Pressure-treated lumber, while widely known for being able to withstand the elements and often lasting decades instead of only a few years, is not the best choice for a raised bed, especially if that bed is being used to grow edibles. Chemicals used to treat the wood may leach into your soil and be taken up by plants. Women who are pregnant or nursing and children especially should not be exposed to pressure-treated wood.
Wood that has been pressure-treated is much more durable. It has undergone a process where it is subjected to several chemicals at high pressures so that they are driven deep inside the wood, preserving it and helping it resist decay. Many of the compounds used in this process, such as creosote, pentachloropophenol and inorganic arsenicals, have been classified as pesticides and have the potential to cause harm to human and animal health. Arsenic, a common compound used, is poisonous in large doses.
Use in the Garden
Using pressure-treated wood as opposed to untreated wood raises your risk of being exposed to these chemicals. When buried in the soil to make a raised bed, the compounds slowly leach into it and are taken up by plants. They can also come into contact with the surfaces of fruits or vegetables that you will then take inside to eat.
Sawing and Handling
If you are going to use pressure-treated lumber, keep in mind safety precautions. Any time you handle the lumber, wash your hands thoroughly afterward. Keep children and pets away from the area. If you need to saw the wood in order to obtain the correct dimensions, do so on a windless day, outdoors, where you can minimize your inhalation and the particles won’t carry. Wear gloves and long sleeves. Clean up thoroughly and launder the clothes you wore separately.
Especially when growing edibles, it is safer to use a non-treated alternative. Children are particularly sensitive to chemicals since they are still developing and should not be exposed to pressure-treated lumber. Although many types of wood don’t last long in the moist garden environment, some choices for raised beds are better than others. Cedar and redwood lumber, for instance, are naturally rot-resistant. Brick and stone also make good raised beds.