Dynamic Nutrient Accumulators
Dynamic accumulators are plants that are particularly effective in gathering certain plant nutrients. They may have deep tap roots that allow them to access nutrients from deeper soil levels that other plants cannot reach and draw them up to the surface, for example. These plants can then be used as mulch, to make compost, or in organic liquid plant feed. While this is an area of permaculture practice where more research is needed, evidence is growing that the use of plants that can gather certain nutrients and store them in high concentration in a bioavailable form in their plant tissues can help maintain thriving systems.
Permaculture is, at times, a somewhat confusing blend of informal anecdotes and the scientific method. Many permaculture teachers and practitioners use terms in ways that, unfortunately, can be rather imprecise (and I certainly include myself in their number at times).
In the attempt to transmit hope and positive ideas for the future of humanity on this planet, extremely complex ideas can be turned into simple soundbites which, though they may inspire people to action, don't always have the science-based vigor we may desire.
'Dynamic accumulators' is a term that is extremely commonly used in permaculture circles. And yet, sadly, it is often not particularly clearly defined, nor rooted in genuine scientific knowledge.
Statements are often passed off as fact when describing the use of these in permaculture systems, drawing a veil over the fact that until recently, we have known very little about them in scientific terms. And far more research still needs to be done into this fascinating topic.
However, just because a term is not always clearly defined, and even when there is still research to be done, this does not mean that the term relates to pseudo-science.
Far from it. In fact, the more we learn about dynamic accumulators, the more permaculture practitioners are confirmed to have been correct, at the very least, about the principle of their use.
We just have to recognize that this field is still, relatively speaking, in its infancy. And we should bear this in mind as we seek to find the right plants for our permaculture systems.
What are Dynamic Accumulators?
The term dynamic accumulator is often used loosely in permaculture to refer to plants that are particularly good at gathering certain nutrients.
Often certain plants are chosen because they have deep roots that are said to seek out nutrients other plants cannot reach. But plants typically will receive most of the nutrients they obtain through the higher levels of soil in any case – so root form is not truly the factor that defines these plants.
However, we may often choose plants with deep tap roots when choosing companions – in a fruit tree guild for example – because competition with more shallow-rooted species may be reduced. And even when deeper-rooted plants get a lot of their nutrients from shallower roots, any that they do retrieve from lower horizons still helps to keep those nutrients within the system.
The key idea, however, when talking about dynamic accumulators is that these plants are particularly good at gathering particular nutrients and storing them in their plant tissues in a more bioavailable form.
The broad idea within permaculture is that dynamic accumulator plants show promise as a closed-loop solution for nutrient management, and that they can be used as chop and drop mulches, in composting, and for liquid plant feed within our growing systems.
The idea is that these plants gather particular nutrients into their plant tissues (fairly well confirmed), which we are then able to return to the soil for the benefit of other plants (less well confirmed).
Until fairly recently, many claims made were largely backed up only be anecdotal evidence and informal research. While these things certainly have some value, there was certainly a need for a more rigorous application of the term, and for a more rigorous scientific method with regard to the use of dynamic accumulator plants.
The Science Behind Dynamic Accumulation
At face value, the broad concept makes sense – in scientific as well as vaguer terms. We have a wide body of peer-reviewed research that shows the accumulation of beneficial nutrients in the context of cover cropping in agriculture, and the benefits derived by following crops.
And hyperaccumulation of metals in certain plants has been extensively studied for over 40 years. Since, in this related field, we are talking about the same processes, if not the same applications, we can learn from this field to gain more information about our own.
The primary problem is that clear criterion for dynamic accumulator plants had not been established in the same way as they had for hyperaccumulators (of heavy metals), and the term was not clearly defined.
All that is now, however, is finally, beginning to change. As interest in sustainable growing solutions increases, scientific communities are increasingly seeking to validate concepts that sustainable permaculture practitioners have long suspected to be true, but often lacked the ability to help to prove in ways that satisfy scientific minds.
Research into Dynamic Accumulators
Recent research is beginning, just beginning, to add a scientific basis to this common permaculture idea.
Excitingly, a farm in New York, in spring 2022, reached the end of a SARE-funded research project seeking to establish clear criteria for the identification of dynamic accumulator species and investigate potential applications for these plants.
First of all, Dr Duke's phytochemical and ethnobotanical databases were used to compile peer-reviewed nutrient concentration data across thousands of plant species. Concentration averages were calculated across 20 beneficial nutrients and dynamic accumulator thresholds were set at roughly 200% the average.
In total, 340 species were found that have been shown to achieve nutrient concentrations high enough to quality as dynamic accumulators adhering to the set thresholds. You can see a list of these species in this Dynamic accumulator database and USDA analysis.
This provides a basis from which to grow a database as more information from peer-reviewed sources emerges and nutrient concentrations and averages change over time. And a framework from which further studies can be undertaken.
The second part of the study involved the selection of 6 promising species from this database for two years of trials at Unadilla Community Farm. The full report on the field trials can be found here.
It is especially interesting to me that stinging nettles were shown to perform well in the on-farm trials, since I have also found stinging nettles to be beneficial in my own forest garden, both chopped and dropped and used as mulch, and when used as a liquid feed.
This trial goes some way to confirming my belief that this dynamic accumulator (a common 'weed; where I live), enriches the topsoil by taking nutrients from lower soil horizons and that it has a high nutrient carryover rate.
This study is particularly useful because, although this is just the beginning, it provides help and suggested frameworks for further research moving forwards.
One of the most important things to remember when thinking about how and where to use dynamic accumulator plants is that these plants cannot add nutrients to a soil, only gather those that are already present.
As the recent study showed, “plant tissue concentrations are relative to soil nutrient concentrations. Dynamic accumulators are well suited to extract specific nutrients from fertile soil, but they are not going to create nutrition that isn't there.”
This is very important to remember. Since it reminds us that dynamic accumulators are only one of a number of approaches that must be taken to maintain a healthy soil – and soil health once again comes front and centre.
However, in this study, both lambsquarters and comfrey (two other plants I find to be useful in my own garden) surpassed dynamic accumulator thresholds even in poor, unamended soil. (Both for potassium and the latter for silicon too.)
Though just one study, the research discussed above does help to begin the journey towards putting on a more scientific footing the permaculture belief that by utilizing plants that are known to accumulate specific nutrients, we can selectively draw up nutrients that are present in the soil.
I am not a scientist, but I will be fascinated to discover more about dynamic accumulators and their uses and will keep a close eye on new science-based information as it emerges in this fledgling field.
Another fascinating area of research that has a bearing on the use of dynamic accumulators relates to the soil, and the microbial life it contains – mycorrhizae, and soil bacteria, for instance.
The role that microorganisms play in the transmission of nutrients between living plants, and the breakdown of organic matter, is another area where much more research is required. This too may have important information to tell us about how dynamic accumulators might best be used within a system.
Many people are astonished to learn how little we actually know about plant interaction, and what goes on below the soil. Science has made leaps and bounds in recent years, but there is a huge amount about the natural world and its connectivity that we are yet to discover or fully understand.
How Dynamic Accumulator Plants are Used in Permaculture Systems
As science progresses, it will help us understand the mechanisms behind some common permaculture practices. It will help us see where anecdote and informal experimentation have served us well and put us on the right track, and where beliefs are not as well-founded.
In the meantime, however, in the absence of clear confirmatory evidence for or against the benefits of certain practices, we must fall back on the methods that so many of us feel are so efficacious in our gardens and growing systems – learning from our own results to determine the best practices for our own properties over time.
So, let's take a look at some common ways in which dynamic accumulator plants are used in permaculture systems (whether the claims and anecdotal results are scientifically verifiable or not):
I have comfrey, nettles, docks, sorrel ,borage and more within my forest garden, as part of a strategy to ensure ongoing fertility, as well as certain nitrogen fixing plants that may or may not quality as dynamic accumulators too.
I tend to use these and other 'dynamic accumulators' within chop and drop systems, for composting, and in liquid plant feeds. However, these plants all serve many other functions as well, however, so their dynamic accumulation is not the only reason to grow them.
Chop and Drop Systems
Plants referred to as dynamic accumulators are often used within chop and drop systems, as materials that are cut once or several times in a year and then dropped on the soil surface as mulch.
One of the desired aims is to return the nutrients these plants contain to the soil where they can be taken up by other plants – either those growing at the same time, or subsequently.
However, the process also serves other functions, helping to increase soil carbon, improve soil structure, conserve soil moisture, suppress weed growth and protect the soil surface. So it can be difficult to isolate one benefit from the others when trying to determine whether plants that we might designate as dynamic accumulators are more beneficial than any others.
The mulch might be laid in the area where the plants are growing, to shortcut natural cycles and with the goal or retaining nutrients within the system. Such as in a food forest, for example.
Or it might also be transferred to a different growing area, where it can help to add nutrients and improve the soil. Often, dynamic accumulators are grown in marginal areas, and cut for use as mulch in annual growing zones.
Dynamic accumulators are also added to composting systems with the goal of improving the NPK nutrient content of the mix, speeding decomposition, or with other specific purposes, such as addressing certain deficiencies in pot plant mixes, for example.
While I cannot speak to the details of decomposition and nutrient release and availability, it is the case that certain plants commonly used as dynamic accumulators in permaculture systems generate large quantities of biomass relatively quickly, which can be useful where compost generation, especially at scale, is required.
Liquid Plant Feeds
Dynamic accumulators are also used to create organic liquid plant feeds. I use nettles to make a nettle plant feed, and also comfrey to make 'comfrey tea' both of which I personally find to promote healthy growth and improve yields in my annual vegetable garden.
These three practices are all often common parts of permaculture practice – but we must remember that while we may often see excellent results, we know far less about 'dynamic accumulators' plants and the soil than you might think.