Phytoextraction is the act of using plants to remove toxins from soil. Instead of using chemicals or removing the dirt you plant certain kinds of plants or mushrooms that either absorb the toxins or neutralize them. The process can take longer since you may have to wait out several growing seasons. But if you have the time it is by far the cheapest way. And it is arguably a lot more ecological since you are using natures way, you aren’t lugging large amounts of soil around, and you aren’t using chemicals.
In Brooklyn we have many gardens with high heavy metal counts. The arsenic from the pressure treated wood, the lead from the sanded paint, the mercury, cobalt, nickel, chromium etc from god knows where.
The phytoextraction soil remediation plan for these gardens would be to plant things like sunflowers, for example. Sunflowers according to some sources (not all) help extract lead.
Phytoextraction is a good strategy if the situation is not an immediate threat. If you don’t have children running around in the soil, if you aren’t eating vegetables from it, if you aren’t spending a lot of time digging in the soil, then why not plant some things back there that will do their magic over time. You are doing good for the world.
But if the situation needs imediate attention and you can’t wait for the growing process to take care of it then you may have to do some more drastic soil remediation such as removing the soil and/or mixing it with lime and organic mater.
Here are some great resources to learn more about Phytoextraction.