Gardeners talk a lot about dynamic accumulators, and they are important for techniques such as permaculture and regenerative agriculture. The problem was that we didn’t have an accepted definition for them – nobody agreed on what they were.
The science of dynamic accumulators has recently advanced, and we now have a proper definition, an extensive database of possible candidates, as well as some research supporting claims about them. There is also new testing of weed teas made from them.
This may become more important to gardeners than you realize.
Key Takeaways
- We have an official definition for Dynamic Accumulators.
- About 10% of plants in the database qualify as dynamic accumulators for at least one nutrient. None qualify for all nutrients.
- Nutrients in weed tea are lower than most people expect.
A Definition for Dynamic Accumulators
In a previous post, called Dynamic Accumulators – Do They Exist?, I discussed the need for a definition for them and even proposed one of my own:
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.
A key point of this definition is the “10 times” section. We have to establish a limit.
Recent work by the USDA and other scientists has developed a new definition that may be adopted:
A dynamic accumulator is a plant that will absorb and retain, in any part of the plant, at least one nutrient at levels that are 2 times higher than the average plant.
Is the 2X value reasonable?
The 2X factor from the above definition, and my 10X factor, is arbitrary. Which one is more reasonable?
Let’s have a look at Russian comfrey as an example. It qualifies as an accumulator for potassium, producing 53,000 ppm potassium, based on dry weight, and it produces 2.8 lbs/sq ft (fresh weight). It contains about 85% water, so a sq ft produces 190 g dry weight, which can contain 10 g (2 tsp) potassium.
The average plant produces 4 g of potassium.
Is it worth growing comfrey to get an extra 6 g/sqft of growing space? Keep in mind that you also need to harvest and process it to use the potassium. Alternatively, you can grow an average plant that you want in that space and get 4 g.
Personally, I think 2X is too small to make dynamic accumulators a viable option for getting nutrients, but my 10X is probably too high.
The Dynamic Accumulator Database
A database of plants and their nutrient levels was developed using Dr. Duke’s phytochemical and ethnobotanical databases and made available to the public.
It contains nutrient data (ppm based on dry weight) for 350 plants, calculated from 7,000 data sets. It shows the results for 20 different nutrients along with a Dynamic Accumulator Threshold (ppm) for each one.
The database is continually updated as new data becomes available.
Summary of Observations:
- Every nutrient has at least one dynamic accumulator.
- On average, 10% of the plants qualify as dynamic accumulators for each nutrient.
- There are more accumulators for Ca, Cl, Fe, Mg, Mo, and S than for the other nutrients.
- Values for a given plant vary a lot based on the nutrient level used to grow that plant, resulting in significant variation for any given species.
That last point is critical to understand. A plant is only a dynamic accumulator if it is grown in soil rich in the nutrient in question. Dynamic accumulators do not exist in crappy soil.
Testing Dynamic Accumulators
As part of the project to create the database, a 2-year study was also done to test 5 specific plants to get a better understanding of the nutrient levels in the plant and compare them to the database.
| Test Plant | Accumulated Nutrients (previous studies) | Accumulated Nutrients (current study) |
|---|---|---|
| Amaranthus retroflexus (Redroot amaranth) | P, K, Ca, Fe, Mg, Zn | – |
| Chenopodium album (Lambsquarters) | P, K, Ca | K |
| Symphytum peregrinum (Russian comfrey) | K | K, Si |
| Taraxacum officinale (Dandelion) | B, Ca, Cl, Cu, Fe, Na, Zn | – |
| Trifolium pratense (Red clover) | Ca, Fe, Mg, Mn | – |
| Urtica dioica (Stinging nettle) | N, Ca, Mg, S | – |
The following are some of the key findings.
- Russian comfrey could be cut several times a season and produced the most plant growth (0.6-2.8 lbs/sq ft, fresh weight).
- The nutrients that are accumulated depend very much on the nutrients in the soil. “While capable of impressive nutrient concentrations when grown in the right conditions, results can vary considerably from site to site. This suggests that dynamic accumulators may be better suited for tying up excessive nutrients in rich soil, rather than extracting desirable nutrients from poorer soil”.
Is Comfrey a Dynamic Accumulator?
Comfrey is the dynamic accumulator that is mentioned most often. I discussed this question in another post before this new science became available. The data available at the time showed that it did not have any special high levels of nutrients.
The above-mentioned database includes Symphytum officinale, the common comfrey, which dynamically accumulates only cobalt and iron.
Russian comfrey (Symphytum peregrinum) is the one most people grow if they want a dynamic accumulator. Surprisingly, there is no entry for it in the database, showing how infrequently scientists analyzed it. That being the case, why do so many gardeners believe it is a great dynamic accumulator?
Weed Tea
Weed tea is a process where plant material is added to water, allowed to ferment for a few days, and then the liquid tea is used as fertilizer. The process is fully described in my post: Weed Tea, Fertilizer Tea – No Matter the Name, It Stinks
This test used rainwater with a pH of about 5.5 to make the tea. No agitation was used, and recorded temperatures ranged from 55.6°F to 84.9°F. The pH decreased during brewing due to the almost
immediate onset of fermentation.
Tea was made using 1 part fresh plant material to 10 parts water, in a 5-gallon pail. Samples were taken after 3 and 5 days of brewing.
- In most cases, the nutrient level was higher after 5 days than after 3 days, but this was not always the case.
- Cobalt, molybdenum, and nickel were detected at zero levels in the tea.
- Stinging nettle is a good accumulator for calcium, and it transfers a reasonable amount to teas.
| Test Plant | NPK |
|---|---|
| Amaranthus retroflexus (Redroot amaranth) | ? – 0.0057 – 0.076 |
| Chenopodium album (Lambsquarters) | ? – 0.0054 – 0.090 |
| Symphytum peregrinum (Russian comfrey) | ? – 0.0043 – 0.074 |
| Taraxacum officinale (Dandelion) | ? – 0.0055 – 0.059 |
| Trifolium pratense (Red clover) | ? – 0.0023 – 0.032 |
| Urtica dioica (Stinging nettle) | ? – 0.0089 – 0.060 |
| synthetic fertilizer (NPK ratio 3-1-2) mixed to 100 ppm nitrogen | 0.01 – 0.0033 – 0.0066 |
Many gardeners suggest diluting the tea because “it is very concentrated”, but the above data shows it is already at an appropriate level for use without dilution.
The brewing process does not raise the pH of the rainwater very much, which means that the fertilizer solution is also fairly acidic and may need to be neutralized before applying to plants, especially if brewed for more than 3 days.
Do Dynamic Accumulators Reduce Nutrients in Soil?
You would expect that nutrient levels in the soil would drop if plants are pulling a lot out of the soil, but that is not what happened. Soil tests after the above plant experiments showed that the nutrients in the soil increased, with the exception of sodium, which decreased.
This adds support for the argument in my post on Is Soil Fertility Decreasing? that suggests that our agricultural soil is not becoming nutrient-deficient.
The reason for this is that plants excrete a lot of chemicals into the soil to support their rhizosphere microbe populations. All of this microbial activity leads to further nutrient extraction from rock, making it plant available.
The Cut & Drop Method
The study also looked at the cut and drop method, which they call the chop & drop. In the cut & drop composting method, plant material is harvested and simply spread on the ground where natural decomposition takes place. The process adds nutrients more slowly, but it is easy to do.
This study did not see much of an effect from this method, but the material was only added in the final year of testing, so it is not a surprise that there was little change in soil nutrient levels.
Should You Use Dynamic Accumulators?
The purpose of using dynamic accumulators is to provide an organic source of nutrients. You grow the special plants, harvest them, and then apply them to the soil, which is low in the corresponding nutrients.
It is important to understand that no single plant is great at accumulating all the nutrients plants need. They are not general fertilizer plants. You have to select the ones that provide the nutrients you need in your soil, and use those.
But there is a catch with that. If your soil is missing a nutrient, growing a dynamic accumulator in that soil won’t retrieve much of that nutrient. They are only good accumulators if they are growing in soil that has the nutrient you are after.
This “catch” is even a bigger problem when you consider that you have no way of knowing the nutrient content of the plants you are growing, unless you are willing to do plant tissue testing. Without testing, you might go through the whole process of growing dynamic accumulators and spreading them in the garden without any real benefit.
Keep in mind that many of the dynamic accumulators are not desirable garden plants, so you need to dedicate some of your garden space to plants you would not normally grow. Is the time and space worth the effort?
If the plants only provide a 2X increase in the needed nutrient, then I don’t think they are a very good option for most gardeners. They are too complicated, take too much space and time, and don’t produce enough benefits.
I’m supposing that if the nutrient is not coming from the air, that growing the accumulator is only taking from the soil and then giving it back after it dies. The only advantage to us is if the plant has deep roots to that could bring the nutrients up to the surface for other shallow root plants to use.
Except for carbon, all the nutrients come from soil. When they die, nitrogen and sulfur can also be lost to the air.
The idea of deep roots gathering nutrients is a myth. Even plants with deep roots get most of their nutrients from the top few inches of soil.
Eventualy too, deeper you get into a subjective methode or soil biological stand point this is meaninfull to the observer as interpretation also. A root that dig that much, for instance considering alfalfa as plant of interest deploy meters down a complex root system to gather, exchange or release ”nutrients” from air or direct form within anareobic layers below. One take something from up to drop it down. As above so below stand for any dynamic inter-woven into life fabric. I can only speculate somekinda plants intelligence dig as such to get from this process a wider perspective and gain from this exchange more informations from nutrients, microbials life or gases release decays to assist others deeper down or upper up the rabit hole ie Humain, grazers and all that eat. Understanding stand as a personal opinion and wider we get from the business of payed by principals, the ground might possibly impart a different meaning then we observe from the NAKED I. I feel that interaction is finite subtle to much more then storage informations. We are about to live this all of us and the spectrum from these archaic process named science, sooner or later might just be laught at.