Are Landscaping Timbers Safe for Garden Use?

Landscaping timbers available in many home and garden centres nowadays are made from the center wood of trees which have been refined for plywood and are seldom dangerous to use in your garden. However, before 2004, landscaping timbers were treated with a solution which contained arsenic, which may not be safe for use in your garden, particularly if you’re growing edible plants or have pets that may chew the wood.

The Concern

Landscape timbers used as garden edges or as part of increased beds are in continuous contact with the ground. Prior to 2004, landscape timbers were treated with chromated copper arsenate (CCA) to prolong the life span of their timbers, but insecticides, among the substances used to create this preservative is extremely poisonous to people and other non-target organisms. While the number of chemicals leaching into the soil varies based on environmental and soil conditions, the health risk associated with long-term exposure to toxic substances through edible plants is actual. However, according to the Environmental Protection Agency, as of January 2004, producers voluntarily stopped using CCA for many goods meant for use in residential applications.

Identifying CCA-Treated Wood

CCA pressure-treated wood is easily recognized by its greenish tint, particularly on the cut ends, and by grooves or slits which line with the wood, which are approximately the size of a staple. However, older timbers fade and may no longer retain the green shade, and a few timbers, such as Wolmanized forests are treated with CCA, but resemble regular timber, with no slits or coloring. If you are uncertain of the age or supply of a particular timber, avoid using it in your own garden.

Safe Utilization of CCA-Treated Timbers

CCA-treated landscaping timbers are still considered safe to be used in a variety of outdoor structures, including decks, fences and gazebos, but should never be used in vegetable gardens, or where the wood may be in contact with food. The EPA advises against using CCA-treated lumber as a mulch or compost stuff, so it is ideal to avoid using it from the garden completely. If using timber which may have been treated with CCA close a vegetable garden, then line the soil prior to installing the timbers with plastic or another watertight, non-toxic substance to avoid direct contact between the wood and the soil.

Garden-Safe Landscaping Timbers

There are numerous kinds of landscaping timbers which are perfectly safe to use in your garden, whether you are growing ornamentals or edible plants. Untreated woods which are naturally pest and weather resistant such as cedar, juniper and redwood are perfect for garden use, or you may investigate non-wood landscaping timbers, which are generally made of plastics, metals and wood composites that contain recycled wood fibers. Most of the landscaping timbers currently sold to be used in the home landscape are handled using less-toxic solutions that contain copper and boron, such as ACQ, which stands for alkaline copper quaternary.

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