I chose the Container Gardening Forum to post this, simply because it's my favorite hangout. My hope is that anyone reading this will come to its end with a better understanding of some of the limiting factors our plants are subjected to, and why one potentially limiting factor cannot make up for another. I hope you enjoy ...
In a recent post, I explained why light, or any other factor, could not make up for or 'trump' the negative affects of other factors that could potentially limit plant growth. Liebig's Law of the Minimum is a universally accepted concept that defines how the growth of plants is limited. Originally the law was viewed by Justus Von Liebig, a German chemist who is often referred to as 'the father of the fertilizer industry', as a fitting way to define the fact that plant growth is not limited by the total of the available resources, but rather, by the single resource in shortest supply.
Though Liebig's focus at the time was on nutrition, his concept was later expanded to include other limiting factors as they were discovered. Not only are each of the elements commonly regarded as essential to plant growth recognized as having the potential to individually limit growth, but the law has also been expanded to recognize the limiting effects of cultural conditions like light, temperature, levels of soil moisture and aeration, insects, disease, and others.
Liebig used a barrel with staves of varied heights, like you see in the picture at the bottom of this post, to illustrate how his concept worked. Imagine the barrel also has additional staves for light, soil moisture/aeration, temperature ... for each and every potential limiting factor, insects and diseases included. As you view the picture of the barrel, you can see that Liebig is illustrating in this case, that N is the limiting factor. The plant is not growing as well as it could be because it is N deficient. When we add more N, and N is no longer the nutrient or potentially limiting factor in shortest supply, something else takes its place as the limiting factor. Even if the supply of N was increased to the point where it was in perfect supply, the least available nutrient or cultural condition would STILL be the limiting factor. We raise the stave representing N, but then another stave representing another resource becomes limiting. Note that it appears phosphorous and calcium are potentially the next most limiting factors.
You can see that if light levels, temperature, other nutrient levels, are made perfect, it still wouldn't/couldn't compensate for the effects of the N deficiency or other limiting factors. The same is true of soils. The most perfect soil we are able to build will not make up for or 'trump' the effects of a nutritional deficiency or poor light.
Our goal then, is to try our best to make sure ALL the cultural conditions are optimum - making ALL the staves taller, as it were. It doesn't do us any good to make all but one stave taller, because it is that pesky short stave that is going to limit growth - EVERY SINGLE TIME! Surprisingly, it is not as difficult as it sounds.
Light and temperature are actually very easy. The onus of learning your plants' preferences for these cultural conditions is on you, but they are very easy to learn and easy to correct, so that issue needs no more attention. Insects and diseases might be a little tougher, but IPM practices are derived from common sense. Identify the pest/disease and use the least noxious remedy possible to reduce the problem to something below your tolerance threshold.
Modern fertilizers make it easy to supply nutrients at near optimum levels and in a ratio to each other that is favorable. Tucked into Liebig's Law is the fact that too much is as bad as not enough, so there is incentive for us not to cater to the idea that because a little is good, more is better. As we look at the barrel example, we can see that increasing the N supply so the N stave is taller than the P or K staves is not going to help. So, using fertilizers with a favorable ratio and applying them wisely is actually something we can all manage.
Because this is the Container Gardening Forum, the most frequent source of trouble and the issues that arise with the most frequency are soil related. Soil moisture and aeration are staves as critical as any other in the barrel. Just as a perfect soil cannot 'trump' the effects of other short staves, optimizing other conditions cannot offset or 'trump' the effects of a poor soil. The necessity of making sure your plants are adequately supplied with water is an obvious given. The effects of excessive water retention and inadequate aeration are widely discussed on the forum. You can learn how to avoid these issues entirely or almost entirely by reading about How Water Behaves in Container Media by clicking this highlighted text: http://davesgarden.com/community/forums/t/1073399/ or you can read some tips about
How to Deal With Water-retentive Soils by clicking on this highlighted text: http://davesgarden.com/community/forums/t/1128179/
Do keep learning. The more you know about how your plants grow, what cultural conditions they prefer, and the effects varying cultural conditions will have on your plants, the better equipped you are to deal with them, keeping all the staves tall and minimizing limiting effects.
I wondered if anyone would notice - or comment. I figured the information and the perspective on growth was another of the frame pieces, which is why I posted it. If anyone wonders what 'frame pieces' refers to you'll have to ask. ;o)
This reminds me of Frances Moore Lappe's argument in Diet for a Small Planet. She explained that most proteins were incomplete and that the adequacy of any protein (for humans at least) is limited to the level of the amino acid in shortest supply...If I read your article correctly, the thinking is much the same. That no amount of any nutrient is adequate unless it is supplied in the correct ratio to all of the others...?
I think you're correct in the way you compare Lappe's reasoning to Liebig's; and I would probably have agreed completely if you'd left out the word 'ratios', as it wasn't really ratios I was driving at. While favorable nutrient ratios can be a major plus, a perfect ratio can also be maintained at either deficiency or toxicity levels. I know this might be confusing, but if we consider only nutrients, and take as a given that they are all supplied in a perfect ratio to each other, if they were supplied either at deficiency levels or in excess, they would all be equally limiting; but that would only be true of there was not another factor that was more limiting, which would make both the ratio and the level of nutrients available a moot point.
It's important to remember the list of potential limiting factors encompasses influences other than nutrients. Light, temperatures, moisture/air levels in the soil, insects, diseases, all are potential limiting factors. If it was possible to have two factors that shared equally the distinction of being the most limiting, improving only one would not improve growth.
This may be WAY off base, but I heard a discussion on the Today show that explained how so many of us are vitamin D deficient, which can lead to CNS disorders, among other things. They explained that it is fat soluble and protein is also required for our bodies to correctly up-take D. They also said to take it with your biggest meal, if you are using a supplement. They pointed out that no matter how much you take if you aren't taking it with fat or protein it can't be made completely available to your body.
I guess what I'm getting at is that while many people are vitamin D deficient it may not be do to lack of sunlight exposure etc. but rather our obsession with low/no fat foods.
My limiting factor for plants is pests, that I know. But I live in Texas so I'm not alone. LOL
Al, thank you so much for the info. I've been lurking and have learned so much.
Hi, Lisa. How nice it is to see you abandon the lurking in favor of joining us!
I think one of the points we can take from your offering is that when it comes to growing things, all things are not as they at first seem. More times than I can possibly count, I have seen advice to do this or that, that makes no sense from the scientific perspective. In the same vein, observations made that attribute an affect to an impossible cause are extremely common. The more pieces of the puzzle we have to work with, the easier it is to see the big picture clearly, which is why learning is so beneficial to increasing our effort:reward quotient.
I recall your listing the factors that affect plant growth (eg: soil, water, light, nutrients, etc.) on another thread along with some discussion. Would you please list them again here or provide a link to the information where it resides.
I think you've listed the big ones, other than temperature. Insects and disease need to be added as potentially limiting as well. In certain cases pH itself would be a limiting factor, but in others, it might be the nutritional deficiencies or toxicities resultant of an unfavorable pH range that would arguably be to blame.
The point I wanted to make is, there are a number of factors that have the potential to limit growth, and unless you improve the most limiting factor, it doesn't matter if all other factors are made perfect ... it's still that stinking superlative, "most limiting", that will lay you low every time. ;o)
I found this post fascinating. I really learned something. However, I would like to say that for the people who are new at all this, it can be difficult to even THINK of all the factors that could be limiters. In my mind, it would be:
Pests (bunnies and bugs where I live)
But then I read things about phosphorus and calcium and I swear someone just sent me an advert for plant carbohydrates! This means my list of "staves" is incomplete. Where would I find an easy list of factors, do you think? It's all so overwhelming at first, but I'm going to green my thumb if it kills me.
Cynical, I have learned a lot about soil from one place in particular: Dr. Earth... What I've learned from Milo has turned my black thumbs green. Here are a couple of links that tell quite a bit about the structure and components of soils:
I do numerous presentations for various groups, clubs, organizations ... in the span of a year. Recently (last month) I was scheduled to lecture on various aspects of houseplant care to a local chapter of the Women's National Farm and Garden Club. Since I originally posted this thread, I had something of an epiphany while considering a reply to another thread in which I invoked Liebig's Law, and in doing that suddenly realized that we are defined as growers by our ability to identify and eliminate the effects of limiting factors. If you consider for a moment that we are virtually assured that every plant we grow, unless it's from seed, has the genetic potential to grow well, produce well, and look beautiful. As an example, every houseplant we ever bought, left the greenhouse as a beautiful specimen, so we KNOW it has the genetic potential to grow well and look beautiful ... if we just get out of its way. ;-)
What I mean is, if we were able to provide perfect conditions - the plant would be perfect. Since we're never going to find the exactly perfect combination, how close to perfect our plants are is determined at how close to perfect we can make the conditions under which the plant grows. It's through our ability to eliminate and reduce the effects of limiting factors that we earn our green thumbs - nothing more than that. We just never realized it because it's never been put into those terms. I have never read that perspective or heard it offered before, but I doubt that anyone would disagree.
Obviously, it's to our advantage to work on the most commonly known limiting factors, or those we've identified as limiting first. For container gardeners, I think that eliminating the effects of a poor soil represents, hands down, the most potential for improvement & deserves first consideration. The roots are the heart of the plant, and it's impossible to have a healthy plant without a healthy root system.
After the limiting effects of soil choice and watering habits are reduced to your satisfaction, something else is going to be 'limiting'. You'll need to work on light, temperature, nutrition, and a few other things, but they are all surprisingly easy. I would never encourage someone to blindly follow directions without knowing why, but it is a fact that if you give a novice grower a very good soil, instruct him/her to keep the plant in the sun (if appropriate) and water it in a certain way every time the soil is nearly dry with x number of drops of fertilizer per gallon of water, that that grower can bring along very beautiful plants from the outset ... at least until something changes that calls for adaptation, at which time the novice would be at a loss.
The point is, it's all very easy. WE just make it harder than it has to be through our not always ideal choices.
Lol - I don't know if this is interesting, or if I'm just flapping my jaws. I get accused of that from time to time, but as you can see, I remain undeterred. I know that last month when I presented the concept that our plants know what they're supposed to do, and they want with all their genes to do it - all we need to do is get out of their way and help them a little by taking care of those things that limit their ability to fulfill their genetic destinies, there were a lot of people having 'AHA!' moments or HUH! - I never thought of it like that' moments. What say you guys?
Al, that was very well put. Don't know how I missed the thread when it was first posted as I have a great respect for your knowledge. Guess because I don't peruse the Container Gardening forum very often!
Thank you very much for the very kind words! I think people often put the cart in front of the horse and put a lot of faith in the advertising hype they read instead of concentrating on the basics. The biggest problem is no one ever defines the basics for you, and you're left to learn everything by trial and error. Being bit on the butt by our mistakes really is a poor way to learn ... agreed? ;-) The miracle soils you read about on the packages, and the promises of the magic elixirs aren't going to turn you into a good grower. And honestly, experience isn't going to do it either. I have people who have been growing in containers for sometimes 50 years bring me plants that are in appalling shape for a 'diagnosis'. I can usually tell at a glance what the problem is, and it's almost always related to root health/function.
The problem is, there are soo many variables you almost never know what you did wrong. The answer to that problem is to concentrate on getting the basics right, and your plant's health starts with it roots. In order for roots to be healthy, you need to use a healthy soil or understand how to work with a poor soil. Getting it right from the beginning means you won't need to deal with the problems the forums are full of. You don't need more than 1 soil, and you don't need more than one fertilizer; and all the other little things you try are actually more likely to be limiting than a benefit, and won't 'make up' for other limiting factors overlooked. If you can get your soil, fertilizer, watering habits, and light right, and use good judgement when it comes to temperature and a couple of other factors that common sense should take care of, you're going to be a better grower than 90% of the rest.
If you take just a little time to understand the soil concept, the rest is really very easy.
tapla wrote: The biggest problem is no one ever defines the basics for you, and you're left to learn everything by trial and error. Being bit on the butt by our mistakes really is a poor way to learn ... agreed? ;-)
You don't need more than 1 soil, and you don't need more than one fertilizer;
Yes, indeed! Learning everything by trial and error gets expensive, which is related to your words about 1 soil and 1 fertilizer. Those manufacturers of garden products just keep on keeping on with new and improved stuff...
I'm with Koshki Al, I'm really gonna have to find and read all your posts, you've got such good common sense stuff to say.
It drives me slightly buggy when, at work, I try to explain to people that their soil is alive, and the better they take care of it and feed it, then IT is what will feed their plants. I can see in their shifting eyes that they've tuned me out at the word 'alive'. They'll be back in two months wondering what they did wrong with this or that dying plant, and when they tell me about the Miracle Gro they're putting in the soil I'll wrap 'em on the wrist with my pruners!
Speedie-from what Ive read of Als posts there is nothing wrong with MG, correct me Al if Im wrong. Its lack of Organic Material in the soil, but this does not pertain to container gardening. Fertilizer is fertilizer to a plant. The plant cant tell if the nutrients are synthetic or not. Nitrogen is just Nitrogen to a plant.
Lisa's correct. You don't need a soil that's alive at all. If you bet me, I'll grow a perfectly healthy plant in nothing but broken glass to prove the point. Container culture is soo much different than growing in the garden. If we were discussing our gardens & beds, I'd be on Speedie's side, but container culture is much closer to hydroponics than growing in the garden. I've posted hundreds of pictures of perfectly healthy plants, all brought along in a soil that is 2/3 inorganic and using nothing but 1 synthetic fertilizer. In fact, I don't WANT to feed my (container) soil. Large populations of microorganisms simply break the soil down faster, causing structural collapse of the soil. The MOST important aspect of your soils isn't the nutrition they supply, that's an insignificant consideration because you can supply everything from a bottle or box, it's the soils structure; more specifically, it's how well it maintains a favorable volume of air in the soil and adequate amounts of water WITHOUT that soggy layer of saturated soil at the bottom of the container (the perched water table). Simply put, saturated conditions kill roots and impair root function and are probably the number one limiting factor you guys are dealing with. You would be amazed at how easy growing is when you use a quality soil.
This is what I grow all my houseplants in, and it has only a small amount of bark as an organic fraction ... and the only reason for using the bark is because it's less expensive than the other two ingredients and I use a LOT of soil - hundreds of pounds each year (because of all my bonsai repots).
Al, Is MG a satisfactory fertilizer for inground planting as long as Organic Material is added also? I started a thread here, awhile back, regarding Synthetic Fertilizer killing the biology of the soil. I believe your answer was that it wasnt the synthetic fertilizer but lack of OM that "kills" the soil. Something like that. LOL
Oh dear, my apologies, I got a bit off-topic with my comments and didn't clarify. I wasn't referring to container soils/plants, but in-ground plantings. I really do need to learn how to stay on-topic. < =/
Al, I'm 100% with you on the container plantings, we've got some Bonsai at work that are in nothing but some sort of rock composition. (I've got no idea what all is in it, I'm a million miles from knowing what I have yet to, and *want* to, learn). :)
And yes, then there's hydroponics... but, water is an Organic Material, no? ;P ... maybe not so much these days, huh? heh heh.
You pay attention, Lisa. ;-) That's right. Synthetic fertilizers don't harm soil life, they actually increase it. I'll post the reply at the end of this offering in case anyone is interested.
Speedie - determining if something is is considered an organic compound pivots on whether or not its molecular structure contains carbon, so water wouldn't qualify as an OC.
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 options are good, and I prefer to keep mine open.