Organic fertilizers vs. chemical fertilizers ???

Molokai, HI

The basic concepts of organic farming seem solid but on one point I have some questions. A horticulture professor and friend of mine taught me that plants need to take up nitrogen, phosphorous and potassium in their chemical forms to grow. The plant’s roots can’t tell if these chemical are derived from chemical fertilizers or organic sources, like manure. They utilize chemical molecules only. If so, I am compelled to ask, “What is better about using Bat Guano versus using Miracle Grow on my vegetables?”

Bernie Strehler Molokai Hawaii

Charlotte, NC(Zone 7b)

Bernie, I've been gardening the organic way for 60 years, and quite honestly I can't easily answer your question.

To me, it's all about the soil being a living thing. Millions of microbes live in organic soil, plus earthworms, and other critters. Together they break down the organic fertilizers, compost and mulches that are added to the soil and turn it into something your plants can take up as nutrients.

Organically grown plants are much more able to resist diseases and attacks by bugs. Why this is so, I don't know, but it's well documented.

I can only tell you that gardening organically works! Feed your soil and your soil will feed you.

Every time it rains, chemical fertilizers get washed away from the soil and into our creeks, rivers, and eventually the life blood of our planet - the ocean. Organic fertilizers break down slowly and are harder for the rain to wash away.

It has never occurred to me to garden any other way. I don't spray with pesticides, herbicides, fungicides or any other "cides" - and I've never had a crop failure or gone hungry :)

photo taken June 2010

Thumbnail by HoneybeeNC
Bay City, MI(Zone 6a)

I'm going to approach this issue by looking at it from a growth perspective. IOW, what will make my plants grow best, and what will ensure that they are able to grow as near to their genetic potential as possible. Politics and ideologies aside, I'm hoping that the reasoning will be viewed as sound. This is about gardens and beds ..... not agribiz.

In my gardens and beds, I adhere pretty strictly to the idea that on an ongoing basis we should use organic products/soil amendments that build the soil structure to minimize the need for soluble (read synthetic) fertilizers and nutrient supplements. That said, there are times we need individual nutrients to complete the assortment of essential nutrients plants take from the soil. If you're limited by a rigid 'no chemicals' ideology, you either deal with the abnormal/sub-par growth associated with deficiency ..... or wait, while you hope the organic matter you've added eventually solves all the issues. If, on the other hand, you are NOT limited by rigid ideology, the issue is easily solved with a soil test and the addition of the appropriate nutrient(s) via a chemical compound like potash, various nitrates, phosphates, etc.

There are extremists at both ends of the organic vs. chemical approach to gardening. Some never think about the soil, believing it just fine to depend on the continual addition of chemicals to 'hopefully' produce growth. Others would never even THINK of using a chemical, and will chastise anyone who does. When it comes to my gardens and beds, I'm in the middle, but as noted I do lean quite heavily toward the organic side, though I stop short of telling anyone what they must do to be a good gardener.

Briefly: where container culture is the topic, soluble synthetic fertilizers get the nod from me - hands down. They are easier to use; we know exactly what nutrients our plants are getting and when they are getting them; delivery of nutrients does not depend on the activity of soil organisms whose populations vary in boom/bust cycles in containers; you're using a soluble product, not an organic soil amendment that has the potential to clog valuable macro-pores; you need not worry about soil structure, because if you are smart you will have built it into the medium before you planted in it ...., but let us save the container soil topic for another day.

I mentioned there are those at one end of the spectrum who would never lift a finger to improve their soil. Adding organic matter to their soils would be as foreign to them as adding exercise to life's itinerary. On the other end, are those who stand ululating and hand-flapping (credit to Dan for that one) at the very thought of anyone using Miracle-Gro. From the plant's perspective, both extremes are ridiculous, and from my perspective, both extremes are unnecessarily self-limiting. The plant just wants to grow to its genetic potential. To do that, it needs a soil that supplies the right amounts of air and water (good structure), and a full compliment of the nutrients plants take from the soil, and it doesn't care if they come from compost or Miracle-Gro.

Perhaps a more logical approach to plant nutrition might be to look at soluble synthetic fertilizers in the same way we look at IPM practices. Use the most naturally harmonious method/product we can to ensure plant growth or yields are in what we determine to be the acceptable range. I realize that in most cases, we can do this by adding more OM, but not always. Often too, time is a consideration. We may have someone who wants to plant immediately, in soil that is deficient in one or more nutrients. We probably shouldn't expect someone to forgo their own freedom of choice and wait two years or more while the soil is fortified/improved only via the addition of organic matter, just so they don't have to suffer the wrath of someone who might not think them 'green' enough to join their club.

There is a technical difference between a fertilizer (Miracle-Gro) and a soil amendment (feather meal), but even that point eventually becomes moot from a strictly nutritional perspective. Plants take up elements that are dissolved in the soil solution and in ionic form. What they take up are salts. The large molecules that make up hydrocarbon chains in organic fertilizers/soil amendments cannot be taken up by the plant unless the hydrocarbon chains are broken down into elemental, soluble form by soil organisms. At that point, the elements from soluble fertilizers are the same as the elements from organic sources, which is why the plant could care less. At the point in time where nutrients are assimilated, they are ALL soluble and in elemental form, regardless if they came from a dead fish, compost or a hose-end sprayer.

If we could only achieve happy healthy plants in a soil teaming with life, using only organic soil amendments and fertilizers, how do we explain hydroponics? ... no medium, or an entirely inorganic one, and only soluble sources of nutrients. At the very least, hydroponics suggests there is a middle ground in which everyone can seek their comfort level.

For more than 20 years, I have been growing perfectly healthy plants in containers, using a medium whose only organic fraction is 1/3 or less pine or fir bark; the rest of the ingredients are large mineral particles like Turface and crushed granite. I have used ONLY soluble fertilizers in these soils, with the hundreds of pictures I have posted here at GW serving as concrete proof that happy, healthy plants can indeed be grown using only synthetic soluble fertilizers, if the soil structure is favorable, which leads me to the reason for writing this:

Colloquially, the term 'organic' formerly applied to things once living, but even some plastics contain carbon and are considered organic compounds as well. It really is misleading when we throw the word around w/o much consideration, but I admit to being guilty of it from time to time as well. Technically, urea, ureaformaldehyde, isobutylidene diurea, and crotonylidene diurea (forgive me if the spelling is slightly off) are all organic molecules, and actually do an extremely good job of feeding microbes, which strongly reinforces the idea that synthetic fertilizers are getting framed for the microbial murder rap that should be hung on the effects of reduced OM in the soils. The microbial murder rap should be hung on the effects of reduced OM in the soils; purposely redundant so it could not be missed.

It's a vicious circle - mineral soils can support optimal plant growth (nutritionally speaking) only if enough young decaying matter is returned to the soil regularly and frequently. Prairies and forests are virtually self sustaining because all vegetative matter is recycled back into the soil. If we regularly mow and bale the grassland, or log off the forest, nutritional deficiencies are assured as a result of our removal of the OM that would have provided future nutrition - thus the tendency/need for us to adhere to the practice of replacing the lost nutrients using chemicals. Perhaps I should put that another way - .... replacing the deficient nutrients using chemicals.

To be clear, this isn't a 'What came first, the chicken or the egg' thing; it isn't the fertilizer chemicals that causes the ravishment of the soil, it is the ravishment of the soil that is causal of the necessity/tendency to use the chemicals, particularly where expedience is key.

In our gardens/beds/lawns ..., we can add compost or other OM to replace the vegetative matter we remove and use or discard. For more than 20 years, I've used compost regularly in the gardens/beds, and applied fine pine bark mulch 2-3" thick, usually every other year. I have extremely healthy soil and rarely find it necessary to use anything synthetic.

You can find opinions all over the net that chemical fertilizers are laying waste to the landscape, and wiping out microbial populations faster than chocolate disappears from the candy dish in the family room. Are these opinions based on political views and a radical ideology, or warranted and based in fact?

In research by Texas A&M University, intensely managed (read 'managed using chemical fertilizers') sports fields with mostly a sand substrate showed no shortage of soil life. That is there were 10s of millions of bacteria, and 10s to 100s of thousands of fungi per cubic centimeter present in the heavily managed soils. Part of the study included measuring soil life in 11 inches (deep) of pure sand that contained no additional organic amendments whatsoever, over which washed sod was placed. As the sod 'grew in', soil life populations increased almost immediately, 10-100 times their previous numbers.

Soil life populations just sort of hang loose, waiting for something they can digest. If they don't get it, they die and feed off each other. When organic matter is introduced into the soil, they break it down, and their numbers increase. When they've consumed the organic matter, they die and consume each other, but the base population remains, ready to spring into action the moment more organic matter becomes available.

What do soluble fertilizers do? They make plants grow. Sure, extremely high concentrations of chemical fertilizer poured on the soil in volume might kill some microbes in the immediate area, but the o/a affect of chemical fertilizers is actually an increase in microbial populations through increased plant growth/mass. You need only look to the fact that the rhizosphere (root zone) of plants is such a popular gathering place for soil biota to see increased plant mass promotes a marked increase in soil life. It's actually the continual 'taking' of OM from gardens, agricultural fields, lawns ... w/o replacing it that reduces or inhibits the communal activity of microbial populations; even then, they are ever ready to bounce back ... if you just give them something to eat.

None of this addresses the hot button political, ideological issues too many wish to export from their own value set, other than the fact it points out the folly in occupying the margin's extremes. Again, I'm pretty pragmatic and results-oriented, so I tend to approach this subject from a plant/soil/growth perspective and leave the politics to the ideologues. My personal view is that in the o/a picture, a chemical fertilizer or nutrient supplement judiciously and responsibly applied to our gardens when it's found to be needed isn't the earth's end; and I prefer to use my own sense of right/wrong to set my course, rather than be told what I need to do to be a good, responsible student of husbandry.

That said, avoidance of unnecessary chemicals in the gardens/beds to the greatest degree I feel is reasonable, is still my normal MO. YMMV, but having options is a good thing, and I prefer to keep mine open.


This message was edited Oct 10, 2011 11:41 AM

Molokai, HI

HoneybeeNC, thanks for your candid comments and sharing your perspective and good common sense about healthy soil and plants. (Nice photo of your healthy garden too!) To tapla, thanks for the very comprehensive, well rounded tour of the issues you provided. You are the first to mention the phenomenon of hydroponic gardening, which seems an interesting puzzle in the scheme of things. Your comments are so well written by the way I think they could stand a larger audience - like a letter to the editor in some venue. Any way, thanks very much!

Bernie Strehler Molokai Hawaii

Arlington, MA(Zone 6a)


you may also want to consider the manufacture of the products you are considering using. i like using products that would otherwise end up in landfills or other waste streams.

(i can't really add more to Al's analysis.)


Provo, UT(Zone 5a)

i use a mix of "organic" and traditional/commercial prepared fertilizers.. and have good
success with it..
but... LOL... when my plants seem to need that extra ..bump/kick start..whatever to put on
big size.. my homemade manure tea always seems to do the trick...
?? i know my experience is totally unscientific.. untested..(except from my own experiences)
?? anyone else have similar experience??
my soil is well drained..i live moderately near a river.. so i have a TON of rocks below my soil
i have composted for over 15+ yrs.. i have ALOT of good humus in my soil..
anyways..i dont know if its the combo of my soil and the manure tea.. just is what it is..or what..
but this yr..some of my tropical plants have been sort of puttin along.. so last week i gave them
a doze of manure tea.. gave 2nd doze 3 days ago.. and they are showing signs of.. waking up..
i do think this yr is that its been extrememly HOT..and DRY.. so i know that has had
some affect on my tropicals..
anyways..?? anyone else find manure tea peps up your plants???

Are your tropicals growing in pots? I was wondering about giving my plants, both in the ground and in pots, some worm compost tea but wasn't sure if it was okay because it's been so hot and dry here. I've read that fertilizing during hot spells is not a good thing but we've been warmer than usual since spring.

Provo, UT(Zone 5a)

most of my tropicals are in the ground..i ran out of room so some got left in pots..LOL
ya..i dont fertilize during the hot part of the day..either early morning..or after 7pm.
let us know if your plants respond to the worm tea ... :)

Dublin, CA(Zone 9a)

I think the cautions about fertilizing in hot weather are probably more for chemical fertilizers that are higher concentration and can burn the roots, etc. With organic things like worm tea the nutrients are more diluted so I don't think there's really much possibility for causing problems. So I'd go ahead and do the worm tea, might not help if it's so hot that the plants really don't want to grow, but I don't think it would hurt anything.

Charlotte, NC(Zone 7b)

Having lived in South Florida for a good portion of my life, I can tell you that the one thing tropical plants love is humidity! If you can give them a fine mist of water throughout the day, they should thrive.

Tropicalnut - thanks for more guidelines. Mine are in pots since I have to move them indoors in the winter. And I was thinking that my poor tomato plants probably need a boost as well.
ecrane - thanks for the clarification on the fertilizers. I know that some chemical ferts do contain a lot of salts which probably isn't so good when it's hot but I was hesitant about any and all when it's this hot and dry as I'm not trying to necessarily encourage lush growth but more to keep things healthy enough to deal with weather-related stress.
Honeybee - no way currently for me to frequently mist plants here unless it's by hand. Mandevilla is handling the heat well here but blue sky vine - not so much.

Provo, UT(Zone 5a)

good luck to ya cindy.. its a hot summer for sure for most of us..
here utah..were huffering in mid 90sF we had some humidity last rain..:( bummer
i agree with honeybee on humidity.. one thing im doing is wetting the soil really well.. it does raise
the relative humidity around my tropicals..and they do appreciate it.. :)
also helps in my dispersal of fertilizer..i just let it run everywhere around the plants..and i think its helping
some..?? we'll see in couple weeks..we still have till early oct here before i worry about chilly temps..

Humidity today is around 71% with 93 degree temps forecasted. Ugh. The only plants that I've used granular fertilizer on this summer are the vegetable plants and that was with Dr. Earth starter fertilizer (2-4-2) - low enough not to overly-encourage growth when it's hot.

Pueblo, CO(Zone 5b)

I don't like the word "organic" because it does mean different things to different people. I had enough chemistry pounded into me as a kid that organic will always mean "contains carbon" to me. That makes petroleum products organic and granite sand not. Then the the common usage came to mean "no synthetic chemicals" I guess.
Here the soils tend to be high in salt, so fertilizing with manure is not recommended. So there is a new definition here. When a landscape supply company sells "organic" compost, it contains no manure, while regular compost is made with composted manure.

I agree about that term "organic" when it comes to garden amendments and fertilizers so I check the ingredient list or if there's any OMRI logo. I don't often buy compost, trying to make my own, and mulch with shredded fall leaves.

Warrenton, VA

I have to say that I am confused as I try to be as organic as possible, and believe in Espoma products, but have had experts warn about the high salt content in most organic products, especially Espoma. YIKES!

Bay City, MI(Zone 6a)

Many growers are burdened with the idea that salts are necessarily bad, but all nutrients are taken up in the form of salts. We know that plants make their own food, and that fertilizer is not plant food ..... but if it was, we could say that a plant's diet consists entirely of salts. Problems occur when the o/a level of EC/TDS (electrical conductivity/total dissolved solids) is too high/concentrated in the soil solution, or when the ratio of one or more nutrients to the remaining nutrients is skewed. The poison is in the dose. Dissolved solids in the soil solution that add to the EC/TDS of the soil solution w/o providing useable nutrients are particularly bad, which is a very good reason to get your soil tested so you're adding only what's deficient. Choosing a fertilizer off the shelf w/o knowing what your plants actually need inevitably leads to limitations - it has to; this, because anything supplied in excess can be as limiting as a deficiency.


Sierra Foothills, CA(Zone 8a)

Thank you, Al, for reminding me to have my soil tested. Any place better, or are home kits enough?

Bay City, MI(Zone 6a)

Try the U of C County Cooperative Extension Service

Central Sierra Cooperative Extension
311 Fair Lane
Placerville, CA 95667
Phone: 530-621-5502
Fax: 888-764-9669


Sierra Foothills, CA(Zone 8a)

Thank you!

Mandaluyong, Philippines

The environment has provided natural pesticides and weed repellents in the form of insects and other creatures used as fertilizers in organic gardening. While modern synthetic fertilizers cannot differentiate both good and bad insects, thus killing both parties resulting in unbalanced soil foundation.

Aside from the fact that chemical substances and modern fertilizers can cause harm to the body, they are also hazardous to the environment. The chemicals used in synthetic fertilizers are responsible for air and water pollution, as well as impeding the nutrients in the soil over time. Conversely, organic farming upholds the preservation of balance in the ecosystem.

Bay City, MI(Zone 6a)

What I got from your comments is, you feel there is no room for anything other than the "all organic" approach. That's fine, if you prefer to limit yourself to those methods. I didn't understand several of the comparisons you made, comparing fertilizers to insecticides to 'weed repellants' ....... and using exclusively organic methods doesn't ensure the 'preservation of a balanced ecosystem' by any stretch. In fact, in some cases when returning only local OM to the soil it might be impossible to achieve a chemically balanced soil w/o a soil test and the addition of inorganic substances that specifically target deficiencies.

I'm not arguing for the use of chemicals or against an all organic ideology - I'm, simply saying that some degree of flexibility leaves you choices from both sides of the aisle, which is better than being so rigid you can't employ the methods that most expediently allow you to achieve the desired end. That 10 yard purchase of manure and mushroom compost you might have piled on a slope while it finishes composting before going on your garden is going to do a lot more harm to the environment that the little bit of Miracle-Gro fertilizer solution that leaches from Suzy's half dozen containers of mixed flowers or veggies.


Belmont, Australia

I tried coco peat for my garden. Coco peat with balanced nutrients and pH can help a lot to boost the soil biology. It also saves the water usage. So I think it is the best way to grow the plants organically with less use of fertilizers.

Pueblo, CO(Zone 5b)

And I am in another category. I avoid ALL insecticides (even organic ones), and most herbicides (I spot treat bindweed). But I don't have any problem adding granular fertilizer with extra phosphate to my low-phosphate soil the first time I prepare a bed - I also add lots of low-sodium organic matter at the same time.

Grants Pass, OR(Zone 8a)

I have been doing a lot of research on soil and soil organisms. A few things showing up in new research around the world are quite interesting. Mycorrhizal fungi form symbiotic relationships with plants. They break down the minerals and some other substances in the soil and make them available to plants in a form they can use without further processing. There are also many forms of nitrogen fixing bacteria in the soil, as well as organisms that fix phosphorous as well. Research is showing that synthetic fertilizers interrupt almost all of this natural process. Synthetic nitrogen has been found to quickly kill Mycorrhizal fungi and many other soil born organisms including the nitrogen fixing bacteria.It also breaks down into salts that can over saturate the soil (turning farmland into desert) preventing or hindering plant growth if the levels get high enough. Synthetic Phosphorous does not seem to kill mycorrhizii but it does disrupt its process. It also interferes with many other soil organisms which tends to allow the disease type organisms to get a stronger foothold. Synthetic fertilizers are touted as problem solvers for nutrient deficient soils but actually cause (especially with prolonged use) more nutrient deficiency by killing or disrupting the soil organisms that provide all these nutrients by breaking down soil and plant debris.

Bay City, MI(Zone 6a)

Links to that research, please?


Pueblo, CO(Zone 5b)

Chemistry 101 - basic elements of periodic table.
Phosphorus is phosphorus, potassium is potassium, nitrogen is nitrogen, iron is iron. There is no "fake" or "synthesized" form. It is the source and processing that determines how beneficial/harmful it is for the environment at the source and at the destination. And remember, heavy metals like like lead and toxins like arsenic are basic elements and can occur naturally - and do, here in mineral heavy Colorado.
And yes, Mycorrhizal fungi and other soil life are necessary for plant growth, especially natives. Our veggies are somewhat less dependent on them, especially crucifer/cabbage family.

With metals, I have had a concern with Roundup. It goes inert by binding with metals. I can't get a straight answer - does it make mineral-poor soils worse? (probably) Does it make trace heavy-metal water better - temporarily - then potentially release a burst of heavy metals if it breaks down again - say the water level drops and the mud is exposed to sunlight? (probably)

Bay City, MI(Zone 6a)

Just making sure that what you offered is your opinion.

If we could call the nutrients plants take from the soil "plant food", we could say that a plant's diet consists of salts, and it matters not a bit to the plant whether the salts it uses as building blocks come from compost, a dead fish, or from a hose end sprayer. It's all the same to the plant as long as it's needs for the specific salts are met.

I do understand growers voluntarily limiting themselves by adopting an all organic ideology, but an all organic approach isn't the easiest way to provide needed nutrients or maintain control over the nutrient supplementation program, especially if growing in containers.

BTW - plants establishing a symbiotic relationship with mycorrhizal fungi isn't all upside. Plants that develop these relationships have much smaller root systems than plants that don't. If ANYTHING happens to cause fungal populations to crash, which can actually occur as a result of adding OM, like manure) to your soil, you suddenly have a plant shedding parts because the root system is insufficient to support top mass.


Grants Pass, OR(Zone 8a)

Pollengarden, That is correct as far as the basic element is concerned. My point is that what we apply as fertilizers are various compounds of these elements. Many of these compounds (such as ammonium nitrate) do not readily form in nature and very rarely if at all in soil. Which is why I used the term synthetic. I am going back and searching for the original articles and papers that I got most of my information from. will post links when I get them together.

Grants Pass, OR(Zone 8a)

I have been using myccorhizal fungi for a couple of years now and my experience has been that the plants are bigger, more drought hardy and more disease resistant. I have not personally experienced any plants with reduced root systems but then again I have only a limited experience with different plant - soil - environment circumstances.

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