Definition
Dynamic accumulators are those plants that extract and gather nutrients ‒ specifically inorganic minerals ‒ from the soil or air and make them available to other plants, or indeed to animals, or to us.
Background
Dynamic accumulators are generally resilient and fast-growing plants with extensive root systems that draw nutrients from deep in the soil.
They thrive in a wide range of poor, unbalanced soil and in areas where topsoil has been lost, and they disperse easily.
Most dynamic accumulators would therefore be recognised as weeds.
In nature, dynamic accumulators are prevalent during the first stage of succession. Originally, this would have meant on land disturbed by ‘floods, fires, landslides, or receding glaciers’, but today this generally means on land disturbed by human activity, including mining, landclearing, farming, and other forms of cultivation.
One distinct type of dynamic accumulator is the nitrogen fixer, plants such as clover, lupines, and beans. These have a symbiotic relationship with a type of bacteria in the soil that allows them to capture atmospheric nitrogen and store it in the soil. Many dynamic accumulators that fix nitrogen from the air also access other minerals from the soil.
As is typical of weeds, ‘their ecological function is to restore damaged and disturbed ecosystems in order to prepare them for higher quality plants’.
As permaculturist Dave Jacke puts it:
The main thing is that the paradigm that we're using to describe invasive species has many faulty aspects. The thinking is being muddled by framing the issues incorrectly. If we don't see invasion as part of succession ecology then we are on the wrong track, folks. Because most plants that are considered invasive are disturbance adapted species.
Examples of dynamic accumulators
The attached table identifies many dynamic accumulators. This draws on US sources, so some plants listed would not grow as readily or function as efficiently here. It also features a significant but still selective list of possible minerals. The dynamic accumulator potential of prominent local weeds is something to keep researching ‒ CSIRO research, for example, has explored the capacity of capeweed to accumulate cadmium and zinc.
Despite this US bias, many plants that flourish locally and that are already familiar as beneficial within permaculture systems and/or organic gardening practices are listed. These include common garden herbs such as camomile, fennel, parsley and peppermint; recognised medicinal plants such as dandelion, nettles and plantain; compost activators such as borage, comfrey, and yarrow; green manure favourites such as clover; and common lawn or pasture weeds such as dock.
How they work
The extensive root systems of dynamic accumulators both catch nutrients that would otherwise leach away, and access and assimilate soil nutrients in mineral form. As plants die back, the plants decompose to return nutrient-rich organic matter in an accessible form to the soil.
In addition to accumulating nutrients and making them available to other plants, the weedy habit of these plants offers many other benefits in improving soil. The roots leave tiny channels through the soil that aid ‘the exchange of gases, the percolation of water, and the movement of worms and bacteria’, which greatly enhances soil structure.
They shade the soil, moderating extremes of temperature and moisture from which bare soil suffers, enhancing soil life, improving water retention, assisting soil stability and helping prevent soil erosion.
They can be helpful in indicating existing soil deficiencies, in that naturally growing dynamic accumulators point to the deficient minerals or nutrients that these special plants are accessing, either from the air (the classic ‘nitrogen-fixing’ plants such as clovers) or the soil. (The mineral the plant accumulates will be what it is generally lacking.)
Alternatively, if a deficiency is identified through soil testing, dynamic accumulators can be encouraged or introduced to help address that specific deficiency.
Other garden benefits
Among dynamic accumulators, many offer other specific benefits to soil, or have other uses.
Plants with long tap roots, such as dandelion and dock, are very helpful to break up heavy clay soils and aid against compaction.
The roots of a cover crop and the decomposing foliage of green manures such as Mexican marigold (Tagetes rinuta), ornamental marigolds (to a lesser degree), and the crotolaria legumes exude chemicals that help suppress soil nematodes that can harm other plants.
A tall-growing plant can be used to shade out other (less beneficial) weedy plants, while a broad-leafed plant can be used to smother them.
The flowers of some dynamic accumulators provide food for bees, particularly valuable in those that flower at times when other pollen and nectar sources are scarce, such as capeweed, dandelion and oxalis.
Others attract or harbour other pollinators and worthwhile insects such as ladybugs.
Other uses
There is a reasonably good chance that weeds will be edible, because they have evolved to focus on creating new plants rather than defending themselves with protective toxins, and indeed many dynamic accumulators have become, or can be used as, food, either for animals or for people. As the young, tender shoots/leaves tend to be the most palatable, picking these for food or making them available as fodder can be an effective control technique.
Their ability to harness minerals can be particularly useful to supplement dietary mineral deficiencies, including providing iron-rich greens for those of us with low iron levels (a common concern for vegetarians, particularly).
Some have specific medicinal uses.
How to use dynamic accumulators in the garden
Dynamic accumulators can be used in a number of ways:
- as a cover crop, grown before or between other plantings
- as a green manure, turned into the soil where they have been growing
- as a mulch, pulled or cut back and used as a surface mulch around other plants
- as compost, pulled or cut back and added to a compost heap or other composting system
- as companion plants, interplanted with, or planted near, desired plants
Tilling after green manuring will bring seeds to the surface to germinate, so be carefeul to follow promptly with seeding or transplanting of desired plants.
A cover crop or green manure similar to the intended crop may harbour pests. So avoid, for example, a cover crop of mustards that can allow the cabbage root maggot to flourish.
Be careful of letting weeds go wild, especially if you live in the suburbs or in other areas where there are weed control laws. Attractive weeds can be chosen in these cases, and weeds kept clipped or otherwise controlled.
Be aware of possible risk to or undesirable competition with native species. When planting non-native dynamic accumulators, always check to make sure they are not invasive in your area.
Be careful about inadvertently encouraging unwanted proliferation. For example, oxalis corms will stay active in soil that is moved or composted, and comfrey will regrow from disturbed roots or root fragments.
Some weeds, such as dandelion and nettle, can produce allergic reactions.
Glossary
‘catch cropping’ earlier term for ‘cover cropping’ in that it catches leached nutrients
‘cover cropping’ leaving dynamic accumulators growing
‘dynamic accumulators’ plants that extract and gather nutrients ‒ specifically inorganic minerals ‒ from the soil and make them available to other plants,
‘green manuring’ turning the dynamic accumulators into the soil
‘lasagne gardening’ see ‘sheet mulching’
‘no dig gardening’ adding layers of organic matter onto undug soil to create a garden bed, with planting directly into the mulch.
‘resident vegetation’ alternate term for weeds
‘sheet mulching’ using a surface mulch such as carpet, newspaper or black plastic to keep a bed in darkness except where plants emerge.
Sources
Kerry G, ‘How to improve heavy clay soil naturally’, eHow.com, http://www.ehow.com/how_4713086_improve-heavy-clay-soil-naturally.html#ixzz0wWz4XvFj accessed 14 August 2010
Kerry G, ‘Dynamic Accumulators for Better Soil’ http://hubpages.com/hub/Dynamic-Accumulators-for-Better-Soil accessed 14 August 2010
R. Hamon, J. Wundke, M. McLaughlin and R. Naidu, ‘Availability of zinc and cadmium to different plant species’ http://www.publish.csiro.au/paper/S97052.htm accessed 14 August 2010
Terri Johnson, ‘Dandelion – King of Dynamic Accumulators’ Roots of Healthy Living http://rootsofhealthyliving.com/dandelion-king-of-dynamic-accumulators/ accessed 14 August 2010
Robert Kourik, ‘Grow your own Fertilizers’, from Designing and Maintaining Your Edible Landscape Naturally, by Robert Kourik. Metamorphic Press, 1986. reprinted with permission on http://www.earthworksboston.org/replicate/A_Grow_Fertilizer.htm accessed 14 August 2010
‘Cam and Jess’s Urban retreat’, http://permaculture.org.au/2009/11/10/letters-from-melbourne-cam-and-jesses-urban-retreat/ accessed August 14
‘Compost Tea Organic Farming and Liquid Organic Farming Fertilizers for Organic Gardening’ http://www.small-farm-permaculture-and-sustainable-living.com/compost_tea_organic_farming_and.html accessed August 14
‘Dynamic Accumulators of Nutrients for Composting’ http://www.oregonbd.org/Class/accum.htm accessed 14 August 2010
‘Improving Your Soil’ http://www.autonopedia.org/garden_and_farm/Soil_Compost_And_Mulches/Improving_Your_Soil.html accessed August 14
‘Resident Vegetation’ http://www.sarep.ucdavis.edu/cgi-bin/CCrop.exe/show_crop_32 accessed August 14
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