in multiple equal portions, nitrogen sources (ex. grass clippings, leaves, etc.) and carbon sources (ex. twigs, bark and other woody debris, etc.) in a location with good drainage, sufficient but not excessive airflow, sun exposure or moisture.

The “chemical reaction” that ensues as a result, breaking these materials down and converting it into nutrient rich soil, in a form that can be accessed and used by plants, is begun with the introduction of three different bacteria that enter the compost pile, (in consecutive order of appearance) the Psychrophilic, Mesophilic and Thermophilic bacteria. They are the first to begin the breaking down of these materials in your compost pile. The “nitrogen” sources are utilized by the bacteria to build protein in their bodies, to grow and reproduce, while “carbon” sources provide them the energy to keep “eating” (decomposing the pile). In the process, their activity progressively raises the temperature of the compost pile up to 140F (the ideal temperature for killing off most disease in soil as well as killing off most weed seeds) and as high as + 160F (which, too hot, can render your soil effectively sterile and loose it’s disease fighting properties).

Next are the Actinomycetes, that possess characteristics common to both bacteria and fungi. They are the grayish-white fuzz you see in fresh compost. They are also the source of the dark color and “earthy” smell of nutrient rich soil. They play an important role in the decomposing of more resistant organic materials, such as cellulose, starches, proteins, polysaccharides, chitin, etc. As they do, they are replenishing the soil carbon, nitrogen, ammonia and other essential plant nutrients. In the process, they are also responsible for producing antibiotics that help in fending off several different diseases affecting plant roots.

Also playing an important role in the breaking down of organic matter and the cycling of nutrients are a wide variety of fungi species, from thread-like colonies, single celled yeasts, mushrooms, etc. One such important fungi that you may have seen listed as a “feature special ingredient” in organic soil amendments/conditioners and other ”specialty soils” are the Mycorrhizal fungi. When you pull a plant up by the roots, the dense network fine white branch-like root structures binding large clumps of soil to the plant’s roots are actually the Mycorrhizal fungi. They form a symbiotic relationship with plants, which provide carbohydrates to the fungi, who in return expand the reach of plant roots to gather water and nutrients such as phosphorus, zinc, while also making plants more drought and disease resistant, and more resilient to soil salinity, contaminants, etc.

In addition, we have protozoa, nematodes and a whole range of other micro-invertebrate, microfauna and macro-fauna, earthworms, ants, beetles, etc. Each, individually and uniquely, play an important role in the production and maintenance of healthy, well structured, nutrient rich soil. For our purposes here, I will leave much of that for another discussion, other than to say that chemical fertilizers are also directly responsible for the decline, killing off of and/or otherwise compromising the highly complex, intricate and delicate balance among these important players in your soil.


1.) NITROGEN:   Nitrogen aids in the production of chlorophyll (an essential chemical for photosynthesis) which promotes healthy green leaf growth. Nitrogen is the most important and most absorbed nutrient than any other. It is also an important building block of proteins, nucleic acids, etc. The primary source of nitrogen for soil actually comes from atmospheric deposition and biological nitrogen fixation. In short, plant friendly bacteria take nitrogen in the atmosphere and convert it into a form that plants can access. This is one of a number of reasons why lawns, for example, tend to struggle a bit more in enclosed areas with reduced and stagnant airflow. Another source of nitrogen in soil is from decomposing plants, leaves, grass clippings, etc. Nitrogen shares a special connection with the next nutrient we will be looking at, Phosphorus, in that nitrogen, as previously noted, enables plants to store solar energy, while phosphorus facilitates the usage of said energy.

2.) PHOSPHORUS:   Phosphorus promotes healthy root, flower, seed/fruit development, energy storage, conversion of solar energy into useful compounds, cell division and the development of new tissue by helping convert other nutrients into usable building blocks essential to plant’s growth process. Phosphorus is present in soil in two distinct forms, 1.) organic (decomposed plant material, urine, manure, bone ash, etc.) and mineral form. Where mineral forms of phosphorus are concerned, soil pH has a determining effect on the kinds of phosphorus compounds present in the soil. In acidic soils with low pH levels , phosphorus will fixate with aluminum, manganese and iron. In alkaline soils with high pH levels, phosphorus primarily fixates with calcium. Maximum availability of phosphorus occurs in neutral soils with a pH of 6 to 7. Comparatively, soils with a higher contents of organic matter contain over 50% total phosphorus content over the 3% available in soils with low organic content. Another reason to mulch regularly! Especially if you routinely clean up leaves, grass clippings, dead plant material, etc from your lawn and garden beds. Over saturation of phosphorus has the effect of hardening soils, which diminishes the oxygen levels necessary for plant roots to be able to access phosphorus in the soil. The same is true of frequently water logged soils with poor drainage. Cooler soil temperatures also diminishes most plant’s ability to absorb phosphorus.

3.) POTASSIUM:   Potassium is of the Alkali Metals element category, found in many minerals. Potassium promotes healthy root and stem growth, helps plants become more disease, drought, cold damage, stress resistant by promoting stronger and thicker cell walls, and aids in the cellular processes involved in photosynthesis, nutrient absorption, the production of proteins, enzyme activity, water absorption and respiration. The rate at which potassium is released into the soil is influenced by environmental factors within and acting upon the soil, like soil structure, pH levels, temperature, drainage, wetting and drying patterns/rates as well as macro-fauna activity. For example, potassium is less available in dry soil, while in wet soil with poor drainage reduces aeration, and thus plant’s ability to absorb potassium.

CHEMICAL FERTILIZERS: “A patient cured is a customer lost”

Here’s how it all comes together, in terms of the effects of prolonged use of chemical fertilizers. Chemical fertilizers are essentially salts. Think “bath salts”. Certain specific elements (essential oils, etc.) are extracted from it’s organic form (say lavender, rose petals, etc.) and converted into a concentrated solid form (”salts/crystals”, etc.) that completely dissolves in water to release their fragrance and what-not. That is basically how chemical fertilizers are conceived and designed, often derived from by-products of the production and refinement of petroleum products.

Herein lies the insidious nature of chemical fertilizers. Only about 30% of chemical fertilizers actually reach plant roots. The rest leaches right through the soil (which leads to significant groundwater contamination, greenhouse gas pollution). By completely excluding organic matter from the equation, (to begin with) you are eliminating the very medium that provides for the accumulation, production, conversion, transfer and storage of said nutrients, as well as starving the central component underlying an entire (self-regulating and self-sustaining) soil ecosystem required for sustaining plant life altogether. In fact, chemical fertilizers have the effect of overstimulating microorganism activity devouring up existing organic matter in the soil, beyond a sustainable rate, thus ultimately leading to significant nutrient depletion, consequent beneficial microbe decline and death, soil infertility, etc.

Over time, this creates a direct dependency on yet even progressively more chemical applications to sustain the same lawn, as the only other option for plants to acquire vital nutrients, etc. has been critically and effectively compromised as a result. While this may be great for profits, it’s a one-way road to soil collapse. Chemical fertilizers contribute absolutely nothing to actual soil structure and fertility. Not to mention, prolonged use results in the build-up of arsenic, uranium, cadmium and other such toxic chemicals, in your soil.

To be sure, chemical fertilizers deliver the instant gratification quick fix many folks are looking for. At first. And until they don’t anymore, no matter how much chemicals you put down. Here’s how it works. Due to the very vehicle that makes that quick fix possible (water-soluble salts designed for instant absorption), prolonged regular use leads to a cumulative over-saturation and acidification of your soil. Chemical nitrogen, for example, will significantly lower soil pH (acidic).

Also, Soil pH (or “potential hydrogen”) refers to the measure of acidity or alkalinity of a soil. Soil pH is charted on a scale between #1 (most acidic) to #14 (most alkaline), with #7 being neutral. Apart from certain plants, for example hydrangeas, rhoddies and blueberries, that (in this case) prefer a slightly more acidic soil, most plants prefer a neutral leaning pH between 5.5 and 7.5, that offers better conditions by which more essential nutrients are made available to plants (nitrogen, magnesium, potassium, sulfur, phosphorus, calcium, etc.).

Grass prefers a pH of 6.5 – 7.0 pH. Moss, on the other hand, prefers acidic soils of 5.5 pH or lower. Chemical moss killers are another product to be avoided as they ultimately exasperate the level of soil acidification that moss likes. Moss spreads by spores and so there is really no way to eliminate moss from your lawn without improving soil pH and structure to something more favorable to grass and thus, less favorable to moss growth. Moss is not competing with and/or overtaking your lawn. Instead, it offers an explicit map of all the low fertility, acidic, poor soil structure problem areas in your lawn. Shaded areas with diminished airflow, for example, add an additional, overlapping layer of favorable conditions for moss growth. Offering a meaningful solution to moss in your lawn often requires a combination of improving both soil conditions as well as environmental conditions. That said, in the meantime, moss is actually mending and contributing something to overall soil health and stability, keeps weeds out, grows where grass won’t and is full and green year round.

Phosphorus does not dissolve in water. As previously stated, overuse will cause the soil to harden and thus prevent sufficient root, water and air penetration to sustain grass. Also, soils high in organic matter can contribute 50% of the available phosphorus. There are many factors, including soil ph, structure, amount of organic matter present, etc. to temperature, sun exposure, moisture, amount and type of phosphorus applied, that directly impact the form of phosphorus found in soil, that directly bears on plants’ ability to access and make use of it. Phosphorus is most available within 6.0 – 7.0 pH. The higher the soil pH (alkaline) the less phosphorus is available. The absorption of phosphorus is diminished by compacted and water-logged clay soil, reduced soil respiration and lower soil temperatures. Apart from soil temperature, prolonged use of chemical fertilizers are a direct contributor to these soil conditions.

Another example is the third essential nutrient found in lawn fertilizers, Potassium. Over-saturation of potassium hardens topsoil in areas of higher direct sun exposure areas, yielding higher soil temperatures. As this occurs, potassium becomes less available to plants. Similarly, in cool, water-logged soil with poor drainage, soil aeration is reduced, thus reducing plant’s ability to absorb potassium. These kinds of conditions also have the effect of slowing the rate of chemical reactions responsible for making potassium available in a form that can be used by plants. As well, it should be understood that, with regard to soil biology, anything that directly impacts any one bacteria, fungi, micro or macro organisms population, has an effect on all the rest of the chain, that leads to disease, infestations, etc.

Apart from the effects of prolonged use of chemical fertilizers on soil micro and macro organisms, there are a number of physical factors that have a direct impact on said organisms’ health, population, activity. Those being sun exposure, soil pH level, soil temperature, moisture level, soil mineralogy and soil respiration. In combination with the effects of chemicals, they have an amplifying effect.

How this relates to your lawn is in how certain such conditions often manifest in specific kinds of symptoms, even when starting with “same seed, same soil, etc.”. For example, 1.) microorganism activity will decline with increasingly higher and lower temperatures, thus resulting in diminished soil health, fertility and poor soil structure. 2.) acidic soils can have the effect of increasing solubility of certain elements that can be toxic to micro and macro fauna at certain levels. Also earthworms, for example can’t tolerate highly acidic soils, thus resulting in the loss of an important player in terms of soil fertility, soil structure and respiration. 3.) in overly dry soil, the effect on most plants is more obvious. Conversely, water-logged soil with poor drainage has a suffocating effect on most plants and organisms. 4.) limited sun exposure effects soil temperature, moisture level, etc. as well as diminishes plant’s ability synthesize carbohydrates, which also impacts Mycorrhizal fungi population and health, as that is what they get from plants, in return for the many benefits to plants, previously discussed.

Chemical weed killers are another significant contributor to soil acidification, decline of beneficial soil microbes, contamination of groundwater, toxic greenhouse gases, etc. and all the above stated. Most of what we refer to as “weeds” are annuals that spread by seed. And just like moss, often prefer soils plagued with poor soil structure, low fertility, nutrient deficiencies and acidic soils. All the conditions grass cannot thrive or establish in. In a way, they are a natural balancing and soil amending mechanism, providing organic matter back to the soil, thus over time, raising soil fertility, improving structure, etc. to levels more conducive to other plants such as perennials, grasses, etc. And just like the strategy I laid out for combatting moss by improving the soil to levels more favorable to grass, you are in the process reducing the conditions favorable to most weeds. Healthy grass ultimately will crowd out weeds as well. A combination of regularly replenished organic matter (mulch) to the soil, over-seeding and manual weed removal is really the best strategy for eliminating weeds from your lawn.

There are organic pre-emergent weed control products, such as corn gluten, available, that (as a bonus) also provides a nitrogen source to the soil as it breaks down. The tricky part of using corn gluten for lawns is that, as I said, it is a “pre-emergent” control. That is, corn gluten works by sticking to weed seeds, thus preventing them to further develop. The timing of use is what is tricky, as it closely coincides with grass seeding peak times and will have the same effect on grass seed. And also like moss, the presence of certain weeds in your lawn indicate specific soil conditions to be addressed, in order to amend the soil to conditions where grass can thrive and weeds decline.

Here are some common weeds found in Pacific NW lawns and gardens and what they can tell us about the soil.


  1. MOSS:  Acidic soil, low fertility, poor drainage, diminished airflow, shaded areas
  2. DANDELIONS:  high potassium, low calcium, acidic soil,
  3. CRABGRASS:  low calcium content, poor soil fertility
  4. GROUNDSEL:  nutrient rich soil
  5. CHICKWEED:  high nitrogen, nutrient rich soil
  6. CLOVER:  low nitrogen, acidic soil, low fertility
  7. PLANTAIN:  low fertility, compacted soil, dense clay, acidic soil, high calcium, phosphorus, potassium
  8. CREEPING BUTTERCUP:  water-logged soil, poor drainage, acidic soil,
  9. OXALIS (WOOD SORREL):  low calcium, low nitrogen, low phosphorus, high, potassium
  10. RAGWEED:  poor fertility
  11. MULLEIN:  acidic soil, low fertility,
  12. SHEEP SORREL:  poor fertility, low calcium, low nitrogen, dry soil, acidic soil
  13. PURSLANE:  low, calcium, nitrogen and phosphorus, poor airflow, low moisture
  14. HORSE-TAIL:  poor drainage, clay soil, low fertility, acidic soil, low calcium, phosphorus
  15. LAMB’S QUARTERS:  high nitrogen, low phosphorus
  16. BLACK MEDIC:  low nitrogen, compacted soil,
  17. CARPETWEED:  high nitrogen, phosphorus, potassium
  18. MALLOW:  high potassium, low nitrogen, phosphorus


The prolonged use of chemical fertilizers ultimately results in an unravelling of soil health and stability that yields a long string of negative symptoms such as disease and infestations when soil microbial balance is altered, conditions less conducive of sustaining grass and other plant life (aside from weeds, of course), etc. If your lawn is exhibiting such symptoms, as precipitating from chemical overuse, the only way to correct the problem is by regularly rebuilding soil structure and nutrient content back in the soil by adding 1/2” of fresh mulch to your lawn and over-seeding twice a year (6 weeks minimum before first frost and right after final frost dates, until soil is stabilized and better able to largely sustain itself. Grass needs a minimum of 3“ – 4” of healthy topsoil to survive. If you are consistent with a twice annual routine of mulching, expect a least 3 – 5 years to correct soil conditions and damage from chemical fertilizer use.

Regular mulching is also important, if you are regularly cleaning up fallen leaves and other dead plant material, as this is the primary source for feeding and stabilizing soil ecosystems in the first place. Without it, you will need to add it. The upside is that once you have reached the desired soil health, fertility stability and structure, the frequency of requisite regular mulching need not be as often as twice a year, necessarily, though as needed is recommended. Organic fertilizers can be used in combination with added mulch to help replenish nutrients, but it is important to understand that they are slow released, as they require the participation of other key players in soil biology and the gradual progression of improved soil conditions, which takes time. Also remember, organic fertilizers are not a substitute for mulching! The goal is healthy, balanced, rich soil that can largely thrive on it’s own, with occasional assists from us, on the sidelines.

And just as there is no way to, say, take an elevator directly from the basement to the top floor, expect a string of ever evolving conditions to emerge and acquiesce as you reach your ultimate destination. Good, consistent “soil stewardship” is key to a healthy, stable and productive lawn and garden. In fact, it is the only option, under the circumstances, but fear not…

Your patience will be rewarded!!

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