Arsenic: One of the best hyper accumulators of arsenic in the soil and in ground water (from treated wood) is the pteris vittata, a Brake fern that sucks arsenic from the soil at an amazing rate. This fern can also be grown hydroponically to cleanse water sources. The fronds should be cut in the fall and disposed of safely. Brassicas, particularly Indian mustard, are also hyper accumulators of arsenic and other metals, if you need a sunny patch cleared up. 

Leachate: The nasty liquid that percolates from landfill areas can be safely contained and controlled by rapidly growing poplars. These poplars then exhale them as gasses into the air, and transform them. They are short lived, however, so it is advisable to plant longer living trees, like mulberry and Osage orange, amongst them. They are capable of breaking down some of the most toxic and persistent poisons, including PCB's. Got a new house on an old landfill? Start planting. 

Benzene: Alfalfa grass and poplar trees can remove not only benzene compounds, but also ethyl benzene and other chemical compounds from the soil. Again, cut the grass and dispose of it the first year.

Heavy Metals: Plants can't do much about the music, but the actual metals in your soil, like zinc and cadmium can be absorbed by Alpine Pennycress and cabbage. For those of you who are thinking that these beneficial plants are looking distressingly like a lot of weeds, take heart. The Pelargonium Geranium is also a hyper accumulator of heavy metals, and are excellent at treating CCA (chromium, copper, arsenic treated woods…you know…your deck?), and lead in soils, including the lead that is in gasoline. Sunflowers are also a heavy metal accumulator, so you can have your cheery garden while healing the soil.

Radiation: Okay, so this isn't your average problem with soil in a garden. But folks who live in the desert near where testing has occurred can find that their soil has suffered fallout and contains radioactive materials.

Pigweed (amaranthus retroflexum), though it may seem to be just another noxious weed, can remove radioactive cesium from the soil. In a heavily contaminated area, pigweed can remove three percent of the cesium in three months. In a lightly contaminated garden, it could clean it up in one or two growing seasons, planted two or three times a season. And here is where sunflowers shine again, as lovely plants with a purpose. They are used to absorb cesium and strontium from soils.

Petroleum: Picture this…your husband or teenage son has been working on your car, changing the oil. The pan is left in the way a little to long, and WHOOPS! Into the garden or yard it goes. Not a good scene. But never fear! Fescue and Bermuda grass, clover and alfalfa can stabilize that oil and keep it from killing off the garden. The microbes used to inoculate the clover and alfalfa are better at stabilizing it faster than the other grasses, but either will work. One season should do the trick, and you can go back to planting there next year.

Explosives: Okay, well, again, this is not a problem for most folks, unless, like my family, they have some hicks in the woodpile that went fishing with dynamite when they were young, drunk and stupid. Or maybe you have a kid who is into the whole evil genius scene. In any case, if you have TNT, RDX or any of the other explosives chemicals in your property, parrot feather, reed canary grass, water star grass, and elodea could be your answer.

Nitrates: This is not generally a problem in soils, but in water, nitrates can build up and cause problems. Nature has given us the right idea where water is concerned. She filters her waters through bogs and marshes, slowly easing the water through a myriad of roots, leaves and stems to make sure that what flows into the sea can be assimilated by the life already there. Plants such as bulrushes, water lilies, arrowhead, cattail, sweet flag, and water hyacinths can absorb the extra nitrates along with moderate amounts of heavy metals and even chlorine to cleanse the water and make it safe for wildlife and humans alike.