Is Composite Lumber Safe for Raised Garden Beds?

Composite Lumber

• Composite lumber is made from a combination of recycled plastic and wood products, including trash bags, milk jugs, fiberglass, peanut hulls and wood waste fibers. The composition and ratio of wood to plastic varies depending on the manufacturer. Composite lumber is available in hollow grade for low-load structures and in solid grades for medium- and high-load structures. Composite lumber generally has the look of wood but can be painted as well.

Advantages

• The lumber used to build the frame for a raised garden bed comes in contact with insects in the ground, the soil and water in the garden and sometimes with harsh weather. However, composite lumber resists rotting, chipping, warping and insect damage. Composite products can last in the garden for 10 to 50 years with little or no maintenance. You can use regular woodworking tools to build your frame with composite lumber without the fear of releasing harmful vapors as when working with some wood or pressure treated lumber. Finally, composite lumber does not contain any harmful chemicals that might leach into the soil, and it has a low-absorption rate, making composite lumber a good choice for ground contact projects like a raised garden bed.

Disadvantages

• The initial cost of building with composite lumber is higher than with other types of lumber. However, composite products require less maintenance over time, which may offset the high cost. Also, because it is a blend of biological and manufactured waste, disposing of composite lumber is difficult -- because it resists decay, it will not decompose readily and you cannot recycle it. Finally, because of its construction, composite lumber is heavier than wood and requires screws and bolts made especially for composite lumber.

Other Options

• Although composite lumber might be priced outside of your garden budget, and many types of wood lumber carry concerns of chemicals leaching into the soil, other building products are available for creating your raised garden bed. Stones, concrete blocks and bricks also create attractive retaining walls, especially if they’ve been recycled from another building project.