Saturday, October 29, 2016

Plants That Build Healthy Soils

Good, fertile soil is a must for any garden, even a forest garden. But did you know that some plants can help build healthy soils? 

Dynamic Accumulators, Nitrogen Fixers, and Hyperaccumulators

Some plants are known as dynamic accumulators, because  they grow very deep roots that bring up minerals from deep down, making them available to more shallow-rooted plants. Some plants are also nitrogen fixers, called that because their roots partner with rhizobial bacteria (this a form of mutualism in biological terms), which causes a nitrogen boost in the soil.

Dynamic accumulators and nitrogen fixers can be grown near other plants (companion planting), which is why they work so well in forest gardening,  or as a form of ground cover crop and "green manure." Your choice of specific plants to use will depend upon your particular location and climate, of course, but partial lists of both appear below.

Additionally, plants known as hyperaccumulators can be used to detoxify contaminated soils by removing certain heavy metals and other toxic elements, such as lead, mercury, arsenic, and aluminum. This is a process known as phytoremediation. A phytomediation table matching the toxic elements with their hyperaccumulator can be found on wikipedia. 

Partial List of Dynamic Accumulators (along with their use in Forest Gardening)

Black Locust - Robinia pseudoacacia - Canopy
Dogwoods - Cornus sp. - Understory
Arrowroot - Maranta arundinacea - Herbaceous Layer
Borage - Borago officinalis - Herbaceous Layer
Comfrey - Symphytum uplandicum - Herbaceous Layer
Dandelions - Taraxacum sp. - Herbaceous Layer

Indian Grass - Sorghastrum nutans - Herbaceous Layer
Lemon Balm - Melissa officinalis - Herbaceous Layer
Mint - Mentha sp. - Herbaceous Layer
Stinging Nettle - Urtica dioica - Herbaceous Layer

Switchgrass - Panicum virgatumHerbaceous Layer
Yarrow - Achillea millefolium - Herbaceous Layer
Plantains - Musa musa - Herbaceous Layer
Alfalfa - Medicago sativa - Herbaceous Layer

Partial List of Nitrogen Fixers* (along with their use in Forest Gardening)

Alder tree and shrubs - Alnus sp. - Canopy or Understory
Black Locust - Robinia pseudoacacia - Canopy
Kentucky Coffee Tree - Gymnocladus Dioicus - Canopy

Russian Olive - Elaeagnus angustifolia - Understory
Bayberry - Myrica sp. - Understory
Acacias - Acacia sp. - Canopy or Understory

Most Beans - Fabaceae family - Herbaceous Layer
Peanuts - Arachis hypogaea - Herbaceous Layer
Vetches - Vicia sp. - Herbaceous Layer
Perennial Clover - Trifolium sp. - Herbaceous Layer
False Indigo - Baptisia australis - Herbaceous Layer
Scarlet Runner Bean - Phaseolus coccineus - Vine
Wisteria - Wisteria floribunda - Vine

* Among the best known and most readily available nitrogen fixers are those in the legume family - Fabaceae. This family includes most beans, clover, alfalfa, buckwheat and peanuts.


Plants For A Future - Informative website and database listing over 7000 edible, medicinal, and otherwise useful plants.

Introduction to Forest Gardening - a very useful introduction to the concept of forest gardening for those unfamiliar with it.

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