Released: January 15, 2003

Treated Lumber Need Not be Replaced in the Garden

MANHATTAN, Kan. – Lumber has taken its place as a valuable landscaping component, but concerns have surfaced among gardeners recently about chemicals used to treat the wood.

Lumber commonly used in gardening is often treated with chromated copper arsenate (CCA), said Chuck Marr, Kansas State University Research and Extension Horticulture state leader. CCA contains arsenic, a highly toxic substance, which has prompted the concern.

Some lumber companies have voluntarily moved to replace CCA lumber with two newer compounds that do not contain arsenic.

"Some people question if they should remove CCA treated timbers used in garden bed construction because there may be a danger of arsenic getting into the things we grow," Marr said. "The answer in a word is ‘no.’"

The copper and arsenic combination provides protection against wood rotting fungi and bacteria. Bound by chromium, Marr said the insoluble, stable material does not leach or move into soil.

Roots will not penetrate the lumber for the same reason fungi and bacteria won’t attack it, he said. Therefore, arsenic cannot get into the food supply from roots growing near CCA-treated materials.

"There is a much greater concern from direct contact from CCA materials by wood used for patio decks, swimming pool decks, playground equipment and related construction where people come in direct contact with the wood," he said. "The chance of human contact in these situations is much worse than for gardening."

The Environmental Protection Agency, as well as plant growing experts, have conducted numerous studies regarding plant uptake. The current recommendation is to not consider replacing any treated gardening structures unless building new ones, Marr said.

The two new compounds replacing CCA materials rely on non-arsenic materials, called ammoniacal copper quat (ACQ) and copper boron azole (CBA). Both rely on copper and other compounds to prevent attack by fungi and bacteria, he said.

CCA may still be used for some industrial applications such as utility poles or railroad ties where limited contact with people occurs.

"The lumber will not harm you and treated lumber will last for many years in the garden environment," Marr said. "If you have any concern when constructing new beds, add a sheet of plastic to the face of the lumber coming in contact with the soil."

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Lucas Shivers, Communications Assistant
lshivers@oznet.ksu.edu
K-State Research& Extension News