Within the world of Permaculture we often find reference to plants known as Dynamic Accumulators. In brief, this is the idea that certain 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. When the leaves fall in autumn and winter and are broken down, those stored nutrients are then incorporated into the upper layers of the soil where other plants will benefit from their deposition.
As a physician, I strive for scientific accuracy. I understand the scientific method and the world of academia. I know, beyond doubt, the benefit this arena has provided for the world. However, I also know, beyond doubt, that there is a lot of truth that has not been proven in a lab. This may be due to many factors. To name but a few: the topic has not yet been studied, there are flaws in the design of the study, or the topic is too complex for reductionist evaluation.
So with our scientific minds turned on, let’s examine the concept of dynamic accumulators.
We will start with the scientific evidence… Unfortunately, there is not much. In fact, I can find almost no research into dynamic accumulators. Strike that. I can find NO research into this concept at all. None. Many sources site references, but these references just don’t pan out. There are circular references, there are references to non-existing sources, and there are references to (just being honest) less than reputable books or authors. My lack of results was a bit disappointing.
As it turns out, it appears that the concept of dynamic accumulators has been passed down and around for so long that it has been accepted as fact. This concept did not originate with Permaculture, but it has been adopted and advocated by it for a long time. So much so, that many people associate dynamic accumulators with Permaculture.
Well then, how did this concept of dynamic accumulators get started? Where did it originate?
Although he didn’t develop the concept, I think we can safely blame Robert Kourik, organic gardening/landscaping author for bringing the term “dynamic accumulators” to the forefront of our minds. In 1986, he wrote Designing and Maintaining Your Edible Landscape—Naturally. On page 269, he created a list of “dynamic accumulators”. This list was compiled from a number of sources including: Weeds: Guardians of the Soil (Joseph Cocannouer), Practical Organic Gardening (Ben Easey), Stalking the Healthful Herbs (Euell Gibbons), Weeds as Indicators of Soil Conditions (Stuart Hill and Jennifer Ramsay), Weeds and What They Tell (Ehrenfried Pfeiffer), and The Organic Method Primer (Bargyla & Gylver Rateaver).
This list of plants was a good-faith attempt to provide guidance about what gardeners were throwing into their compost piles. Robert Kourik now openly admits that he regrets including that list in his book. He realized that the list was mainly based on informal and anecdotal reports, but this realization came too late. Pandora’s box was opened. Since then, many authors have shared the information from this chart (I am guilty as well!). Some authors added additional information based on even more informal or anecdotal information. We can now find reputable authors sharing these “scientific facts” with trusting readers.
I have had informal communications with both Toby Hemenway (author of the fabulous Gaia’s Garnden and upcoming book on urban Permaculture) and Dave Jacke (author of the highly recommended Edible Forest Gardens and upcoming book on Coppice Agroforestry). They both feel that the dynamic accumulator charts listed in their books were, at a minimum, unnecessary and unsubstantiated additions to their work.
With all this said, what evidence do we actually have about this idea of dynamic accumulators?
We do know that some plants accumulate minerals in high concentrations in their tissues. In the botanical community, this concept is known as “phytoaccumulation” or “hyperaccumulation”, and this has been very well researched. These plants are able to grow in soils with high concentrations of certain minerals. Researchers are using hyperaccumulating plants in areas that have been contaminated with heavy metals or high-value metals. The plants pull out (phytoextract) these minerals from the soil. The plants are then harvested and processed to extract the minerals from plants to be recycled or dealt with in a more ecological manner. This “phyomining” has been used, with success, on significantly contaminated sites.
In addition, there has been an extensive database put together by botanist James “Jim” A. Duke Ph.D. which provides information on thousands of plants. Specifically, and for our purposes, the database provides information on the concentration of minerals found in the tissues of plants. His Phytochemical and Ethnobotanical Database is hosted on the USDA ARS site (United States Department of Agriculture, Agriculture Research Service). This is a wealth of information that would take a long, long time to fully peruse and appreciate. Using the information from Dr. Duke’s database, a free, downloadable Nutrient Content Spreadsheet was created. I am not sure who created it, but I found it on Build-A-Soil.com. This is well organized spreadsheet with multiple worksheets (pages).
With this information, can we connect the dots for dynamic accumulators?
For instance, according to Dr. Duke’s database, we can see the phosphorus (P) concentration in Lambsquarter (Chenopodium album) is over 36,000 ppm (parts per million). This is a high concentration. Therefore, it would make sense to grow Lambsquarter on our site. We would let the Lambsquarter die back in the winter and compost in place. By spring, we should have higher concentrations of phosphorus (P) in our soil. Right?
Unfortunately, while this scenario sounds good, we have no proof that it will work. Our logical pathway sounds plausible, but the reality is that nature is never quite as simple as we would like. First, minerals don’t appear out of nowhere (alchemy is still not science!); if the soil or subsoil has no phosphorus to begin with, then the Lambsquarter cannot accumulate it. Second, if the soil has no biology (i.e. Dr. Elaine Ingham’s Soil Food Web), then there is a good chance the phosphorus may not be bioavailable to the roots. Third, while our scenario sounds good, we have no scientific proof (research data) that if the Lamsquarter did accumulate phosphorus it would indeed be returned to the soil in a usable form to future plants. Maybe it will, but would it take six months, one year, five years, or twenty-five years to become available again? This is information that we just do not have.
In addition, we cannot use anecdotal reports about dynamic accumulators. People will often site their own garden as “proof”. Unfortunately, this anecdotal information is not scientific evidence. I am not saying that their soils did not improve with the planting of dynamic accumulators, but was it the dynamic accumulation or another factor that caused the improvements? Was it mulching, composting in place, biomass accumulation, biodiversity, microclimate creation/enhancement, etc.?
As a good friend of mine likes to say, “The plural of anecdote is not data.” But, to be my own devil’s advocate, it is the repeated anecdotal report that often leads to scientific research which eventually “proves” a long-held concept to be true. For example, almost a year ago on this site Ben Stallings shared his experience using comfrey to improve his soil. This article is a great example of single data point that should spur more research.
Unfortunately, high-quality research is both time and money intensive.
What then should we do with the concept of dynamic accumulators?
Take the information for what it is, soft data. We can make some logical assumptions, i.e. “guesses”, and hope for the best. But we should not treat or teach the concept, the theory, of dynamic accumulators as scientifically proven information. We should not treat it as fact. We should definitely not rely solely on dynamic accumulation as our single solution for degraded soils. Of course, if we are appropriately applying and practicing Permaculture, we wouldn’t do this anyway.
Personally, I will continue to use dynamic accumulators in a holistic approach to soil improvement. It may help our soils for our intended purposes in exactly the way that we think, or it may help for entirely another reason. If it works, I don’t really need to know why. Having more diversity on our sites will almost always be of benefit… scientifically proven or not.