Master Gardeners: Mulching from pallets and waste lumber

<div>Black pallet mulch used around a birch tree.  |  Julie Moore</div>
Black pallet mulch used around a birch tree.  |  Julie Moore

Organic mulches, those derived from plant material, provide many benefits to the plants in your yard. Mulch helps regulate soil temperature, reduces moisture loss in all seasons and inhibits weed growth. Beneficial soil microorganisms feed on the mulch and eventually break it down into organic matter. This is prized by gardeners because a soil rich in organic matter provides essential nutrients for plant growth, improves the ability of the soil to absorb water and improves soil structure.

Over the last ten years, mulches in stand-out colors have appeared in garden centers and for sale at the corner gas stations. In the mid-west, dark brown, red and black varieties are available for sale by the bag. Are these different from the composted hardwood bark mulch that can be purchased by the yard and delivered to your home? Richard Hentschel, University of Illinois Extension Educator in Horticulture explains, “This mulch is created by shredding recycled pallets, crates and waste lumber and is often referred to as pallet mulch. Every pallet and wooden crate shipped into our country is fumigated to protect our country from non-native insects, such as Emerald Ash Borer. The unknown is what is being used and it’s persistence on the lumber.”

A concern of what we are exposing ourselves to when using these mulches exists because there aren’t guarantees available regarding what the wood was treated with or exposed to while in transit. The wood is quite porous and any spills of just about anything could easily be absorbed.

“Pallet mulch is pretty much all carbon based. It has a very high carbon to nitrogen ration, which means it can temporarily deplete the soil of nitrogen that’s intended for plant growth as it tries to decompose,” notes Hentschel.  “It is artificially colored and seems to fade badly over time.”

“However, all these concerns are eliminated when you use composted hardwood bark mulch for your home landscape. There is a carbon to nitrogen ratio but it is much lower than pallet mulch, and there aren’t questions of safety.”

Somewhere along the way mulch became a landscape design element and it was never meant to be so prominent. “Think of mulching as way to feed the soil system that then feeds your plants, while it protects them,” recommends Hentschel.

Email your home garden and lawn questions to uiemg-dupage@illinois.edu or phone the Master Gardener Helpline at 630/955-1123. Visit our website at web.extension.illinois.edu/dkk

Julie Moore has been a Master Gardener volunteer with the University of Illinois Extension in DuPage County for 10 years and has a degree in Ornamental Horticulture from the University of Illinois.

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