Dynamic accumulators, like comfrey, have become a hot topic. These plants are reported to have extraordinary powers to absorb more minerals than the average plant. This makes them very useful if you are trying to make nutrient-dense compost for your garden.
Imagine how great it would be if you could grow a plant that increases the nutrients you are lacking in the garden. That is precisely what people are doing with dynamic accumulator plants—or at least that is what is being claimed.
In this post, I will examine the idea of accumulator plants and try to figure out what they are. Do they exist? Do they add any real value? Is comfrey a good one?
Dynamic Accumulators: What Are They?
Let’s start with a definition. Wikipedia says the following:
“Dynamic accumulators are plants that gather certain micronutrients, macronutrients, or minerals and store them in their leaves.”
There are a few key points here. First, they are plants—a good thing since this is a gardening blog.
These plants gather nutrients, but the type of nutrients is not specified. The amounts that are gathered are also not specified.
The gathered nutrients are then stored in the leaves.
Given this definition, almost every plant is a dynamic accumulator since it absorbs nutrients and stores some of them in the leaves. An exception would be the leafless orchid. This does not seem like a very useful definition.
The Permaculture Research Institute defines dynamic accumulators this way:
“Plants (often deep-rooted ones) will draw up nutrients from the lower layers of the soil, and these nutrients will be stored in the plants’ leaves.“
Any nutrient in any amount qualifies, provided that it is taken from the lower levels of soil—whatever that means. Is 3 inches deep a lower level? Does it need to be 6 inches deep? Is it subsoil? This definition is also not very useful.
What is very surprising is that I was not able to find a better definition. Several other authors have also looked for a definition and the origin of the term. They concluded that “there are many definitions, all similar, and all fairly vague“. I also checked Google Scholar for scientific papers on the topic, and it seems scientists do not use the term.
The term ‘dynamic accumulator’ is used mostly by permaculturists, and they tend not to define their terms and ideas. The whole permaculture ‘thing’ is a very squishy, non-scientific affair where undefined terms are common—maybe even preferred.
By definition, dynamic accumulators are what you want them to be.
As an aside, the terms “biodynamic accumulator” and “dynamic nutrient accumulator” seem to be the same as “dynamic accumulator.”
Origin of the Term Dynamic Accumulators
Maybe the origin of the term will shed some light on our understanding?
Even this seems to be a mystery. The Permaculture Research Institute suggests that the term might have been started by Robert Kourik, who, in his book Designing and Maintaining Your Edible Landscape—Naturally, presented a list of dynamic accumulators.
If this was not the first use of the term, Robert Kourik certainly popularized the term by making the list of dynamic accumulators available. The list has been copied many times, with some modifications, and forms the basis of the current lists found on the internet. More recently, he said, “I no longer believe that list is useful.”
New Definition for Dynamic Accumulators
Since there is no good definition for dynamic accumulators, let’s create one.
A dynamic accumulator is a plant that will absorb and retain, in the leaf, at least one nutrient at levels that are at least 10 times higher than the average plant.
Where did the ’10 times’ value come from? I just pulled it out of the air. Without some value, the definition becomes useless. Given the variability between plants and soils, a tenfold factor seems reasonable.
Some might argue that an important point is missing from this definition since it does not talk about where the nutrients are gathered. Many people believe that dynamic accumulators have high levels of nutrients because they have deep roots. The deep root gives the plant access to extra nutrients. I’ll discuss this in a future post, but the idea that higher nutrient levels are the result of deep roots is mostly a myth.
Update: There is a new definition for dynamic accumulator, which is discussed in detail in New Science on Dynamic Accumulators and Weed Tea
Do Dynamic Accumulators Exist?
Given the established definition, the answer is yes—any plant fits the bill.
What if we use the new definition? The answer is still yes, but not all plants qualify.
There has been quite a bit of work done on hyperaccumulators and phytoaccumulators. These are plants that remove specific pollutants, such as heavy metals, from soil. Specific plants have been identified that are particularly good at absorbing things like lead or chromium. Once the metals are in the leaf of the plant, the plant can be removed from the site, reducing the contamination in the soil.
A hyperaccumulator is defined as “a plant that can accumulate 1000 mg/kg of Cu, Co, Cr, Ni, and Pb, or 10000 mg/kg of Fe, Mn, and Zn in its shoot dry matter”.
This is interesting, but does it really help gardeners? Are there plants that will accumulate the nutrients plants want? More importantly, can dynamic accumulators be used to improve the growth of other plants in the garden? These questions are explored in New Science on Dynamic Accumulators and Weed Tea.
Hopefully by now you may have read Gaia’s Garden. Toby Hemenway. Or:
Bill Mollison, David Holmgren etc….
I’m sure with your knowledge you can find their publications. Enjoy!
Kind Regards, Elizabeth
Why? I am more interested in actual science research.
A well written article with a fairminded, rigarous approach imo. However, your bias is shown most strongly by the assumption implied in the question (in comments section):
“What do you do when your observation is in direct opposition to science?”
Answer: You look to see how science can explain the observation and try and replicate the observations.
Afterall, science IS explaining observations and trying to replicate them.
Put another way, an observation cannot be in opposition to science, merely the explanation of the observation. Often scientific explanations change as more data (observations) are collected.
maybe the reason permaculturists don’t define things carefully is that they’d end up wasting 2 thirds of an article on finding a satisfactory definition when the term dynamic accumulator seems pretty obvious: anything you use to dynamically accumulate nutrients.
i was raised by scientists but i still think there is a time and place for accuracy and another time and place for observing the world around you and acting on whatever you notice. sorry if you find that confusing or ‘fluffy’.
There is certainly time for both. But what do you do when your observations are in direct opposition to science?
The problem with your definition is that it’s stripped out the central point of why the term exists. The idea of a dynamic accumulator is that you’re gathering nutrients that wouldn’t be available to the rest of your plants. If you’re pulling readily-available nutrients out of the top levels of the soil and then composting the accumulators to put them back in, you’re just wasting time. If there’s no such thing as a dynamic accumulator in this sense, that’s fine, but redefining it this way seems to be like saying, “since there’s no such thing as a unicorn so let’s redefine it to be a horse.”
1) provide a reference of your definition.
2) Provide a reference to support you claim that they “gathering nutrients that wouldn’t be available to the rest of your plants”.
First off, I found this a very reasonable assessment of the dynamic accumulator controversy. I do, however, take issue with one statement.
You say, “The whole permaculture ‘thing’ is a very squishy, non-scientific, affair.”
Why the hate for permaculture? I think it is unreasonable to call a movement based on the observation and emulation of nature “very squishy” and “non-scientific,” when the root of science is the observation and analysis of natural phenomenon.
At best, you could question the methodology of permaculture because it rarely uses controls in its test. However, one could argue that modern industrial agriculture is one giant control group.
The reason for the statement is that almost none on the ideas that are specific to permaculture are supported by science. And the proponents of the method seem to shy away from doing proper testing. Show me one report that includes published references to support their position.
other groups tend to adopt permaculture methods once they notice they work.
Would you call a plant such as this a chelator plant, or is that type of bonding different?
There is no such thing as a chelator plant. Chelation is a type of chemical bonding that takes place between two molecules. So you can have a molecule that chelates certain other molecules or ions, but the concept can not be applied to a plant.
I’ve never thought that Dynamic Accumulators give any benefit over other plants. Sure all plants will take something different or different quantities of nutrients out of the soil but what normally happens is a plant with a big thick root is singled out because it goes deep. After reading http://soilandhealth.org/wp-content/uploads/01aglibrary/010139fieldcroproots/010139ch9.html I realised that a lot of plants can put roots down 3 or 5 feet and more so many many plants can pull nutrients up from way down and make available near the surface.
Robert! Absolutely love your comments!
Here – Pittsburgh area – they plant a lot of plants to help clean the destroyed soils of the old steel and chemical plants… However, I’ve yet to witness them removing any plant material! They brag about how the plants will clean it all up – but, anyone with even my half a brain knows one has to remove those plants! Although, once removed, I wouldn’t be shocked if they wouldn’t just dump it as (fill) material at the local dumps…
Shame, isn’t it?
If the pollution is due to heavy metals then the plants must be removed to have any effect. For pollution due to organic contaminants, you do not need to remove the plants.
You pick very interesting topics! I may now mulch with Moringa since I have three trees. Can’t wait for the next post! Thank you!
I use Dynamic Acculators each and every Fall!
Tree Leaves!
I call them Dynamic because their roots grow deep… (well, except the roots that grow on my lawn surface… That I trip over…)
Wonder what Washington and Jefferson called their mix of Doo and leaves?
Even trees do not have deep roots that are very effective for retrieving nutrients. But leaves are good in the garden.
Robert goes where others fear to tread!
Your piece is very well argued. It is a lovely idea that plants mine deep nutrients – I have talked about it myself. When you think about it deep in the ground any subsoil/sand/rock is a very infertile place and clay particles are likely to hold far less nutrients than those fully charged with plant nutrients at the surface.
Some gardeners imagine substantial nutrients can be extracted from rock. Not so unless you have a few thousand years
It is also quite fascinating how plants can extract metals as you quote. I understand arial photography of vegetation can detect metals brought up a very long way
What is deep soil like? it may be devoid of nutrients, but maybe since roots rarely go there, there is a lot of nutrients? If rock is continually decomposing then nutrients might accumulate.
It is also true that nutrients slowly leach from upper layers to lower layers. Even Potassium, which moves very slowly, does move and eventually pollutes water ways.
But I suspect you are correct. Most nutrients will be in the upper layers, especially in soil that has a good organic layer which allows microbes to continually recycle nutrients.
Here is an interesting question. If plants can accumulate heavy metals – are any of the vegetables doing this? Wouldn’t it be funny if we find out spinach is a lead accumulator?
No, that would not be funny I eat a lot of spinach and I do not like to think that I have been eating lead
Another thought: when plants accumulate heavy metals what happens to those metals when the plant dies
Over time the plants decompose and the heavy metals are returned back to the soil. Remediation only works if the plant material is removed from the site and treated to extract the heavy metals.