The use of traditional railroad ties for building raised garden beds is a controversial practice generally advised against by environmental and health experts. A railroad tie, or sleeper, is a heavy piece of timber used to support railway tracks. While the size and durability of these timbers are appealing for garden construction, the preservation method introduces significant chemical hazards. The primary concern is that toxic chemical treatments applied to the wood can leach into the surrounding environment, posing a risk when growing food crops.
Why Treated Ties Pose a Risk
The primary preservative used to treat most traditional railroad ties is coal-tar creosote, which is classified as a restricted-use pesticide by regulatory bodies. Creosote is a complex mixture distilled from coal tar, containing hundreds of different compounds. Among these compounds are polycyclic aromatic hydrocarbons (PAHs), which are the source of the environmental concerns.
Many PAHs, such as benzo(a)pyrene, are known or suspected carcinogens. These chemicals are highly persistent and do not easily break down in the environment. The leaching process is exacerbated by garden conditions, especially the presence of moisture and warmer temperatures.
As water and heat interact with the wood, the creosote slowly migrates out of the tie and into the adjacent soil. Studies have shown that the concentration of PAHs in the soil is highest immediately next to the timber, often exceeding safe residential limits for a distance of up to 18 inches. When food crops are grown in this contaminated soil, they can potentially take up these compounds.
Research has demonstrated that various plants, including root vegetables like radish and leafy crops, can accumulate PAHs from creosote-contaminated soil. The presence of these substances in the soil creates a direct pathway for human exposure through consumption. Direct contact with the contaminated soil also poses a risk, particularly for children. The regulatory label for creosote-treated wood specifically warns against using it in residential settings where it may come into frequent or prolonged contact with skin.
Identifying and Safely Handling Old Ties
Railroad ties treated with creosote have distinct characteristics allowing for their identification, even years after installation. The most obvious sign is a strong, pungent, and acrid odor from the coal tar chemicals. Visually, treated ties typically appear very dark brown or black, often with an oily or greasy surface residue.
If ties are already in place or must be moved, specific safety precautions are necessary to minimize personal exposure. Direct contact with the wood should be avoided by wearing chemically impervious gloves and long-sleeved clothing. If the wood must be cut, sawing generates dust and fumes containing the chemical preservative.
Cutting or sanding must be done in a well-ventilated area while wearing eye protection and a respirator to avoid inhaling contaminated particles. Treated wood should never be burned, as the smoke releases highly toxic compounds into the air. Disposal of used railroad ties is not simple, as they are considered special or hazardous waste in many municipalities and cannot be placed with regular household trash.
Recommended Safe Materials for Raised Beds
Several safe and effective materials are available for constructing raised garden beds that eliminate the risk of chemical leaching. These options ensure that the soil remains clean and the produce grown is safe for consumption.
Untreated wood is a popular choice, with naturally rot-resistant species like cedar and redwood being excellent options. These woods offer durability without chemical preservatives, meaning they will not leach toxins into the garden soil.
Other safe alternatives include:
- Stone, brick, or concrete blocks, which are inert, highly durable, and will not break down to release contaminants.
- Metal panels, such as galvanized steel or specialized corrugated steel, which are non-leaching.
- Composite decking, typically made from recycled plastic and wood fibers, which provides a long-lasting, weather-resistant solution.
- Repurposed materials like food-grade plastic containers or specialized fabric grow bags, offering simple and inexpensive alternatives.