The Myth of Allelopathic Wood Chips (that wood chips made from cedars will kill plants)

I have always avoided cedar and redwood in my hugels and bed mulch, but a friend recently reported good results with redwood in their hugels. I would bet the heartwood would be very slow to break down and give up its nutrients, but would be a good sponge that will last twice the time it took to grow. I have long given up any hesitation to use pine, spruce and fir, it seems to be great for many plants in a hugel, from acid loving fungiphiles to alkaline bacterial brassicas. I am doing an experimental Johnson Su compost setup with predominately fir and spruce as the carbon sources as well. I might try redwood next, and the more I learn the more I think it would be very diverse and beneficial given time, as much of the first wave of the green rush here was done on composted evergreen forest products, which means a lot of redwood. The main thing those tannins need to break down is time, and in return they lose less N and C to off-gassing (Noss, 1998).

Terrell Deppe wrote:I’m researching Huglekultur for use in Texas Hill Country,

Terrell, I hope you will report back to the forum as to how your hugelkulture turns out.

Dear hubby says they will not work in the Hill Country of Texas and I would love to say "This person did and it worked!"

No type of wood chips are a problem if they are aged and allowed to release the antimicrobial compounds contained in the wood.  Using your nose is a good way to tell if they are too fresh.  Depending on conditions, Aging means spreading them no more than 18 inches thick.  It will take much longer if they are in piles.  If it smells nice, then it should be aged more.  If it smells like nothing then it should be good.

Many species of wood chips will harm soil microorganisms until they are aged, as they receive rain or watering, some of the compounds move into the soil where they can harm organisms.  My experience as a Soil Food Web Lab tech has shown me (via the microscope) time and again that if I use fresh wood chips (of most types) to make compost, they will kill the microorganisms and the pile will not heat up, even when inoculating the pile with the entire soil food web and having plenty of food for the microbes, the wood chips can neutralize all that biology in the presence of their favorite foods.  That being said, the damage is likely to be less if chips are placed on top of the soil or in pathways rather than mixed in.  

If you harm soil biology, you harm trophic levels in the soil food web, and subsequently you are harming nutrient cycling for your plants.  So it is correct to say that wood chips don't kill plants directly, but they can certainly harm biology to varying degrees and affect plants accordingly.