Wood chips in compost and soil

idaho_gardenerDecember 10, 2008

Kris (kiddo_1) from Ohio mentioned in the thread about Christmas Desires...


... that wood chips seem to break down slowly in the compost pile, but break down quickly when used as mulch.

That observation has stuck with me and I'm going to try an experiment. I'm going to add a bunch of aged wood chips to a new batch of compost, and when the compost has finished, (except for the wood chips) I'm going to spread it on the top of a garden bed and pay attention to how long the wood chips last.

The theory here is that wood chips break down better in the mulch environment. I know that fungi feed on wood. This fall I watched in amazement as some black mushrooms pushed hunks hard clay soil off of the roots of a rose plant and 'bloomed'. I've seen mushrooms likewise bloom at the base of other tree trunks, so it's clear that fungi will feed on wood.

I doubt there's a Nitrogen deficit in my soil or compost. I use copious amounts of grass clippings and coffee grounds. So I'm not concerned about wood robbing the soil of Nitrogen.


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val_s(z5 central IL)

I'm not sure but might not a better experiment be to mulch with un-composted wood chips and see how long they last in the bed while seeing how long the same kind of wood chips last in the compost?

It seems to me that if you partially decompose in the compost pile first it would negate the experiment. Of course I could be reading your post all wrong.


    Bookmark   December 10, 2008 at 6:26PM
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Cornell has some good info on microbial degradation of lignin.

Here is a link that might be useful: The Effect of Lignin on Biodegradability

    Bookmark   December 10, 2008 at 7:09PM
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Canadian Cowgirl, Thanks very much for the link! This answers a lot of questions and gives me other ideas.

First off, there's a thread going somewhere where people are kvetching about the fact that the straw in their compost didn't decompose. Your link has the answer why. In a word; lignin. So, straw and wood chips would make excellent mulch because they decompose so slowly. But they do decompose.

That link also explains why wood chips decompose as mulch but not in compost. Lignin decomposes in an aerobic environment. Buried in compost is not the right environment for decomposition. Nonetheless, I will be 'salting' new compost with wood chips and then spreading that finished compost on top of my garden beds. It will serve as a mulch while the rest of the compost fertilized the soil.

    Bookmark   December 10, 2008 at 8:29PM
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LoL, I had to look up "kvetching", it's such a cool word! Deprived childhood I guess.


    Bookmark   December 10, 2008 at 10:26PM
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From the link cowgirl gave us...

"The differences between plant species is likely related to differences in lignin structure, with gymnosperm lignin composed of coniferyl alcohols, angiosperm lignin composed of both coniferyl and sinapyl alcohols, and grass lignin of coniferyl, sinapyl, and p -coumaryl alcohols."

I'm laughing so hard I'm almost crying...Is this english? Somebody just made those words up right? Man, if I could only work that into a conversation!

"physical grinding and milling", this I got. LOL

Thanks for the link


    Bookmark   December 10, 2008 at 10:37PM
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dchall_san_antonio(8 San Antonio)

Back in the early 2000s a guy came by here and reported that he had been mulching over his clay soil garden with several inches deep of sawdust for 15 years. He said the clay originally was ceramic quality stuff...something about a brick factory in his area. After so many years of mulching with sawdust he said his soil was so soft he could plunge his arms into it up to the elbows. He underwent considerable grilling by the people on this forum. His answers made sense. Turns out "up to the elbows" was not in a vertical sense but more of a horizontal sense. Still...that is more like mulch itself than soil. He said that at first the sawdust looked like sawdust for about a year, but after years of doing it, it decomposed much faster and he could apply several inches several times a year. Apparently what happened was that his soil developed a huge population of the fungi that decompose sawdust.

I don't know if that helps any.

    Bookmark   December 10, 2008 at 10:42PM
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kiddo_1(NE OH 5)

Well, I look away for a minute and here's a new thread! Glad to see that my observation is backed up by some pretty impressive 'lignin language'. ;-)

Yes, I, too, have observed that straw and plant stalks, especially the hollow ones, take more than a normal season to break down in my piles (which are only semi-hot, kinda like me. *grin*) I figure the stalks give the pile a little structure and allows more air into the pile.

    Bookmark   December 11, 2008 at 10:18AM
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BTW, I am of the opinion that although most of my compost is pretty well finished in the compost pile, I still have uncomposted material in my garden soil. So, having straw and wood chips in my soil doesn't alarm me. Perhaps it should, but it doesn't.

I also have uncomposted coffee grounds in my soil.

As I originally said, I'll be mulching with wood chips (and straw).

    Bookmark   December 16, 2008 at 5:04PM
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joepyeweed(5b IL)

I would bet that the first time he composts wood chips, it takes a long time. I would also bet that each time he composts wood chips, it goes a bit faster. That would be a great hypothesis to test. Too bad I don't have all the time in the world.

The same with mulch, I would bet that the first time you mulch with wood chips they will last longer than subsequent applications.

My supposition is that your pile and your soil will develop a microherd capable of consuming what is available to them. Once developed it becomes more efficient.

Its purely conjecture... but its fun to ponder the possibilities.

    Bookmark   December 16, 2008 at 5:25PM
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Yes, joepyeweed - that's pretty much the way things work.

'Microbug' populations flourish based on the 'food' available to them. No food for other populations? - they simply do not flourish. Still there, but 'quiet', and in limited numbers. Organisms can go 'dormant' and/or their spores simply wait (a long time) for the right conditions to 'hatch'. Microbugs have an INCREDIBLE reproductive capacity given the right conditions.

In layman's terms, the stalk of straw or branch of tree is made of cellulose (strong plant cells) held together with a 'glue' called lignin. The lignin is what keeps the cells together when alive - or dead.

Lignin is the toughest plant material to decompose (that I know of). Specialized bacteria/fungus eat that carbon-based material that use nitrogen as an ENERGY source to reproduce. And they are well-known to STEAL nitrogen from soil and kill plants. Lignin is THE nemisis of my compost production operation.

Want to do an experiment? Layer sawdust 3" deep around your favorite plant from near (not against) the trunk, to past the foliage perimeter - and see how long it takes before the leaves turn yellow from chlorisis - but remove the sawdust before those microbes kill the plant - and then replenish lost nitrogen. Different activity from bacteria/fungi that "eat" leafy material which is nitrogen-based.

Live leaves are a favorite source of NITROGEN - but the SAME dead leaves are a primary CARBON source instead. Everybody have that 'figured out' yet?

Same with straw/hay which was live "grass" - a nitrogen source - before it dried out (before the stalk became so hollow). Wood chips on the other hand, were never a nitrogen source - always carbon-based - but lignin doesn't care.

Nitrogen does NOT "decompose" carbon into any form. Ever. Microbes do. But 'technically', microbes don't 'decompose' carbon either. They change it anatomically like a horse changes grass into manure (not saying microbes 'poop', so don't y'all 'get technical' on me - or I'll 'warm up' my keyboard...

Sugars, carbohydrates/starches are 'food' for microbes and nitrogen/carbon are 'building-blocks' in the decompostion of organic matter - kinda like bees 'barf' to make honey out of pollen. In one end, mix it around and back out the same end...The "secret" is in the 'mixing' by microorganisms - and someday science is going to figure out how they do it with enzymes and other acids/proteins.

Another anology - plant a seed. It sprouts. That seed has sufficient STORED energy (in what form?) to produce a plant - BEFORE true leaves can begin photosynthesizing to make food for the plant to continue growth. Food that then goes DOWN to the roots, to be changed (bee barf), then goes back up - to make more trunk/branch cells AS WELL AS more leaves, combined with the nutrients and mositure that the roots provided. See? Simple.

It's a long story you can read about in big books - but to make a long story short - HUMUS is the desired end result of composting.
When the organisms that reduce the plant forms of carbon and nitrogen to the point it will no longer reduce, it is almost pure carbon. Called Humus. Which remains unchanged for hundreds, and even thousands of years. Most of your 'finished compost' is gone next year, because the C:N was off and the microbe 'mix' was not 'fed right'. Don't get me started...

Soil texture is permanently changed by composted organics, only by the volume/percentage of humus that remains. Lots of other charactistics of soil than just texture...
And the next best thing is, that which does NOT become humus - feeds our plants by microbes changing plant matter BACK into the forms that the previous plants 'ate', so it is available to new plants again. Microbes do that. Not plant roots.

You don't have to know all about how decomposition works to enjoy composting - anymore than you have to know how a car works to drive it. Just drive and enjoy the scenery if that's what pleases you.

Me - I'm an "organic mechanic" 'cause that's what I like (and learned at my daddy's knee). I want to know how the organic 'engine' works.

On the other hand, I like honeybees - and keep a hive - but I don't care to know how bees 'barf' the sweet stuff - I just like to eat it - but there are folks 'like me' "out there" than will tell you in gross detail...But you may not eat honey anymore after you find out. I put that book back on the library shelf after page 3.


    Bookmark   December 16, 2008 at 7:35PM
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I tried the experiment of sawdust and wood chips when I dumped some into a low spot in my lawn. I have been putting material into this low spot for a while and the grass is thriving.

The sawdust had no effect whatsoever.

I know this because I put it in the low spot despite having heard that you weren't supposed to do this to soil because it supposedly robbed the soil of nitrogen. I figured I'd take a chance and see what happens. Nothing. Nada. Zilch. Healthy grass. Maybe even healthier.

I suppose I should try a wholesale, blanket the grass with sawdust, experiment. If I get a chance, I will.

    Bookmark   December 18, 2008 at 7:17PM
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Here's a controlled test with woody compost that might be of interest.

Here is a link that might be useful: Composts as a Soil Amendment

    Bookmark   December 18, 2008 at 7:58PM
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What I have seen in my yard and garden over the years is that wood chips put into the compost mix will be (depending on size of the chips) digested in 6 to 12 months while the wood chips I plunked down around trees and shrubs are still in place and working at controlling "weed" growth, aiding in maintaining soil moisture, and aiding in keeping the soil cooler while adding, very slowly, some organic matter to the soil.
The thickness of the mulch, when it was applied 6 or 7 years ago now, was 8 inches and today it is about 4 inches and getting close to time to replenish.

    Bookmark   December 19, 2008 at 7:29AM
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led_zep_rules(5 WI)

At my last house I used wood chips on the paths between the rows of the garden. Fearing the wood chips and soil would get horribly mixed together, plus the dreaded nitrogen stealing, I put barriers such as bricks and boards between the wood chip paths and the garden rows. The next year I applied more wood chips. The third year I was going to do that again, but instead I wound up pushing around the top layer of wood chips and scooping up the LOVELY fluffy black rich soil that the underlying wood chips had become, and putting that on top of the garden rows. Then I put fresh wood chips down on the paths.

I tried to mulch around my current raised beds with wood chips over cardboard, but it always rots fast and weeds grow in it. So recently I just go with cardboard, as the wood chips make it rot faster. My wood chips always seem to rot pretty fast, maybe because it rains a lot here so they are soggy a lot? I put shredded branches into my compost because we get them from our chipper-shredder and have copious amounts of green that need some brown to balance it. I do use leaves mostly, but I like to use whatever I have and the branches are from my own property and organic, and the leaves I take from other people.


    Bookmark   December 22, 2008 at 3:54PM
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shebear(z8 NCentralTex)

From my observations at our community gardens if the wood chips are under 6", they compost quickly and if they're over 6", they take much longer. We have to compost our beds about 4 times a year to keep a 6" cover but the paths which are at least 9-12" deep only need a spring application.

    Bookmark   December 23, 2008 at 7:28PM
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Really, all this is relative to what KIND of wood chips are used. Some decompose MUCH faster than others, so it's not fair to compare observations using only "wood chips" as a determining factor.

More specific information would be more helpful. For instance there is a LOT of difference between composing OR mulching with a soft-wood (low-lignin) conifer, than with oak or maple.


    Bookmark   December 23, 2008 at 11:03PM
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I've been composting with a compost-tumbler for the past two years. I keep reading that in finished compost the materials composted will not be recognizable. When I think my compost is finished I can easily see the leaf parts and pieces.
The compost, as I do it heats up to about 150 degrees, stays there about a week, then drops to about 120 and continues to drop for another 4 or 5 days until it has no more heat. I assume that the batch is complete at that point. The whole process is only three weeks long at best.
I am doing this in the high desert of AZ where temps are around 100 in the day time.
Does this sound like I'm doing this correctly?

    Bookmark   December 24, 2008 at 1:01AM
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New wood chips, with lots of moisture, will perform differently than wood chips that have been aged, allowed to sit around and dry out, simply because of the moisture levels in those chips.

    Bookmark   December 24, 2008 at 6:50AM
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Ok, rewarming this subject because I have a new toy; a Mackissic Mighty Mac 12p chipper/shredder. The emphasis is on the shredder, but the chipper is important, too.

The shredder is a hammermill type - it pulverizes stuff until the stuff is small enough to pass through the screen. The output looks like chainsaw chips.

Shredding fresh branch trimmings makes a very hot 'compost' mix. Very hot, very quickly. Very nice.

But I suspect that it will take over a year for this type of compost to 'finish'. That's ok, I have other compost, but it will just take that much longer to discover its characteristics/qualities.

I also have a bunch of pine needles to grind up. I'll be using most of that for berry bed mulch. But first impressions of ground up pine needles is that it might make a fine compost ingredient. I'll know more soon.

But getting back to the original subject, I'm aiming for a high-lignin mulch/compost to condition the clay soil of my garden beds. Softwood tree wood will be the primary sources and I'll use as much green wood as I can to give it a compost start but aiming for a fungal finish.

    Bookmark   July 27, 2009 at 1:10AM
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I red one article where the technology of chipped wood include inoculation of it with the forest litter. Chipped wood is not composted but is spread on the soil with 1cm height. Then it is digged in the soil slightly 5-7cm. Then it's necessary to grow legumes 1-3 years. After that soil can be fertile during 10-15 years.

    Bookmark   July 27, 2009 at 4:24AM
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