Pallets are an attractive option for raised bed construction due to their affordability and availability. Often found discarded behind stores, at the dump, or sold cheaply, pallets provide a sustainable alternative to buying new lumber. Additionally, re-purposing pallets aligns with the principles of recycling and reducing waste which is never a bad idea to consider. Constructing raised beds from pallets can also add a rustic, charming aesthetic to your garden.
However, before you rush to build your raised beds from pallets, it's essential to understand the risks, especially when it comes to the treatment of the wood.
Pallets are designed for transporting goods, and as such, they are often treated to prevent the spread of pests and diseases across borders. The type of treatment a pallet has undergone is typically indicated by a series of markings found on the pallet's side. These markings provide crucial information that determines whether the pallet is safe for use in a garden, where the wood will come into contact with soil and plants. Keep in mind that a pallet may have one or a combination of these markings.
Pallets at the end of their lives, usually when gardeners acquire them, are often unmarked or in poor enough condition that markings or evidence of treatment are not obvious.
Here's a breakdown of the most common markings you may encounter:
The IPPC Logo. The IPPC (International Plant Protection Convention) logo is the most common marking found on pallets. It resembles a small tree symbol with an outline and is a part of the global standardization for wood packaging materials. This logo indicates that the pallet meets international shipping standards and has undergone treatment to prevent the spread of pests.
HT Pallets marked with an “HT” have been heat-treated. This process is popular in Canada and the United States. It involves heating the wood to a specific temperature for a set period, which kills any pests like fungi, or insects that might be present in the wood. Soft wood pallets are heated to a core temperature of 132°f, and 140°f for hard wood if you're interested. Importantly, no chemicals are used in this process, making HT pallets generally safe for garden use.
DB The “DB” marking indicates that the pallet wood has been debarked, meaning the bark was scraped off of the wood before it was milled. Debarking is not a treatment method but rather a process that makes the wood easier to work with and less susceptible to pests. Debarking has no effect on the chemical properties of the wood and as such is generally safe to use for lumber.
KD “KD” stands for kiln-dried, which is a process where the wood is dried in a kiln to reduce moisture content down to at least 19% or below. Kiln-drying helps prevent warping and splitting but does not indicate whether the wood has been treated with chemicals. Kiln-drying temperatures don't necessarily reach up to the level of heat treatments and so it isn't really considered a treatment for pest control. It's not uncommon to see code “KD-HT” indicating kiln-drying and heat treatment with both processes accomplishing something different. KD pallets are safe to use in gardening.
MB This is one that you want to watch out for! If you see the letters “MB” on a pallet, it indicates that the wood was treated with methyl bromide, a toxic chemical fumigant used to kill pests. Methyl bromide is a highly effective pesticide, but it's also toxic to both plants and animals. Pallets treated with this chemical should never be used in gardening, as the chemical residues can leach into the soil and be absorbed by plants, posing serious health risks to humans and animals. You will often see “MB” paired with other treatments like “DB-MB” meaning debarked and treated with methyl bromide, or “KD-MB” for kiln-dried and treated with methyl bromide for example.
Using chemically treated wood in your garden can lead to the contamination of your soil, which in turn can affect the health of your plants and pose risks to anyone consuming the produce. The leaching of toxic substances like methyl bromide can have long-term effects on soil quality, potentially rendering it unusable for safe food production.
While the IPPC logo and the accompanying treatment codes are the most common markings on pallets, you may also encounter regional markings or codes that provide additional information. For example, some pallets might include a country code (e.g., “US” for the United States) or a manufacturer's identification code. These additional markings can help trace the origin of the pallet, but they don't usually impact its safety for garden use.
It's important to note that some pallets, especially those used for domestic purposes or in certain industries, may not have any markings at all. There are still unmarked CCA-treated pallets circulating about, and you don't want to use them in your garden. In these cases, it may be best to err on the side of caution and avoid using the pallet for gardening unless you can confirm the pallet's provenance and treatments, if any. (That's unlikely.)
Markings or not, it's wise to check any pallet you intend to use for any signs of spills, stains, or unusual odors that might indicate contamination from the materials it previously carried. And some contaminants are colorless and odorless.
Using pallets as lumber for raised bed gardening is a sustainable and economical option, but it requires careful consideration of the wood treatment. Understanding pallet markings is essential to ensure the safety of your garden and the health of your plants. Always prioritize heat-treated (HT) pallets, avoid those marked with methyl bromide (MB), and thoroughly inspect any pallets before use.
If you are at all in doubt about your pallets' source or past, it's safest to use them for applications that do not involve edible crops. They can also be recycled! Inyo County Residents can take them to the Bishop or Big Pine drop offs. Mono County residents should contact their Solid Waste Department.
Keep in mind wood from pallets that are not chemically treated may not be long-lasting in the garden due to the moisture. Be prepared to maintain them as the boards wear out.
With the right precautions, pallet wood could be a valuable resource for your garden, contributing to a productive and environmentally growing space.