Dynamic Accumulators – Are They Beneficial to the Garden?

Dynamic accumulators are plants that accumulate higher than average nutrients in their leaves. Some people grow these plants and then either mulch with them or compost them so that these extra nutrients are made available to other plants. This is particularly popular in permaculture circles, but it is also used a lot in organic gardening.

On the surface this sounds like a great idea. Use plants to fertilize your other plants. How can you get more organic than this.

In this post I will look at the pros and cons of using dynamic accumulators to try and understand how beneficial they are to gardens.  In the process I’ll also uncover some myths about dynamic accumulators.

Dynamic Accumulators – What Are They?

I have answered this question is some detail in the post entitled Dynamic Accumulators – Do They Exist?. In summary:

“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.” (ref 1)

Many people believe that these extra nutrients are retrieved from deep in the soil due to long tap roots – I will discuss this myth in more detail below.

Gardeners grow dynamic accumulators so that they can harvest the leaves and either use them as mulch or compost them. Both options return the leaves and their nutrients to the soil where other plants can make use of them.

The fundamental notion of dynamic accumulators is that they retrieve nutrients from soil which are not readily available to the average plant. By harvesting them a gardener is able to make these nutrients more available to all plants.

Lets look at some fundamental flaws in this concept.

The Myth of Deep Roots

There is no doubt that some plants have deeper roots than other plants.

Proponents of dynamic accumulators would have you believe that these deep roots are used to mine nutrients from deep in the ground. There is no scientific evidence to support this idea.

Robert Kourik, the author of Understanding Roots, had this to say in a recent discussion on The Garden Professor Facebook Group, “…. some plants are more efficient at absorbing some nutrients compared to others. Is this due, as many gardeners assume, to deep roots or is it due to more efficient accumulation at surface soils. This remains a grossly unresearched dynamic.”

Plants that have deep roots, like comfrey, have most of their roots in the top foot of soil. It is much more likely that accumulator plants get the majority of their nutrients from their largest root mass rather than their deepest root.

The top layer of soil is the most fertile. It is the place where you find organic matter that is continually decomposing and releasing nutrients. It is also the place where you find most microbes which also contribute to higher nutrient levels.

At this point, there is no support for the idea that deep rooted plants retrieve the majority of their nutrients from low levels in the soil. It is much more likely that they get their nutrients from the same soil level as all other plants. Accumulators are just more efficient at picking up and retaining certain nutrients.

Nitrogen Fixing Accumulators

One group of dynamic accumulators are the legumes which are able, with the help of bacteria, to fix nitrogen gas from the air. These plants are accumulators for nitrogen.

Legumes do not form large tap roots. Instead they make use of a shallow root system to gather their nutrients.

Dedicated Space

One of the problems with the concept of using dynamic accumulators to feed other plants is that you need to dedicate space to grow them. That might  work if you have a mini one acre farm, but it certainly does not work well in most backyards. For most gardeners space is at a premium. Why not grow more tomato plants and skip the accumulators?

Dynamic Accumulators as Mulch

Mulching beds is one of the best things you can do for your garden. Taking the leaves from dynamic accumulators and using them as mulch makes some sense. Why bother composting them first, when they will decompose nicely as a mulch layer.

Fundamentally this makes sense, but I don’t know how easy it is in practice. The leaves will dry quickly, shrink in size and reduce the mulch layer in very short order. You are then left with either adding more mulch or living with bare soil and weeds. The alternative is to use wood chips in flower/shrub gardens and straw in vegetable gardens. These mulches also add nutrients to the soil, improve soil structure, but last a season or more.

If you do want to mulch with dynamic accumulators I would suggest laying them over top of another mulch material. That way you maintain a thick mulch layer and get the nutrient benefits of the accumulators.

Fast vs Slow Feed

Adding organic material onto beds is a great idea. The problem with doing this is that you have to accept the fact that this is a slow feed for your plants. The leaves of the dynamic accumulators will decompose slowly over time. There is nothing wrong with that unless you need a fast feed in something like a vegetable garden. If your vegetables need nutrients now there is no point in laying down leaves only to have the nutrients released months or years later.

A slow steady feed is better in the long run, but the user needs to be aware of this limitation.

To combat this problem some people take the leaves and turn them into smoothies in a blender. They work under the misguided belief that by chopping things up into a green syrup the nutrients are made available right away. They are wrong. Most of the nutrients are tied up in large molecules and a blender does not change this. Granted a smoothy will decompose faster than whole leaves but it will still take time.

Do Dynamic Accumulators Make Plants Grow Better?

Virtually all of the talk about dynamic accumulators involves opinions and theories. Is there real proof that plants grow better if they are mulched with dynamic accumulators? Will compost made from dynamic accumulators make plants grow better than with regular compost?

Clearly any organic matter will add nutrients and make things grow better – no one doubts that. Organic matter will also improve soil structure – we can accept that as well.

But how do dynamic accumulators compare to traditional forms of organic matter? Do they perform better than manure? Or regular compost? It might surprise you that this question has not been studied. When I did a Google Scholar search for studies on dynamic accumulators I did not find a single one. Scientists don’t really put much faith in the idea of dynamic accumulators and permaculturists tend not to perform proper scientific studies which are publishable in peer reviewed journals.

If you know of such a study, please add the link or reference in the comments below.

There seems to be no scientific evidence that dynamic accumulators are any better or worse than other forms of organic matter.

Solving Nutrient Deficiencies

It is assumed by proponents of dynamic accumulators that the accumulators can solve nutrient deficiencies in the soil.

As already discussed deep roots are not going to be very helpful at solving nutrient deficiencies.

Accumulators are more efficient than regular plants at retrieving certain nutrients. But what happens to these nutrients once they are added back to the soil in the form of mulch or compost? The assumption is that the nutrients are now available to other plants – but is this really true?

To understand this better we need to ask an important question. Why was there a deficiency in the first place?

The deficiency might be due to the fact that the nutrient in question just does not exist or it exists at very low levels. In this case it is unlikely the accumulators will be able to absorb much of it. Just because an dynamic accumulator will absorb a lot of a given nutrient in good soil does not mean it can do so in soil that is mostly devoid of the nutrient.

A second possibility is that the nutrient is in the soil, but is not available. For example, soil can have good levels of iron, but in alkaline soil the iron gets tied up and is unavailable to plants. Maybe accumulators are better able to pull iron from soil even in alkaline conditions.

What happens when this iron is returned back to soil? Since the soil is still alkaline, it will again become tightly held by the soil. There is no reason to think that it suddenly becomes available to other plants.

If the dynamic accumulator gets the nutrients from the same soil level of other plants, it is unlikely that they will solve a nutrient deficiency. One exception to this would be a case where the dynamic accumulator is grown in an area where the soil has plenty of nutrients and is then moved to an area where there is a deficiency.

One Dynamic Accumulator is Not Enough

Each dynamic accumulator plant is good at storing high levels of one or a couple of nutrients. Just because they are good at one nutrient does not mean they are good at storing all nutrients. People who believe in dynamic accumulators study each plant and come up with a mixture of plants that will provide the nutrients they need.

Mike H. in One Thing Leads to Another had a look at dynamic accumulators and used Dr. James Duke’s Phytochemical and Ethnobotanical Databases  to develop a spreadsheet of dynamic accumulators showing the amount of nutrients they accumulate. Using such lists, proponents are able to select a few plants to provide the wide spectrum of nutrients they need.

Sounds like a lot of extra work and garden space.

Toxic Dynamic Accumulators

Look at any list of dynamic accumulator and it might tell you which nutrients the various plants actually accumulate. The above mentioned spreadsheet is one example. You will notice that the list only shows elements that are good for plants. It does not show toxic elements like heavy metals.

Phytoaccumulators are plants that are especially good at retrieving and storing heavy metals. These plants are used for cleaning up polluted sites.

There is a good chance that a plant which is good at retrieving nutrients like iron, magnesium and zinc is also good at retrieving heavy metals like lead, and chromium.

It is quite possible that the dynamic accumulators you use are adding both beneficial nutrients and toxic heavy metals to your soil. Without testing for heavy metals you have no idea what you are adding.

https://www.gardenmyths.com/comfrey-dynamic-accumulator/

Dynamic Accumulators – Are They Useful in the Garden?

The idea of accumulating nutrients from deep in the soil is not supported by science. Growing the plants in the same location as they will be used will not add benefits to the garden. Growing them in one spot to mine the nutrients and then moving them to your garden will add nutrients to your garden, but this is also true of moving manure or compost to your garden.

There is no scientific evidence that using dynamic accumulators is any better or worse than using other forms of organic material. From an environmental point of view you might be able to argue that using waste organic material such as manure or compost is a better option since you are not wasting land to make fertilizer.

Mulching and composting are both good for the garden. Using dynamic accumulators for this is one option, but I am not convinced that the evidence supports the idea that they are better than other options.

References:

1. Dynamic Accumulators – Do They Exist? ; https://www.gardenmyths.com/dynamic-accumulators-exist/
2. Comfrey – Organic fertilizer and mineral Accumulator; https://www.youtube.com/watch?v=HqjW4EtUCe8
3. Photo Source; Takashi .M