5 Raised Bed Materials You Should Never Use
Whether you plan to grow food or flowers in raised garden beds, it's wise to avoid materials that can leach toxins into the soil.

Heavy metals and other chemicals can accumulate in the soil near raised beds, but they can also spread beyond the confines of the garden. Toxic pollutants are most mobile in clay, sandy, or moist soils and end up in the water table.

The first rule of gardening really should be: do no harm. Here are some of the worst raised bed materials that can have serious environmental impacts:

pressure treated wood

Before 2004, chromated copper arsenate (CCA) was the most widely used wood preservative. Discontinued due to concerns over arsenic exposure, Alkaline Copper Quaternary Ammonium (ACQ) is the standard wood treatment today.

Although it is far less toxic than its predecessor, ACQ contains large amounts of copper, which can leach into the surrounding soil.

Copper is highly toxic to fish and aquatic life, and using ACQ pressure-treated wood to contain wet soils increases the likelihood of copper leaching into watersheds.

MB tray

Wooden pallets can be an inexpensive and waste-free way to make a bed—but watch out for those marked "MB."

Methyl bromide is a broad-spectrum insecticide, which is extremely harmful to human health. It is not recommended to use treated wood in any way.

It easily kills fungi, insects, roundworms, and even rodents. MB trays emit exhaust gases into the atmosphere, directly destroying the ozone layer.

In any DIY pallet project, indoor or outdoor, use only "HT" printed or heat-treated pallets. This means that the trays are sanitized at 132°F and above for at least 30 minutes. The HT Tray can be completely safely upgraded to a loft bed and beyond.

railway relations

Wooden railroad ties are treated with creosote, another powerful pesticide that is strictly prohibited around humans and plants.

Creosote is a soot that repels termites, fungi, and other pests. It is made from tar from coal, petroleum, and other fossil fuels.

Prolonged and frequent exposure to creosote railroad ties is not only harmful to human health, it can leach into the soil and cause damage to plants, insects and small animals.

cinder blocks

Cinder blocks made from fly ash or coal particles contain arsenic, lead, mercury and other heavy metals. While cinder blocks haven't been mass-produced in about 50 years, if you're making a raised bed out of recycled materials, you might want to avoid them altogether.

Modern concrete blocks look identical to old cinder blocks, but are made of Portland cement and other aggregates. Concrete is considered non-toxic and safe for garden use. However, the concrete industry has a huge carbon footprint and is one of the major sources of CO2 emissions globally.

used tires

Efforts to upcycle trash into something useful are indeed admirable, but some items—such as used tires—are usually best avoided in the garden.

Tires contain harmful substances such as cadmium and lead, which can theoretically seep into the soil. Some believe that old tires release most of their toxins during their first year on the road and take decades to degrade.

But the jury is still out on the issue. To date, no scientific studies have been conducted to determine whether old tires contaminate garden soil. But why take the risk? Especially when growing food using raised beds, it's better to be safe than sorry.

Once your raised beds are built and ready, the next thing you need to do is fill them with rich, healthy soil.