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Can Raised Beds Make It Safer to Grow Vegetables over Contaminated Soil?

5 October 2018 by Eugene Kelley

Growing your own fruits and vegetables is one of the most popular trends for renters and homeowners alike, but many newcomers to gardening aren't aware of potential health risks lurking in the soil. Planting fruits and vegetables in contaminated soil could allow your plants to absorb lead, heavy metals, pesticide or herbicide residues, and carcinogenic petroleum byproducts. Soil around a home is easily contaminated by hundreds of different causes. Thankfully, using a raised bed kit can help you grow safe and healthy plants regardless of soil quality.

Understanding Soil Contamination

Flakes of lead paint that fall into the soil, residues deposited by car exhaust, chemical dumping of old paint and petroleum products, and even leaking heat oil or septic tanks can all contaminate the soil around a house. Only a soil test that specifically checks for the most common contaminants will reveal if your ground layer is safe to plant in or potentially dangerous. A quality test will also determine if contaminant levels are low, and relatively risk-free, or high enough to cause concern.

Using Solid Barriers

For best results, the bottom of a raised bed should be sealed with a solid barrier like landscaping fabric to stop plant roots from reaching the contaminated layer of soil. Make sure the barrier is not waterproof so the plants don't die of excess moisture, but avoid perforated or loosely woven materials since roots can easily reach through the openings. This also prevents the soil you add to the raised bed from breaking down and mingling with the layer of dirt below, making it harder to tell where the contamination starts.

Slowly Improving Contaminated Soil 

Building a raised bed over a contaminated patch of soil helps prevent both short and long term risks. Covering the soil with a bed prevents children and pets from digging in the soil, which is a primary way that toxins and contaminants transfer from the ground to the body. Adding fresh soil and compost increases microbial activity, and testing shows that increasing soil diversity speeds along the breakdown of most major contaminants. There's no need to mix together the new and old soil to get these benefits since the tiny microbes and bacteria travel freely between the two, even with a layer of landscape fabric at the bottom of the bed. Stirring or turning contaminated soil increases the release of toxins into the air for you and your family to absorb, so putting a raised bed over a problem patch is your best option.

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