I mulch with cedar play chips. Wonderful! Best mulch I have ever used.

I do not amend planting holes. This is a disproven practice. When I want a layer of "better" dirt I lay down topsoil.

Compost is an excellent topdressing/mulch, especially for improving existing soil conditions and adding organic matter. And it typically reduces/eliminates the need for any supplemental fertilization. 2-3 inches is an optimum amount when used for this purpose. Since it continues to degrade and breakdown after application, there is minimal risk of applying too much over time or burying the plants -- in fact, the shrinkage is enough so that those who use compost as a topdressing routinely apply it annually or semi-annually. Feather it out to a thinner amount as you approach the crown of perennials.

Mixing in arborist wood chips will extend the lifespan of the mulch - it's a personal choice but I don't care for the texture or appearance of the chips in a mixed planting situation that features perennials or smaller plants. Too coarse. But the wood chips do offer better weed control.

btw, the Bailey's compost is the best I've encountered.

Compost and other fine mulches sprout weeds, may form a crust. And the water saving feature of mulching is partly due to the difference in texture between the soil and the mulch. But you do have to keep cedar play chips well back from small plants in particular, otherwise these are liable to end up buried in mulch. This is true of mulching generally, a space should be left around each plant so that the crown does not become buried. Some plants are more affected by this than others.

Most people I know avoid using cedar chips for any kind of mulch. It has something in it, (some say it's formaldehyde, but i don't know the actual chemistry) , that will kill strawberries and definitely impedes the growth of seasonal veggies. We use a lot of chips as mulch in our big gardens, as deep as 4 inches if we can get it, and we always try to make sure the chips are pine, alder, fir, maple, or madrone.

We do use the cedar as well, but save it exclusively for our chicken coop, where it definitely keeps down the flies.

There is no formaldehyde in cedar, either Thuja or Cedrus. Formaldehyde is a chemical compound that is a byproduct of combustion. While it does exist in nature, it requires some sort of oxidizing process to be released. Most formaldehyde is manmade. Moreover, neither species has been proven to have any significant allelopathic effects or release any chemicals that may impede the growth of other plants. In fact, Western red cedar mulch is one of the most long lasting, inexpensive and widely used wood mulches in this area.

I'd suspect your experiences with your plants may have been the result of the cedar mulch somehow becoming incorporated into the soil. This can tie up available nitrogen and that can limit or impede the growth of very young plants or seasonal crops.

Here is a link that might be useful: The myth of allelopathic wood chips

My own experience is that red cedar, as mulch, displays a definite tendency to impede flower and fruit production. What you insist is a "myth", is a common experience shared by many, many other knowledgeable gardeners and farmers where I live. I invite you to do your own test on 2 strawberry beds, one mulched with cedar, and the other with pine.

OK, maybe it's not formaldehyde, but i wasn't sure anyway, and thanks for verifying that. But whatever is in cedar that so obviously retards the chips from the usual breakdown process of just about every other local wood, is what we have always presumed to be the problem of using it as a mulch. Maybe you can answer, for all of us, why red cedar is so immune to the usual bug, bacterial, and fungal processes that cause every other kind of wood to break down within a season. And why flies avoid cedar so thoroughly in a chicken coop.

If i was really hard up, I might use cedar chips sparingly in a flower bed. But never on anything I was growing for food.

Did you bother to read the link? I am not the one "insisting" it is a myth.....it is a commonly held position and one that is backed by science. It is the lack of research and instead a reliance on unsupported and untested anecdotal reporting that promotes the persistence of these allelopathic contentions despite all evidence to contrary. The link also answers your questions as to why cedar is such a rot-resistant and durable wood, but by no means the most durable or rot-resistant (see attached link). And the same phenols and turpenes that resist decay also repel insects.

And it should be noted that most cedar mulch sold here is primarily bark that is a byproduct of the cedar lumber industry. The wood is a bit too valuable to be simply ground up for mulch unless it too is waste. And the bark is the portion of the tree that has the lowest concentration of thujaplicin and other phenols - they are centered in the heartwood and decline in concentration gradually towards the outer perimeter of the tree.

This link is a few years old, so ignore the comments/recommendations regarding CCA treated lumber, as it is no longer advised or available.

Here is a link that might be useful: native trees rated by rot resistance

Gardengal I am glad you posted that link, because it is an excellent example of the junk science she typically espouses and her lack of real-world gardening experience. Look closely at the evidence she offers: she couldn't find a study that proves an opinion opposite to hers; that's the reason. Nothing else. Just 'I didn't find a study'. No logic, no reasons, nothing (actually she did find just one relevant study, and it disagreed with her, so she dismissed it unilaterally as "artificial conditions").
It may be proven someday that cedar is not inhibitory to plants, I don't pretend to know, but it wouldn't make this any less junk science. Think about it logically, her proof can be used just as effectively to "prove" the exact opposite. Someone could say 'there is virtually no documented evidence for a lack of allelopathic activity in either Thuja or Cedrus spp'. It means nothing either way; only that there are more questions and that it would be eggregious for a PhD to call it a myth based really only on their personal opinions.

When I said "that link" I meant the one above to the Chalker-Scott article.
Btw Gardengal when you say that position is "backed by science", and you talk about "all evidence to the contrary", what science & evidence do you mean? I'm not disagreeing with you, I'm ready to believe, I'd just like to see the evidence. :)
- Tom

The chips tie up the nitrogen until they are decomposed. Sawdust does the same thing. If you use them, add some nitrogen to the mulch to help your plants along. I think you'll find your plants do a lot better.

BTW -- I'm in Salem, Oregon and would like to get a load of compost delivered. Can I get Bailey's here, or is that a Seattle thing? Any recommendations?

Rain I'm not sure specifically about cedar, but I seem to remember reading about research that showed the extra nitrogen usage was not signicant in large chips that sit on top the soil, as opposed to those mixed in. Does anyone recall if that is correct?
- Tom

Tom -- it makes sense. Large chips don't decompose as fast, so they don't suck the nitrogen away from the plants. Sawdust is the worst and needs the most nitrogen added to offset it. Mixing in the chips, whatever the size, will speed up the composition, too.

I believe the myth that cedar chips retard the growth of plants originates from the fact that very few plants grow under mature Cedar trees, Thuja plicata. The reason for that is the dense roots and canopy, not any supposed allepathic qualities of the tree. Few plants grow under Pine trees and yet the needles are used as a mulch without hesitation. Why should it be any different with our Cedar trees?

I have used Cedar chips for over 30 years and have found no difference with any other kind of wood chips as far as plants growing in it. Some tree chips break down faster than others, but they all do the same job protecting and improving the soil as far as I can tell. Walnut wood chips would probably be the only one I would avoid.

I have approximately 100 cubic yards of chips on hand now awaiting the Fall rains before applying. If I put it down now my plants won't get enough water until well after the winter rains have begun. This year that delay would be too long for the gardens well being. I really appreciate the rain we had last night, but it didn't penetrate very deep.
I'll take science over myth any day.

This discussion seems to have strayed a bit from the original topic. I apologize to the OP for the apparent hijacking......it was not intentional, but sometimes one thing leads to another and is worthy of further discussion :-)

Tom, I've made my thoughts on many of Ms. Chalker Scott's opinions pretty clear on this forum (and others) a number of times. I am not a big fan for various reasons. But I would not necessarily consider her 'myth busting' articles junk science. What is contained in these articles is a brief synopsis of her conclusions in response to these topics and yes, not documented by citations or attributions. But that doesn't mean the research hasn't been done or the scientific evidence doesn't exist......it is just not appropriate for that degree of detail to be included in a master gardener newsletter or extension service bulletin :-) But she is rather well-published in various scientific journals and has authored or co-authored a number of peer reviewed papers. For the most part, she's done her work. In some cases, I and others don't always agree with the conclusions reached, but the science is there.

As to the allelopathic effects of western red cedar (Thuja plicata), quite a lot of research has been done. Allelopathy is quite the 'hot' topic in various horticultural circles due to the potential of these natural plant chemicals to effect plant growth and thus be useful as natural herbicides. And of course, forestry management organizations are very interested in this phenomenon as regards its implication in affecting or perpetuating healthy forest systems. I'm not going to take the time do the research for you but it's out there. Much of the online material is available only by accessing paid subscription scientific sites like springerlink but there are some accessible publications. And various scientific journals and texts are available at the library at CUH.

And the literature does support her contentions - there is virtually NO scientific documentation of WRC being allelopathic. E.L. Rice, who has authored perhaps the most conclusive treatise to date on allelopathy, states a slight effect from WRC litter but no indication of the roots or other tree parts having this property in any significant concentrations. And while there is far less documentation of research conducted on mulches specifically, it stands to reason that if the tree itself does not demonstrate allelopathic properties, the mulch is hardly likely to.

I think a lot of the confusion that arises regarding the "toxic" properties of various mulches has to do with how wood mulches act in a garden setting. And the nitrogen unavailability or tie-up they can create. Fine or shredded bark mulches or sawdusts can create a nitrogen imbalance at the soil surface. This is not an issue with established plants with well-developed root systems but can have an effect on the development and growth of seedlings or shallow rooted plants, as in many veggies and seasonal crops or plants. And there is a far greater chance of incorporation of the wood product into the soil with the necessary cultivation of most vegetable gardens, which will cause far greater and more widespread nutrient unavailability. I would not recommend this type of mulch for those situations for that reason. But not because the mulch itself is toxic or poisonous.

Botann, when you said "I'll take science over myth any day", I agree. What science?

Gardengal perhaps I could persuade you to read Ms. Chalker-Scott's article more closely. She does not say anywhere that research has shown cedar to be not allelopathic. Instead she says there "is virtually no documented evidence". It may seem a subtle difference, but it's really a key point. Here's an example of what I mean; look at these two claims; one is reasonable statement referencing other facts even though not cited, and the other is meaningless gobbledeygook (junk science) that would be irresponsible for a PhD to use as her only proof when publishing that a widely held belief is false:

1) 'the documented evidence shows there is virtually no allelopathic activity in Thuja'
2) 'there is virtually no documented evidence for allelopathic activity in Thuja'

I know it seems like nit-picking at words, but it is a very critical difference that can make things seems opposite to the truth.
The phrase she used, #2, as her only proof, could just as easily been used to prove the exact opposite. That's junk science and it won't change whether studies show cedar really is allelopathic or not.
When you say that degree of detail is not appropriate for her article, I must respectfully disagree. That would be true of the average garden article, but if one is claiming a widely held belief is false, you have to give some kind of evidence, even if it is a casual reference to someone else who has proved it false. This is especially true for a PhD; her ommission of ANY relevant facts when attacking a common belief was unworthy of her position at WSU.
-------------------
Completely separately now, I tend to believe it's very possible what you say about cedar, but perhaps you could find some way to convince a reasonable person? Look at the real evidence we have so far:
1) Chalker Scott mentions a study that found there WAS allelopathy in thuja against fir seedlings.
2) She also mentions research that shows Thuja contains a water-soluble tropolone inhibitory to fungi (mycorrhiza is a soil fungi vital to plant health?)
3) You mentioned a treatise by Rice that listed slight allelopathy in thuja litter. (No mention for or against for bark)
4) Abstracts I could find similarly mentioned allelopathy in the litter, and included statements like this: "the leaching of phenolics from the litter predominantly of tree needles, which remain on the ground for a longer time due to slow decomposition rate, are held responsible for these interactions."
(Obviously bark mulch on the ground for a a longer time is not natural & would not be studied by forestry interests.)
5) Beluga gave his personal specific experience and described a simple easy test with fir & cedar mulch you could try for yourself.
6) Even Chalker-Scott agrees that the widespread belief is that there is a problem growing healthy plants with cedar mulch.
7) You or I could find no factual references to contradict these above (same loopy logic used in Chalker-Scott's article).

I'm ready to be convinced, and I really want to know because I would like to use it myself. Do you have any evidence or know any relevant facts?
- Tom :)

OK......this is getting silly and very far from the point. Do the research yourself. As I stated, the information is out there if you are that curious or interested enough to search it out, but I wouldn't restrict myself to abbreviated online excerpts. You may actually have to work at it. Or here's a thought -- get some cedar mulch and try it out in various growing situations. But realize that the results you may conclude from this experiment may be influenced by an incomplete understanding of the soil/mulch interaction and its impact on microbial activity and nutrient availability. And how this interaction may have a much greater impact on certain types of plants as compared to others. Junk science is far more likely to be realized under this type of experimental process because of the lack of scientific criteria considered or followed -- I got this result, ergo this is the reason. Which is exactly what beluga reported. And the myth Chalker Scott was attempting to debunk.

Actually not far from the point at all. :) The original poster asked if there was a problem using a mulch mixed with cedar, which is exactly what we are discussing.
Remember the question is not just restricted to chemical allelopathy in cedar, but 'is there any problem with it?', so Beluga's simple fir vs. cedar experiment covers a wide range of possibilities. The exact reason isn't important to us, just 'is there a problem'? Because of the specific question it asks, it is valid experiment, even if you want to invoke "scientific protocols"... consider it more closely.
I'd be glad to pay for the full articles if I could find any that show what you are saying. Excerpts are the way that I find them (jstor, etc), is there a better way? I'd love to just trust you that they are out there, but you did originally use Chalker-Scott as your reference(oops)...
I also find it interesting that Chalker-Scott not only didn't reference any studies to support her opinion, she actually arranged her words carefully in a way that does not claim any studies support her, only claims that none yet are against her. Surely she researched her article? It looks like she couldn't find them either or she would not have mentioned 2 against her and none for her. But you are going beyond what she is saying, you are claiming that specific studies HAVE exonerated cedar from allelopathy. I'll pay for the articles if you can help me find them; I have looked. :)
- Tom

Actually, I have tried the experiment mentioned, if not inadvertantly. One year my usual source for pine mulch had already given it away to someone else when i asked for it. So I went to the local cedar mill and spread a few yards of chips 4 inches deep over our large strawberry patch. Done in late February. We harvested very few strawberries that year. It was mystery, until i started asking others what might have happened. They all said the same thing. Avoid Cedar chips.

I admit, that this is so-called anecdotal evidence, and the results would be much more conclusive had I, perhaps, tried both pine and cedar at the same time, mulching half the bed with one and half with the other. And maybe another bed with no chips.

Unfortunately for good science, I'm too busy gardening to waste my time encouraging a crop failure. I have a very big garden, and tend to use 5 or 6 pickup trucks of wood chips every season. Like everybody else where I live, I use any wood I can get, EXCEPT cedar. My California friends tell me Eucalyptus is far worse, and that walnut is about the same as cedar.

The rule of thumb seems to be: if nothing grows underneath the living tree, don't plant a garden beneath the same tree's chips.

Happy gardening.

I've mulched with fir, cedar, alder, cottonwood, hemlock, madrona, and eucalyptus chips and nothing seems to be able to suppress the grass and weeds growing under my shrubs and trees. As for vegetable gardening though I wouldn't bother with wood chips at all... to each his own of course but that doesn't really seem like a great idea to me because they just take too long to break down.

For the reasons that Tom already stated that article didn't to much for me. I really don't get why Dr. Chalker-Scott doesn't cite everything she writes that might be controversial. She is incorrect to assume her readers wouldn't be interested and could give herself a lot more credibility by doing so. Hey, I've got a great topic for her... no one has done a study demonstrating coconuts won't grow in Seattle, so I suppose you can!!

The rule of thumb seems to be: if nothing grows underneath the living tree, don't plant a garden beneath the same tree's chips.

And this is just the kind of faulty reasoning that perpetuates these myths! There are all sorts of reasons why plants fail to grow under the canopies of large trees but very few of them have to with allelopathy. In most cases it is because the larger tree creates a growing environment that is inhospitable for many plants: a) lack of sufficient sunlight, b) lack of adequate rainwater penetrating the heavy canopy, c) a very dense root mass that makes it difficult for young plants to become established, d) lack of nutrients and soil moisture because of the extensive tree root system hogging these essential items necessary to survival. To make the leap that because not much grows under large trees, the trees must somehow be toxic is to ignore the realities of plant growth and the requirements they need to thrive. A plus B does not automatically equal C! And to extrapolate this erroneous assumption into assuming mulches made of large trees that sheild out the undergrowth of many plants is also 'toxic' for that same reason just compounds the illogic.

Beluga, I have attached a link to a study done locally on various wood mulches and how they affect or do not affect the growth of plants. Of note is a excerpt regarding starwberries and their apparent sensitivity to bark mulches -- not because of any supposed toxic properties of the mulch but because of the nitrogen tie-up and nutrient unavailability: "However, research with strawberries showed that bark mulch depleted soil and leaf
nitrogen levels, and reduced yield." (Sonsteby, 2004).

http://www.ser.org/sernw/pdf/SPU_mulch_lit_review.pdf

Tom, if you really want to pursue this issue, visit the library at CUH or the Department of Forest Resources library at the UofW. They will have the scientific papers and articles that will hopefully address this issue in sufficient detail for you to reach some meaningful conclusions. I would also assume you could find some of the scientific papers authored/co-authored by Chalker Scott at these sources as well....perhaps they may convince you that much of the content of her published myth buster articles is supported by quite a bit more than 'junk science'.

I have also included a link that addresses the allelopathic properties of various tree species with supporting citations. You'll find that a great many different types of trees present some degree of allelopathy, some to quite a substantial degree. Many of these could very well be suspected of being incuded in arborist's wood chips available locally. However. WRC, Thuja plicata, is noted as having only slight allelopathic properties related to the tree's litter. At least this and the previous link may provide you with enough sources to at least produce a starting point from which to further your own research.

Here is a link that might be useful: Potential Allelopathy in Different Tree Species

Of course, the amount of shade generated by a big tree is going to stifle any plants that demand light. That is way beside the point I was making.

I don't quite understand how a set mass of cedar chips would take up more oxygen in its breaking down process, then the same amount of any other wood? Meanwhile, we all do seem to agree that cedar takes longer to break down, and because it has something in its chemistry that wards off the attacks of the usual micro-culprits. It's this function of an internal chemistry stifling growth, that worries me to use it around plants that I work so hard at, to get to grow. An idea verified by many knowledgeable locals, as well as my own experience.

I'm certainly not trying to rain on anybody's resource parade. Nonetheless, should any gardener ask me what i thought of using cedar chips, (which ostensibly the person instigating this thread did do) ... I would not hesitate to tell him/her to take care where ever they spread cedar chips as a mulch, especially in the veggie and the berry beds. if someone disagrees, that's OK, so long as i don't have to do it. For much the same reason I won't plant coconuts next spring.

One other point. Someone questions my use of wood chips, at all, as a mulch in veggie beds. My experience, is that if you mulch in the spring, as you plant, almost none of those chips will even start to break down over the 3 month Pac NW dry summer. And just about all of it breaks down over the long wet winter. So you have to start over again each spring. And maybe, with things like brassicas, you might want to add a little lime to sweeten the soil. It's about as convenient a natural process as any gardener might ask for.

Wow! Thank you all for your passionate responses to my post; I learned a lot from the discussion. To answer some of the variables, this mulch in question will be for perennial/shrub beds under big leaf maples (no conifers), so there will be no fruit or vegetables at risk. This week I realized just how much compost it will take to topdress all of my 1500 square feet of beds and I am now even more desirous of adding wood chips for bulk and longevity. I do not need the mulch for weed suppression as the beds are very densely planted, but to, 1) aid in water retention during the summer and 2) improve the soil layer in which my perennial and shrub roots grow.

Thanks to your comments, I feel like I have enough information regarding mulching existing beds, but let's address new beds (formerly lawn, from which the grass has been removed). This week I have been using this method for creating new beds: digging the dirt with a shovel (it really doesn't even deserve to be called soil), removing grass and rocks and breaking up chunks, then digging in approximately 1 inch of manure, 4 inches of compost, and some organic starter fertilizer to a depth of 1.5 feet, planting the perennial or shrub, then topdressing with a compost/cedar and fir arborist chip/organic starter fertilizer mix. Is there a better method to prepare ex-lawn for planting this fall? (bboy, I saw your note about amending holes, does that apply to amending whole beds too?) I'm trying to get everything I've bought in the ground instead of letting things freeze in nursery pots this winter (note: this would be a first).

Thanks to all for your thoughts. I'm in that phase of my gardening life where I know enough to be confused about everything. :)