If you have soil that's been contaminated by lead, you know that it's probably not safe for vegetable gardening and it can also be a hazard to children and pets who play on your property.
Many homeowners install raised garden beds and bring in new soil and compost to try to solve the problem, but you can also use plants to naturally remove the lead from the soil.
The process of using plants to remove toxins from the soil or to render them harmless is called phytoremediation.
Some plants are so effective at phytoremediation that they can be smelted after being used to clean up water-soluble metals at extremely contaminated sites and the metals can be extracted back from the plants.
The USDA explains how one plant physiologist is using plants to clean up soil:
Kochian's cost-effective "green" technology uses plants to "vacuum" heavy metals from the soil through their roots. He says, "Certain plant species—known as metal hyperaccumulators—have the ability to extract elements from the soil and concentrate them in the easily harvested plant stems, shoots, and leaves.
Different plants are best suited for removing different toxins, as well.
It is important to note that these plants may not remove all of the toxins from soil in one growing season. Lead tends to remain in soil for a very long time, which makes it harder to remove from your soil. Factors such as the rate of growth of the plant and the amount of lead in your soil will influence how long it takes to fully clean up a site.
A heavily contaminated industrial site can take up to 14 years to fully remove all traces of lead with phytoremediation. If your soil is heavily contaminated, be sure to grow edible crops in raised containers until tests show that lead levels are safe.
That said, phytoremediation is an excellent, natural, low-cost way to detoxify your land -- especially if your property has only mild to moderate contamination.
Click on the photos to view seven of the best plants for removing lead from your soil, and learn more about each one.
Remember not to eat or compost plants that you grow to remove toxins from your soil! Be sure to dispose of these plants properly after removing them, or you'll simply relocate the lead to another part of your yard (or worse, your body).
Stay tuned in this column for upcoming articles highlighting plants that will remove other toxins, such as arsenic, pesticides, uranium and mercury.
Sunflowers are among the best plants for phytoremediation of lead and other toxins.
The common sunflower has been the subject of numerous studies and is used to extract heavy metals and toxins including Lead, Uranium, Strontium, Cesium, Chromium, Cadmium, Copper, Magnesium, Nickel, and Zinc.
Sunflowers are easy to grow and can add beauty to your yard as you're detoxifying it. Be sure to remove the entire sunflower plant (roots and all) after each growing season.
Ornamental cabbage and all members of the cabbage family are excellent at phytoremediation.
In one study in Maine, cabbage was used for phytoremediation of a heavily contaminated industrial site. After the completion of the field trial, phytoremediation was successful in reducing the total soil lead level from an average of 984 mg/kg in the surface soil (0-15 cm) to 644 mg/kg. This was in just one growing season.
Ornamental cabbages are easy to grow and make large, tidy bedding plants that can even be used to create living flower borders instead of blocks or fencing. Ornamental cabbage will happily grow through hard frosts and can then be removed at the end of fall.
If you do not have heavy lead contamination and merely want to use plants to remove any small amounts, these annuals can be planted between garden rows to help detox your soil and keep weeds down.
Be sure to dispose of the plants properly. Do not allow them to overwinter and break down, where they will deposit the lead back into your soil.
Wheat, corn and other grains
Wheat, corn and other grains can also be very effective at removing lead from the soil.
Other grasses and grains that can be effective at phytoremediation of lead include tapegrass, Highland bent grass and rapeseed (canola).
It is important to be sure to dispose of the grains properly and not consume any edible crops that are grown to remove lead from the soil, however.
Sea pink thrift is a lovely garden plant that can help clean your soil while adding beauty to your landscaping.
Thrift is a popular perennial garden flower that does well in gardens designed as xeriscapes or rock gardens.
Thrift is a compact plant that is easy to grow in dry, sandy and even salty soil. It is also extremely tolerant of copper contamination.
While nobody is about to recommend planting ragweed for any reason (especially if you live in a residential area and care about keeping your neighbors happy), here is one reason not to be too upset if you can't eradicate it all off of your property.
Ragweed is considered by many to be the single best plant that exists for removing lead from contaminated soil.
The common ragweed, Ambrosia artemisiifolia, is the most efficient plant to remove lead from the ground.
This great page also lists so many great uses of ragweed that you might not hate it quite so much, at least when it's not allergy season.
Furthermore, ragweed is so effective at removing lead from soil that at least one patent has been filed to use ragweed for this purpose.
Mustard greens are such good plants for phytorediation that some organic farmers are experimenting with using them to turn polluted land into community gardens.
WPXI.com reports on one collaboration between a local grad student and a property owner who wants to start a community garden on her polluted land:
"We hope to grow food, specifically for the community -- fresh local organic food at affordable prices," Graziani said.
She turned over a section of her property to English so she could experiment with a natural way to cleanse the soil using mustard greens.
"Mustard greens are considered hyperaccumulators. By natural process, they draw toxins out of the soil, accumulating it in shoots and roots." English said.
Duckweed is a great solution if you have a wetland area that's got lead contamination.
Duckweeds, or water lens, are flowering aquatic plants which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands.
Wikipedia further notes how effective duckweed is at purifying wetlands in other ways:
The plants can provide nitrate removal, if cropped, and the duckweeds are important in the process of bioremediation because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen and phosphates. For these reasons they are touted as water purifiers of untapped value.
The Swiss Department of Water and Sanitation in Developing Countries, SANDEC, associated with the Swiss Federal Institute for Environmental Science and Technology, asserts that as well as the food and agricultural values, duckweed also may be used for waste water treatment to capture toxins and for odor control, and, that if a mat of duckweed is maintained during harvesting for removal of the toxins captured thereby, it prevents the development of algae and controls the breeding of mosquitoes...
These plants also may play a role in conservation of water because a cover of duckweed will reduce evaporation of water when compared to the rate of a similar size water body with a clear surface.