Sunflowers as lead remediators
Despite much anecdotal evidence over the years, research shows that sunflowers and other plants have less of an effect on a more common urban soil contaminant: lead. Lead has a low solubility in soil, particularly when soil pH is high, and is therefore difficult to phyto-extract, but it is possible to make it less bio-available, using high quantities of organic matter as well as phosphate and iron-rich compost or fertilizers to, in effect, lock up the lead in the soil.
It is possible that many people that grow sunflowers and report a significant change in their soil lead levels are experiencing the lead-stabilization effects of amending their soil with phosphate-rich organic matter in their quest to give their sunflowers plenty of nutrients. Cultivation and tilling of that soil with amendments can also cover the top few inches of contaminated soil - effectively lessening the amount of airborne lead dust in the soil.
If you are dealing with suspected contaminated soil, the most important thing you can do first is to test it. Luckily, this is an easy process.
Getting a soil test
It’s always wise to have a professional test done in a new garden, but if you suspect lead or metals contamination, it’s essential. Comprehensive soil tests are available for a small testing fee in most states through the state’s cooperative extension service – sometimes metals contamination is even part of the basic lawn and garden soil test. If your state extension doesn’t provide this service, look to your neighboring states. Test results will not only give you an accurate idea of your soil health, but will usually suggest specific ways to up your soil fertility and balance your pH for common vegetables and ornamental plants.
Many of us don’t have the budget for full-scale dig & replace remediation – but we also may not be dealing with terribly toxic sites. If tests show that you’re dealing with a low contamination in your soil, don’t let the benefits of growing sunflowers and other crops be trumped by concerns over lead. Research shows that utilizing good growing and hygiene practices in your urban garden (particularly when children are involved) is usually enough to mitigate low levels of contamination.
Growing sunflowers and amending with hefty amounts of compost – thereby increasing soil phosphates – might be a safe and effective way over time to correct the problem. It is recommended that tests can be conducted annually over the course of several years, charting the progress that your soil makes.