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Tips for the Compleat Gardener: Phytoremediation goes on


As the climate changes and we are forced to adapt we find we are looking to Mother Nature for help more and more. She is giving sun and wind to keep our energy flowing, food to sustain us and even cleaning up our messes and her own.

As the sea rises there are communities that are routinely flooded by the ocean when tides are high, homes are going up on stilts, the land hosting salt-loving plants. Nature has sent barley and sugar beets to remove the salt from the soil after the flood.

We have lessened our use of lead in most products, paint and fuel for two, but it remains heavily in our soils everywhere civilization has been.

In the spring fields of wild mustard are a common sight in the Northeast at least, bright yellow haze of Braissica juncea pulling the lead out of the soil as it delights the eye and the butterfly. The seeds become the brown mustard condiment.

Later in the season the plant responsible for a lot of hay fever attacks ragweed (Ambrosia artemissifolia) with her friend dogbane take over lead removal. I always think it ironic that the plant causing so many sniffles has a first name, ambrosia, used to describe the food of the gods, that could impart immortality. Capocynum cannabinum which is also known as dog hemp, has long been used as fiber to make rope and fabric. It does contain a toxic sap that can cause skin irritation and is commonly found on the wild edges of gardens and in natural places.

It hosts a few pollinators and sucks the lead out of the soil. One must harvest and incinerate the plants to retrieve the metals taken out of the land.

More plants are being created through biogenics to have phytoremediatory uses to deal with mercury, selenium and PCBs. The aforementioned poplar trees can remove selenium and mercury using phytovolitilization through which process contaminants are removed from the soil, transformed by biomolecules such as glucose and amino acids to alter the compounds and decrease toxicity. The new compounds are breathed out by the tree.

Cannas use a process called phytodegradation or phytotransformation the results of which are chemical modification of environmental substances using the plant’s metabolism. A row of staid-looking cannas can render pesticides, solvents, explosives and industrial chemicals non-toxic using micro-organisms in the roots to metabolize and change.

It would be great to see mass plantings of cannas where flooding has occurred; in warmer than zone six areas they don’t even have to be dug up for winter storage.

Phytostimulation is the process of enhancing the soil by providing the microbes living in the rhizosphere around plant roots nutrients to enhance their ability to break down and digest petroleum hydrocarbons, PCBs and PAHs.

Salix osier viminalis, also called the “basket willow” and Brassica hapus (rapeseed) are good at getting rid of petroleum hydrocarbons, MTCE, organic solvents as well as several heavy metals.

Many of the chemical abbreviations are showing up in news stories as we hear of more and more polluted areas and these plants are hard-working plants that can move in and help ameliorate the problem.

It is true that the smaller, annual phytoremediators can’t go very deep in the soil but the shrubs like the spreading osier willow, other willows and poplars can help at a deeper level. More to come.