6 Myths About Wood Chip Mulch

ChipChipAfter you’ve chipped up a big pile of brush or cleaned up those fallen limbs and branches after a storm, your first thought is probably “Great!  This project is done and it’s time for a cold beer.”  Your second thought should be, “Now what am I going to do with all these nice wood chips?”  Because you don’t want to waste that stuff!  There are all kinds of ways to use wood chips around your property, but the number one thing that most people (I’m guessing) use their wood chips for is mulching gardens and flower beds.

Wood chip mulch is great for keeping the weeds down, retaining moisture, keeping soil from eroding away, and keeping your flower beds looking nice and uniform.  There are a lot of worries floating around out there, though, about bad things that wood chip mulch can do to your gardens.  According to the folks at the Puyallup Research and Extension Center at Washington State University, most of them are bunk, and wood chip mulch does much more good than harm.

Myth #1: Wood chip mulches will acidify soils.

Truth:  It makes sense that gardeners would worry about their mulches changing the pH of the soil underneath, especially if  you’ve gone to the trouble of testing the soil and making sure it has the ideal acidity.  There is no evidence, however, that wood chips mulches that sit on top of soil will change the soil’s acidity.  Some studies showed that the soil was a tiny bit more acidic right at the top where the mulch would start to decompose, but never deep enough to affect plants’ root systems.

Edge of Perennial Flower Garden with Wood Chip Mulch

Myth #2: Wood chip mulches can leach chemicals into the ground and hurt plants.

Truth:  Many plant materials do contain chemicals called allelopathic chemicals that can prevent seeds from germinating or kill small seedlings.  Most, however, have no affect on established plants, and few to no woody materials (what your mulch is made out of) contain them.  Bottom line: don’t worry about mulching established plants, and if you mulch seedlings, do a bit of research into the type of wood chips you’re using to make sure they do not contain allelopathic chemicals.

Myth #3: Mulch made from diseased trees can infect healthy trees.

Truth:  There is no evidence that mulching around a tree with wood chips made from a diseased tree will transmit disease to the healthy tree.  Do not, however, backfill the tree’s hole with wood chips, this can transmit disease.  On top of the soil, though, you’re in the clear.

Myth #4: Wood chips can be a fire hazard.

Truth:  Coarse, organic mulches such as wood chip mulches are actually the least flammable of all landscaping mulches.  Finer mulches are slightly more flammable, and rubber mulches are the most hazardous.  Learn more about what you can do to protect your property from brush fires here.

Myth #5: Wood chip mulch will cause a nitrogen deficiency in your plants.

Truth:  Studies show that wood chip mulch actually increases a broad range of nutrients in soil and plants — including nitrogen.

Myth #6: Wood chip mulch will attract termites, carpenter ants, and other pests.

Truth:  Most wood chip mulches are actually really unattractive to pests and act as a repellant.  Cedar, for example, produces thujone, which repels everything from moths and termites to ants and cockroaches.

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  • Shar

    #6 is NOT A MYTH!!!!! Ask any termite SPECIALIST!!!! I live in an area with termites and actually lost my home to termites with no visible signs until my house was ready to collapse and termite damage is NOT covered by any insurance policy. I had a couple bags of wood mulch laying in my yard and when I went to move it = each bag was full of termites! Termite specialists will tell you not to put wood piles or wood mulch anywhere around your house. Termites will also eat cedar – they destroyed a cedar deck! They will even eat creosote railroad ties.

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  • Park

    I live in AZ & have a lot of mesquite trees. They drop beans & leaf needles, and these seem to be detrimental to a lot of plants. I’ve had a lot of container plants die or wither after being under mesquite trees …

    Park A.

    • park

      Because of this I remove most plants from around them and would never use the wood chips. The soil here is very alkaline, I usually add sulfur but it’s effect is minimal as there is lots of calieche everywhere…


    • DRPowerGrace

      There doesn’t seem to be any evidence that using mesquite wood chip mulch to mulch trees and flowers would be harmful. But if you find that it doesn’t work for you, go ahead and avoid it.