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The Myth of Allelopathic Wood Chips/Wood chips made from cedars will kill plants

stalk of fennel


Joined: Jul 12, 2010
Posts: 123
http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Allelopathic%20wood%20chips.pdf
Emerson White


Joined: May 02, 2010
Posts: 1206
Location: Alaska
Yay for thinking critically!
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14159
Location: missoula, montana (zone 4)
    ∞
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.


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Burra Maluca
Mother Tree

Joined: Apr 03, 2010
Posts: 3936
Location: Portugal Zone 9 Mediterranean Climate
    
130
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. 


What is a Mother Tree ?
stalk of fennel


Joined: Jul 12, 2010
Posts: 123
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
Burra Maluca
Mother Tree

Joined: Apr 03, 2010
Posts: 3936
Location: Portugal Zone 9 Mediterranean Climate
    
130
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. 
Jocelyn Campbell
steward

Joined: Nov 09, 2008
Posts: 2217
Location: Missoula, MT
    
  37
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?


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stalk of fennel


Joined: Jul 12, 2010
Posts: 123
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?
Tyler Ludens
pollinator

Joined: Jun 25, 2010
Posts: 5318
Location: Central Texas USA Latitude 30 Zone 8
    
  20
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.


Idle dreamer

Jocelyn Campbell
steward

Joined: Nov 09, 2008
Posts: 2217
Location: Missoula, MT
    
  37
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.... 
Matu Collins
steward

Joined: Feb 24, 2011
Posts: 1131
Location: Southern New England, seaside, avg yearly rainfall 41.91 in, zone 6b
    
  37
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...
Tyler Ludens
pollinator

Joined: Jun 25, 2010
Posts: 5318
Location: Central Texas USA Latitude 30 Zone 8
    
  20
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.


paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14159
Location: missoula, montana (zone 4)
    ∞
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.

Tyler Ludens
pollinator

Joined: Jun 25, 2010
Posts: 5318
Location: Central Texas USA Latitude 30 Zone 8
    
  20
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.

Matu Collins
steward

Joined: Feb 24, 2011
Posts: 1131
Location: Southern New England, seaside, avg yearly rainfall 41.91 in, zone 6b
    
  37
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.
greg patrick


Joined: Mar 17, 2012
Posts: 167
Location: SoCal, USDA Zone 10b
    
    1
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.


'Science is the father of knowledge, but opinion breeds ignorance.' - Hippocrates
Matu Collins
steward

Joined: Feb 24, 2011
Posts: 1131
Location: Southern New England, seaside, avg yearly rainfall 41.91 in, zone 6b
    
  37
Around here the best place for morels is under old apple trees.
Matt Baker


Joined: Dec 19, 2011
Posts: 38
I'm reading John Jeavons 'How to grow more vegetables'. It says Redwood compost impairs seed germination (2008 version page 64).


Kelowna, BC
Zone 5
Shawn Harper


Joined: Mar 01, 2012
Posts: 210
Location: Portlandia, Oregon
In my studies of the redwood ecosystem, few things tolerate them, ferns being one of them.


See the animal in his cage that you built, are you sure what side you're on?
 
 
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