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

Yay for thinking critically!

That PDF seemed to say nothing.  I was waiting for the part that said "so we set up 40 difference species and for each species we had twelve samples.  Two samples were a control, two were mulched with compost, two were mulched with cedar, two were mulched with hay, two were mulched with douglas fir chips, two were mulched with straw.  The results were ...."

Instead we got "What those people over there said ....  yeah, that's a myth.  And me ... what I say .... well, I speak the truth."

Lame.

I tried following the link given in the paper.  It took me to a site where I found the relevant section, clicked on the link, and it took me straight back to the original paper.   

Of course, she might be right in what she's saying, but she's not exactly offering much evidence for it. 

Well I started digging around.  Gotta get that knowledge.  Here you go Paul   I think the good Doctor may have been getting her information from the 7th link down.

Well she is saying that there isn't any evidence out there.  I wouldn't normally link to an ehow article like the one below but it sent me off in the right direction with a reference to a Drake University study.
http://www.ehow.com/about_6399802_do-trees-strawberries-grow-together_.html

Study talked about in the link above.  Drake University Study
http://escholarshare.drake.edu/bitstream/handle/2092/956/Poster%2020.pdf?sequence=1

Interesting article about how Allelopathy is tested for in the lab.  Makes mention of a few plants but not cedar.
http://csip.cornell.edu/Projects/CEIRP/AR/Allelopathy.htm

This pdf from the UF says that 'Preliminary reports indicate that wood extracts inhibit lettuce seed as
much as or more than black walnut extracts'  They give no indication on what kind of study was done or how they come to that conclusion.
http://edis.ifas.ufl.edu/pdffiles/HS/HS18600.pdf

I wish I could get the whole book but this small section seems to indicate that White Cedar has effects on grasses germinating.  I actually read somewhere else that cedar effects monocots but not dicots.
http://books.google.com/books?id=5-3AEm2erJIC&pg=PA348&lpg=PA348&dq=cedar+allelopathy+study&source=bl&ots=mLxeTJ2nd_&sig=IVsh9idgU-F1LOnksb6VDw2O_L0&hl=en&ei=dtZjTcn0BsO78gaQ8cTpCw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCsQ6AEwAw#v=onepage&q=cedar&f=false

Here's another article about woodchip mulch coming from the same source.  She speaks of a study done with 15 different types of mulch that wood chips where one of the best.  She doesn't mention how the study was conducted though.
http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/magazine%20pdfs/Woodchips.pdf

Maybe the most intersting study done, yet they don't really study cedar.  This is the first scientific study I've seen where they study the soil pH under different mulches.  After 1 year pine needles had shifted the soil pH down (more acidic) but after 15 months there was no difference in pH under the various types of mulch.  It also says:
"The presence of hydroxylated aromatic compounds in all 6 fresh mulches and the demonstrated inhibition of germination
by fresh mulch extracts suggests that, at least initially, all the mulches have allelopathic properties to
some degree. With mulches, allelopathic properties could have 2 possible impacts: 1) a mulch might inhibit
germination of weed seeds, or 2) a mulch might inhibit growth of landscape plants. After 1 year in the
field, there was no difference in the number of weeds growing in any of the mulches. The study comparing
15 organic mulches showed less weed growth with mulches compared to bare soil but no difference between
all the mulches tested"
Another thing I really like reading here was that mulch generated by utility services had the highest nutrient value of all the mulches but that it also broke down the fastest.  I suppose this makes complete sense because of the diversity (where have we heard that word before) of material.
http://www.treelink.org/joa/1999/march/06_COMPARISON_OF_LANDSCAPE_MULCHES_duryea.pdf

This article said that they tested five prairie grasses and one of them was effected by Red Cedar.  Reading about how they went about the study makes it seem like not a very good way of going about it.
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1015&context=napcproceedings

One last study.  Comparing magnolia and cedar (juniper actually).  Seem to have about the same effect on seed germination.
http://www.fngla.org/education-and-research/research/reports/161/report1.pdf


To me it looks like all wood based mulches have anti germinating effects on seeds, especially monocots (grasses).  It doesn't seem to me that cedar is any more of an inhibitor then the other wood based mulches.  Enjoy the read

Well done, Stalk of Fennel!  That's more like the kind of info we need!

I haven't gone through the whole lot of links yet (I will, I will) but I get the impression that white cedar might be a jolly good sort of mulch to put in your veggie garden around your plants to stop the monocot grasses growing up as weeds around the dicot veggies. 

Interesting. Though the myth she's debunking is not one I've heard of. I've heard tell of conifer wood chips making it harder for plants to thrive, not all-out killing them. It makes sense that it's unlikely that conifer wood chips would kill plants.

The article mentions that cedar inhibits bacteria and fungi. That's a positive when you want your wood to last in the outdoors, but not so much in the garden. Thoughts?

Jocelyn Campbell wrote:
Interesting. Though the myth he's debunking is not one I've heard of. I've heard tell of conifer wood chips making it harder for plants to thrive, not all-out killing them. It makes sense that it's unlikely that conifer wood chips would kill plants.

The article mentions that cedar inhibits bacteria and fungi. That's a positive when you want your wood to last in the outdoors, but not so much in the garden. Thoughts?

interestingly enough morel mushroom season is about to start here in central texas.  apparently they are only found in cedar/juniper groves on sloped limestone ground.  weird huh?

Cedar only inhibits bacteria and fungi to a point.  In a moist, living environment such as the soil, there's so many bacteria and fungi they will eventually rot the chips especially since they have such an enormous surface area.  Add in some manure and there's no problem, in my opinion.  Rot will only be inhibited for a brief period.

Oh man, I replied without refreshing my browser from last night, so I was waaayyy behind on this topic! And here I'm replying and Ludi has already posted. You guys are too quick!

Wish I could read more of Fennel's links for some real info, because I agree that article raised more questions than it answered, but I'm going back to work.... 

So I have a cedar tree that is almost dead and is in an inopportune place by my driveway. I am thinking of having the friendly tree service man come and cut it down and chip it for mulch. Would it be ok to use it in the garden paths? How about under yew bushes where the children like to play but the asian bittersweet and the multiflora rosa would like to take over? I don't want to harm the plants and bushes, I know cedar oil is strong...

Matu, personally I don't think there will be any problem. I'm using cedar (juniper) mulch in my vegetable garden and not seeing any problems so far. Some areas have been mulched for months, others freshly mulched, everything seems to be doing great. This is mulching around established plants, I don't think cedar mulch should be put close to baby plants. If you're very worried, leave the chip pile out in the weather for a few months for the oil to break down.

the ehow article: is no longer there. perhaps they found it lame and took it down?

the drake study: when you read it, they boiled cedar foliage. I wanna toss the whole study because the stuff we are concerned about is not boiled, nor is it the foliage. We're talking about dominantly the bark and wood.

At 0 for 2 I don't much feel like picking through the rest.

I think the concern about allelopathy is still valid. I know that I will minimize my use of cedars. Further, I will prefer the use of cottonwood and poplar over any conifer. Further still, for a lot of wood matter, I would have a slight concern about any persistent herbicides the tree might have taken up.

I forgot to mention the chips I'm using are not 100% cedar/juniper, they are about 50% with the rest being oak and other species, so it could be these other woods are offsetting the toxins in the cedar. Also these are chipped whole branches including leaves, not just wood.

I wouldn't use cedar on purpose if I was choosing, but I use what I have here in preference to inputs and what I have is a cedar tree in an inopportune place which is almost dead. It does seem to me that if cedar oil is used for pesticide, it will upset the balance of life in the soil. I think I will avoid using it in my garden and just put it under the bushes where the children can play. Thing is, I want some chips to delineate the garden paths for the people who come to help me out on the farm. To me it is obvious which plants to step around and how to follow the paths, but I am finding that it is not so obvious to the feet of those who don't see with my eyes.

I am thinking that if I had a sawmill I could make cedar boards for a storage closet, but I have no sawmill.

I have designs on all the cedar trees on my property, as cedar apple rust is an issue here, but even if I took them all down there is cedar woods nearby, so my vengeful feelings would be for naught. Those rust galls are pretty bizarre. We end up using most of the apples for cider.

stalk of fennel wrote: interestingly enough morel mushroom season is about to start here in central texas.  apparently they are only found in cedar/juniper groves on sloped limestone ground.  weird huh?

We find morels here in open pine forests, at 6000', east facing aspects. Mulch is mulch.

Around here the best place for morels is under old apple trees.

I'm reading John Jeavons 'How to grow more vegetables'. It says Redwood compost impairs seed germination (2008 version page 64).

In my studies of the redwood ecosystem, few things tolerate them, ferns being one of them.

In: The Holistic Orchard: Tree Fruits and Berries the Biological Way. Michael Phillips references cedar chips disrupting the preferred mycelium relationship for fruit trees. One may deduce the allelopathy of Cedar would do the same thing in soil. Any thoughts on this?

A neighbor just had a bunch of cedar chipped and I convinced the kind tree service man to dump the chips at my place.

I'm going to use a blend of the cedar and some aged spruce chips to mulch the blueberries. I hope there's enough, I like my blueberry mulch thick

Earlier today I was feeling good about this and now I'm having doubts. I need to mulch now but the chips are fresh. Maybe I will mulch some of the bushes with the cedar blend and some with only the spruce. Just to see for sure if allelopathic wood chips is a myth.

Feel free to talk me out of my doubts.

Interesting addition: Geoff Lawton said in interview that some of the most diverse soil life him and associates tested came from beds that DID contain some allelopathic woods like cedar.

The theory was that the allelopathy made a tougher climate for some and an easier climate for other.

I'm not sure I'd want to add a ton of cedar, but some seems to be fine, if not helpful.

Matu Collins wrote:Earlier today I was feeling good about this and now I'm having doubts. I need to mulch now but the chips are fresh. Maybe I will mulch some of the bushes with the cedar blend and some with only the spruce. Just to see for sure if allelopathic wood chips is a myth.

Feel free to talk me out of my doubts.

The cedar chips will increase acidity but they would work best if used in a hugelkultur way (buried in a mound with the blueberries planted on the mound) If you want to age the cedar a bit, get a large washtub and soak the cedar chips, set the washtub on some blocks and heat the water till it is near boiling, this will help extract some of the oils that could be a problem. the longer you keep it heated, the more that will be extracted. Once you are happy with the amount extracted, simply dip out the chips, spread them on papers to cool and spread around your blueberries as thick as you like.

I just dug a big terrace so I have a lot of exposed soil to cover, and I’ve been trying to think of the best way and the best source to cover it. While I was working on my ERC (J. virginiana)-post wood shed, my new neighbor showed up and offered more posts and/or wood chips for free and he’ll put them wherever I want them. So now I have a potentially great source of great stuff to use, but would I regret it because of allelopathic effects??? Of course I come to permies.com to try to find out.

Somebody (the name is blocked- is it, was it, Stalk of Fennel??) said, “Reading about how they went about the study makes it seem like not a very good way of going about it,”
about this link:
http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1015&context=napcproceedings

I don’t know what you found wrong with the study. I thought it was great, though maybe a longer-term study would’ve been even more informative. I guess I particularly liked it because it really pertains to me, as it is closer geographically, and I have all those species on my land too. (Thanks for all the links by the way!)

My complaint is with their conclusions; they seemed to WANT to find evidence to dislike Juniperus virginiana. Their interpretation of their results (only one was affected so be VERY careful) is the opposite of my interpretation (only one was affected, so no big deal). And in a contrived experiment, who knows which other important variables they may have neglected, inadvertently manipulated, etc.?

By the way, in a completely natural and accidental observational “study,” I have a thriving finger coreopsis (Coreopsis palmata) within a few yards of a group of 4-6’ tall J.v. and several leadplant there too. Although they’re all near the cedars but not really in the cedar-affected soil yet. If I decide to leave those cedars there and just prune the lower branches, I bet all the existing plants (a lot of B. inermis too) will be totally fine, even as more soil gradually comes under the cedars’ effect. It will be interesting to see whether the Amorpha and Coreopsis might even germinate some more. I suspect that shading and competition for moisture are the main issues. This is on a south-facing slope, so with a little pruning lack of sun won’t be a problem but moisture competition will be. I’ll try to remember to leave that particular area alone and report back in a few years. Hopefully this post will help me remember.

Very interesting addition from Matthew McCoul regarding Geoff Lawton. Even though I have no idea whether he was talking about Cedrus, Thuja, Juniperus, or some wacky upside-down Australian “cedar,” that's what has made me decide to go ahead and give the J.v. chips a try. I’ll have to remember to report back on how that goes too. (I guess veggie growers won’t much care what my results are because I won’t be trying to grow a garden or anything, just need to hold the soil in place. We’ll see if I can get some stinging nettles, purslane, lambsquarters and stuff like that to grow there though.)

I don’t doubt that J.v. can inhibit germination, and it definitely DOES become thick stands of nothing but J.v. (there are many examples of that around here). I hope that thinning out those thick stands, building with the straightest logs, and chipping the rest is something that helps me build my soil cheaply and by making others’ problems my solutions.

Oooooh, speaking of thinning and/or removal, this is interesting:

http://www.fws.gov/southwest/es/documents/R2ES/LitCited/LPC_2012/Pierce_and_Reich_2010.pdf

(My guess about soil moisture seems to be incorrect.)

I found the stuff about potassium under the trees particularly interesting. I just got the results back from four soil tests. The two samples from down in the alfalfa fields (far from any J.v. are very low in K. Another soil sample was taken from the brome/J.v. area and the level of K there was right where Gary Zimmer says it should be (btw, the J.v. scattered throughout the brome here are 4-15’ tall and dbh of only about 1-5”). The fourth soil sample was taken in a low, moist area that’s near some older, larger J.v. and the K level there is way too high. (Though I should mention there are other confounding factors with the fourth sample- the nearest J.v.’s are about 10 yards away, this is the one sample not taken from a S-facing slope but an E-facing slope, and it was taken from a under a thick patch of burdock.)

Just like with any “opportunistic species,” they seem to be there for a very good reason. After previous landowners have mined the soil by removing hay year after year, and (I’m guessing) mindlessly added way too much lime instead of, say, K-Mag which would have improved things rather than liming the soil which resulted in very high pH and a bit too much calcium. The J.v. are here to accumulate needed K in the soil. And at least according to this study, they DON’T raise the pH which is good news because it's already too high here. I’m hoping the common belief about wood chips lowering pH is true. If so, then the path forward for me has become clear!

This is an excellent discussion regarding cedar and its allelopathic properties. I've been hard-pressed to find anyone as well researched as those on the Permies forum.

I am about to clear 15-20 smaller cedars in the Hill Country north of San Antonio to create a clearing for a future retirement home. Mountain cedar is the common name for the Ashe juniper trees that grow thick around here. They aren't large with thick trunks that will provide a lot of mulch. Instead they are 10-20' in height and very bushy. I intend to cut them and let them dry out for a year or so to reduce the oils before putting them toward any purpose.

My question is this. Should I cut them at the trunks and keep the roots in the ground? Would they act as a good pre-installed huglekulture bed? I could wrap a chain around them and pull them out of the ground but it seems like more work. My initial plan was to leave the roots in, drill into them and introduce some mushroom spawn to them. Maybe pee on a couple others. Thoughts?

Sean Haseloff, I am not sure that introducing mycelium spawn into juniper roots would be productive. The Sacred Cedars (junipers) that I have on my land don't seem to support mushroom growth or decay at any worthwhile pace when left for mother nature to take care of. I have three that have been down and dead for at least 6 years and there is no indication of them even starting to rot. These are in an area that have several oaks and hickories that are down and full of termites and have several different species of mushrooms growing all over them which include; turkey tail, Jew's ear, and chicken of the woods.

I have experimented on one of the downed junipers and so far, the only treatment I've had success with is from lye derived form hard wood ash by the leaching method. I do not use "chemical" solutions since they are normally not adsorbed by nature as easily as those derived from nature.

Good point Bryant. I will now be pulling them out of the ground.

What would the use of multiple cedars be then? I can mulch them up but won't have any use for the mulch on raw land. I can spread it around and watch it NOT break down for years. I can put it in a pile off in the corner of the land, possibly for use in MANY years down the road on walkways, etc.

Anyone have any ideas other than harvest smaller fence posts out of them?

I should save this one for the dark of the moon close to Samiam, I Have a small clump of Box Elder, the Elder wood of song and story, and a 7 part Wizards phantasy .

It, like Tamarack is extremely hard to burn up ! And even though slow growing, is very hard to kill ! As proof of that I pen my observations !

Extremely hard to burn up 1) In Olden times, a piece of box elder might be cut as a combination walking staff / fire poker. A common Meme of that time Would

show in carefully carved woodcuts (prints) the bent old crone using that same now much shortened cane / poker to symbolize great age or passing of time !

While the Production of maple syrup now seems more and more to be taken over more and more by the big guys, with even local Fram families banding together to
work their sugar bushes together, It is not uncommon to find that a 6'-8' length of Elder-wood receiving a place of honor amongst several pokers for stirring up the
fire under a maple syrup hearth !

I too have seen remnants of these Elder-wood pokers now much reduced in size saved in a special corner, just saved out rather than added to the hearth fire because

it was the one Great Granther used for poking up the fire and " You might burn it up, but it won't make no heat anyway !''

Hard too destroy by cutting down ! I have cut down the individual clumps of trees at my multi generational home only to have then grow back like other Coppiced

trees with renewed vigor !

After cutting an elder wood treating a foundation wall, I took a slurry of Butternut husks and covered the cut top with this mess and sealed in the whole thing by wiring

in place a thick freezer bag over the whole thing !

Due to its location sheltered from UV rays the bag and contents serviced for about 5 years before failing apart ! During that time the Elder wood appeared dead with

zero sucker growth !

I now estimate the regrowth of that clump to be a vigorous 15 years old post Allopathic treatment, Certain friends charmed by this story have requested cuttings, both

for replant with mixed results and as walking sticks !

4 th Craft Big AL

We trialed digging in fresh Eucalyptus chips into a broccoli bed, found that up to 2" of chips didn't effect the plant growth at all.
However 5" of fresh dug in Euc chips did stunt the plants growth all season.

Have a video report here:  

The link from way back seven years ago in the original post has gone dead, but I was able to find a replacement in the WayBack Machine.  I agree with Paul and other commenters that it doesn't really establish what it claims, though, even though I myself am in the camp of believing that allelopathic concerns are frequently overblown, and I rarely (never) worry about them with regard to the usual suspects that grow in my own landscape.

Not a study but... I have a pile of cedar chips at my place and clovers and grass were growing right through it. Vegies could be different but I thought it was interesting to see.

Seems to me that what is often referred to as alleopathy is really just anti-fungal and anti-biotic oils in the wood. The chips aren't actually harming the plants but are inhibiting the beneficial microbial allies that plants use to thrive. I live in redwood country and the eastern border of my yard is defined by a row of redwoods, my minihugels end about 6 feet west of those redwoods and that end of them is definitely less productive and more prone to weed pressure than the rest of the bed. However part of that is certainly because those very eastern edges often don't get sun until well into the afternoon. Whatever alleopathy I personally believe I have observed has been an effect of living trees (maybe a root exudate?) and not an effect from the dead wood.

Next to my house is a big Western RedCedar stump. I tried planting MINT in the soil next to it. Multiple different plants either died or were stunted. I excavated a bunch of the soil to make a hugel. Not much is growing in that hugel other than buttercup. The veggies are stunted or not germinating.

Up at the top of my hill, is very cedary and hemlocky soil (lots of trees fell up there and the soil seems to be mostly decomposing cedar/hemlock). Even though it gets good sunlight, the grass really doesn't grow.

So, either because it's so fungal or so nitrogen-deficient, it doesn't seem to grow veggie plants or grass too terribly well.

BUT, it grows other things! Black cap raspberries, red huckleberries, salal, oregon grape, salmonberries, thimbleberries, trailing blackberry all grow fantastically in this environment. In fact, up at the top of my hill, red huckleberries are sprouting up everywhere in the soil (one usually only finds them on cedar logs).  Blueberries and strawberries also seem to be doing well, too. So, I just grow that stuff in that soil, instead! I like berries, so it's not really a problem for me .

I am travelling, but when I get home I will post a picture of grass growing in a cedar stump I cut this year! I throw out seed mix after the chux go through, and they were in the paddock maybe three months ago. I think it must be nitrogen depletion, because the birds love to perch on it and poop.

I'm thinking the allelopathy is probably inhibiting mycorrhyza if it exists. Since it has some intrinsic antifungal properties to prevent rot that makes sense.

Plant allopathy comes from living tissues and it can remain in soils for over a year after the plant is dead and removed.
If you cut a tree, the root system will not die, it will usually remain alive for at least a year after the top has been removed, if it is coppice type tree, it will live for as long as it can produce new shoots.

Heart wood does not contain any of the life fluids (sap) and so has nothing that could operate as an allopathic provider.

Generally plant allopathy effects only other plant species, not the soil organisms present, those allopathic plants need the soil food web to survive too.

Redhawk

I read fairly quickly through this whole thread, didn't see what I'm thinking of: using cedar and walnut chippings for my paths, to keep down the vegetation. Is this a good or bad idea? Did I miss it in this? I have both on the property and they are thick in the area.

I tried laying down cedar branches to smother weeds. I'd do layer after layer....it didn't do much to stop the grass, and nothing to stop the buttercup or bindweed. Maybe woodchips would work better, but just the Allelopathy of the cedar did nothing against the weeds. Allelopathy+smothering might be better than just smothering, but I think many weeds aren't stopped by the Allelopathy.

I’m researching Huglekultur for use in Texas Hill Country, and stumbled on this thread. While my input is not scientific, I can tell you that cedar chips have had no impact on germination for us, and about the researcher that educated us. We have almost all Ashe Juniper (“Mountain Cedar”) on our property, and we refuse to cut down our precious Live Oaks to make a Hugle. Any Hugle we do will be all Ashe Juniper, and I have no reservations about doing so.

We currently use juniper logs and wood chips for erosion control. It not only works for erosion control, but promotes natural grass development. I’ve even thrown grass seed on top, and it sprouted as expected.

Over time (a year or two), the chips disappear under a layer of new top soil and grasses, some of which is created by new growth, and some as a result of catching nutrients from runoff. Large patches of bare limestone have totally disappeared even when all we did is throw chips on a small portion of the downhill side of the rock.

I was surprised to see so much speculation andconfusion here about cedar and juniper, and relatively little real world experience so I decided to throw our experience out there. For what it’s worth, I learned about doing this from a PhD biologist at the Texas Biomedical Research Institute (formerly the Southwest Foundation for Biomedical Research) about 15 years ago. He told me about a volunteer study he did on his own with some ranchers in hill country, and how many have stopped burning the cedar. They are now relying on cedar eaters (commercial services) to grind the shrubs and trees. They get less erosion and better grazing for the cattle in a shorter period of time.

It has proven to be true for us as well.

Side note: University of Michigan and UConn have done long term studies (since 1992) on the impact of mulching oak and maple leaves. There was no effect on the soil PH the following season, and nitrogen was significantly elevated. The tannins (acids) leach out very quickly especially when mulched.

Hopefully this is educational. Time for me to get back to learning about Hugles and how to build a productive one in Texas Hill Country…