Treated lumber does leach chemicals, but in small amounts. In most cases, plants and people are nto at high risk for harm.
Q:
In your August 2000 issue (FG#74), an author suggested the use of pressure-treated lumber for raised beds. Don’t the chemicals that leach out of the wood damage and kill plants?
Joanne Gasperik, Lake Geneva, WI
A:
B. Rosie Lerner, extension consumer horticulturist at Purdue University in West Lafayette, Indiana, replies: Gardening in raised beds has become popular for many reasons. However, the controversy regarding chemical wood-preservation treatments has left many gardeners wondering about the safety of treated lumber.
Certainly, any discussion of potential toxicity must be undertaken with the knowledge that there can be great variability in sensitivity to pesticides in the environment. Keep in mind that toxicity is relative to dose and exposure. Some folks react to very low exposure to chemicals while others don’t react at all. But for the bulk of the population, pressure-treated lumber appears to be a reasonably safe choice for garden structures.
Pressure-treated lumber is saturated with a fungicide made from the salts of chromium, copper, and arsenic (CCA). These three chemical components, while potentially toxic to humans, occur naturally in some soils. The fungicide is applied to the wood under high pressure so that there is little movement of the fungicide out of the wood. However, some leaching is possible. Fortunately, the chemicals that do leach out of the wood become bound to soil particles in all but very acidic soils (pH 4.0 or lower). So even when leaching does occur, the chemicals are not likely to be taken up by a plant’s root system in quantities sufficient to harm plants or people.
Further Reading
Does Pressure-Treated Wood Belong in Your Garden?
Are Pressure Treated Woods Safe in Garden Beds?
Coating Pressure-Treated Wood to Make it Safer
Working with treated lumber is not risk free. The Environmental Protection Agency and the manufacturers of treated lumber advise that treated wood should be used only on outdoor structures, that a dust mask should be worn when cutting it, that scraps should not be burned, and that sawdust and chips should not be added to compost.
Although the risks of using treated lumber to build a raised bed are low, there are plenty of other materials available for building containers and raised beds. Rot-resistant woods such as redwood and cedar make excellent raised beds, but are relatively expensive. Synthetic lumber made from recycled plastic is also a good choice and is available in most places where lumber is sold.
