Start landscaping with a clean slate

By G. Owen Yost

The main approach used to clean up polluted earth (digging up the offending soil and hauling it to the landfill) is costly and disruptive. Nationally, the cost of using these common methods is over $700 billion. As we try to find cheaper, more sensible ways to clean up polluted soil, professionals are looking at a new tool: plants. Hundreds of species of plants represent the botanical equivalent of detox centers: They absorb polluting molecules. This may divulge methods that could be used by individual homeowners.

Your soil may become polluted with repeated use (and misuse) of chemical fertilizers, insecticides and herbicides. Pollution can also come from spills of things like paint or used motor oil. Commercially available products can certainly help, but can be expensive.

One limitation of eliminating pollution by using plants is that care must be taken to prevent birds and other wildlife from eating plants that have accumulated high concentrations of toxic materials. But perhaps the biggest limitation is that plants take time to grow and work, with several crops over months or successive seasons needed.

Much remains unknown about just how they do what they do. But with a growing list of successful projects, the method has shown its worth ? even if the precise chemical processes remain a mystery. What is known is that plants evolved with very efficient mechanisms for pulling necessary nutrients, water and minerals out of the ground. Plants can?t run around hunting for food, so they must harvest it from the soil they?re in. The more effectively a plant does this, the more likely it is to thrive and reproduce. For example, the combined lengths of the roots of a single sunflower plant could total many miles.

Just as botanists have been scouring the plant world for promising drugs, now they are seeking particular species that have the ability to target polluted soil. From Ecuador to the Hudson River Valley, constructed wetlands with plants are already cleaning up pollution from landfills, slaughterhouses, cider mills, sewage plants, fish farms and parking lots. One of the most established techniques is using trees, mostly poplars and willows, to treat groundwater from aquifers contaminated with solvents or other toxic organic compounds.

The latest discovery came at a central Florida lumberyard where the ground was badly contaminated with arsenic compounds from wood preservatives. Arsenic is so toxic to most plants that it is an ingredient in some herbicides. But after scientists at the University of Florida tested 14 plant species growing there, they found that the brake fern, common in the Southeast and other parts of the world, had arsenic in its fronds and stems at more than 200 times the concentration in the soil. The fern is now being sold to filter the poisons out of water. This seems very timely since the current administration is allowing increased levels of arsenic in drinking water.

Going with the trend of gene alteration, poplars have been grown with a gene taken from bacteria that transform a toxic form of mercury into a safer one. Last June, research described in the Proceedings of the National Academy of Sciences successfully inserted into tobacco plants a gene that breaks down a variety of toxic organic chemicals.

As of now, this knowledge has little impact on the typical home landscape ? just on large, heavily polluted areas. But the time will come when you?ll be able to buy a few plants to clean up your chemically polluted soil. In fact, there are products on the market now that "cleanse" home landscapes that have been polluted by chemical fertilizers, herbicides and insecticides. So if you want to start landscaping without artificial chemicals, you can start the season with a clean slate.

Owen Yost is an area landscape architect specializing in designing low-maintenance landscapes while incorporating native plants with hardscape. He is a member of the American Society of Landscape Architects, Keep Denton Beautiful and the Native Plant Society of Texas. His Denton office is at 4516 Coyote Point; call 940-382-2099 or 940-383-9655 or e-mail him at Yost87@charter.net