Phytoremediation: Using Plants to Clean Contaminated Soil

After a "Garden Mythbuster" article on rubber mulch leaching heavy metals, readers asked how to remediate such soil. Phytoremediation—using plants to extract, degrade, or stabilize pollutants—offers a low-cost, natural solution, especially for urban sites with limited cleanup budgets.

How It Works

Certain plants tolerate and accumulate heavy metals (zinc, cadmium, nickel, lead, aluminum, mercury, chromium) in roots, stems, or leaves. They can transform toxins into less harmful compounds or release them as gases via transpiration. Tree roots reach deeper contamination than herbaceous plants. Best for low-to-moderate pollution levels. Pre-study ensures plants don't release harmful gases.

Common Garden Plants That Remediate

• Hydrangeas – extract aluminum (affects flower color).
• Melastoma affine (Blue Tongue) – aluminum accumulator; purple flowers, sweet blue-staining fruit.
• Brassicas (kale, mustard greens, collards, broccoli) – remove lead. Do not eat plants used for remediation.
• Water Hyssop – lead, mercury, cadmium, chromium in wetlands; ground cover with white flowers.
• Water Hyacinth – absorbs cadmium, chromium, mercury, lead, zinc, cesium, strontium-90, uranium, pesticides from water. Fast-growing, lavender-pink flowers. Invasive in frost-free areas.

Urban Gardening Context

As cities revitalize, new gardens often occupy formerly contaminated lots. If soil tests reveal pollution, phytoremediation is a viable, eco-friendly alternative to excavation. Contact your county extension office for region-specific plant recommendations.