What Lumber is Safe to Use in the Garden?

UNTREATED LUMBER
For wooden raised beds, untreated lumber is the safest to use. You can expect a raised bed made with untreated two-inch thick oak framing boards to last about 3 - 4 years. The lifespan of a raised bed made from untreated wood depends on the species of wood, the wood density, climate conditions and the location of the bed in relation to drainage, sunlight and the elements. Dry wood naturally has a longer life than moist wood. Since the soil in a raised bed must be kept moist for the plants to grow, the wood typically begins to decay as soon as the bed is planted.

Cedar and redwood have natural insect repellent properties, making them a good choice for garden structures. Paint or stain the wood to seal out water to prolong its life, or allow it to weather naturally. You can expect a raised bed made from these woods to last for about 7 years in a moderate climate. The above-ground parts of a fence, arbor or trellis could last 10 years or more. However, posts and areas that come in contact with the soil will need replacing earlier.

PRESSURE-TREATED LUMBER
The original Wolmanized pressure treatment for wood was developed in the 1920s for industrial uses such as shipbuilding, docks, piers and other marine applications, and for telephone poles, door and window frames, and other instances where the wood was exposed to the elements. The Wolmanizing process used chromated copper arsenate, or CCA, a poisonous compound that the FDA prohibited in 2003. CCA was followed by non-arsenic amine copper quat (ACQ) and copper azone (CA), chemicals that have also come under fire for metal toxicity.

"GREEN" LUMBER
A new environmentally-friendly pressure treated lumber process uses disodium octaborate tetrahydrate, or DOT borates, to replace the toxic chemicals. DOT borates are effective against subterranean termites, dampwood termites, drywood termites, powder post beetles, carpenter ants, other wood-destroying insects and decay fungi. You can purchase boric acid at hardware stores to spray on wood structures as a termite and insect treatment.

ES+Wood is an environmentally-friendly "green" lumber that uses DOT borates in the pressure treatment process to make the lumber insect- and fungi-proof. The lumber is then pressurized a second time with EnviroSafePlus®, a proprietary polymer sealing solution that is colorless and water repellent. ES+Wood does not contain metals, so it is non-corrosive to metal fasteners. ES+Wood is non-volatile and does not release toxins into the air. Use it for framing, flooring, joists, roofing, furring strips...any interior or exterior use. You can stain it or paint it just as you would untreated wood. It is the safe, long-lasting alternative for building wood decks, fences and play equipment. ES+Wood has a 40 year transferrable limited warranty.

WARNINGS
Although the EnviroSafePlus® solution seals the treated wood, some of the borates in ES+Wood do leach into the soil surrounding the point of contact. And although DOT borates are naturally occurring boron salts, high concentrations kill vegetation and affect plant growth. Borates kill fish and aquatic life. DOT treated lumber should not be used near a pond or waterway or where leaching could enter a pond or waterway. Garden structures such as an arbor or trellis should be painted or stained regularly to provide an outer seal over the treated wood to help keep excessive borates out of the soil.

BOTTOM LINE FOR GARDEN USE
For garden structures, DOT treated lumber is long-lasting. It contains no carcinogenic or mutagenic chemicals. Because the borates can leach out of the wood and affect plant growth, DOT lumber is not the best choice for framing raised beds or for building planter boxes. Never use DOT lumber around a garden pond or waterway, or upstream, where runoff could drain into a pond or waterway.

More Information:

http://www.eswoodtreatment.com/
http://www.eswoodtreatment.com/pdf/esptreatingprocess.pdf