Where Do Wood Chips Go?

This may be a dumb question, but I always wonder about it.

Every year I lay down a solid 12 inches of hardwood chips. Within a year it is down to about 4 or 5 inches, and if I let it sit for more than two years, it will be one inch. Eventually it is just gone. What happens to it?

I know there are air pockets, and over time the chips settle down. That accounts for some
I know it rots and crumbles, and turns into dirt, but shouldn't 12 inches of wood turn into more than 1/8 inch of dirt? That is my estimate for how much actual dirt is leftover after three or four years. A few years after that and it is totally gone, outright, like it was never there at all.

If you don't constantly add more chips, you eventually just go back to the same dirt you always had.

It just totally disappears. Where does it go? Are gremlins sneaking in at night and gathering it up?

Where do wood chips go?
Honest question

It may look like the same old dirt, but I would wager it's better than before.

Offhand, I would speculate that it's the same rule that applies to composting: a truckload of raw material equals a pail or two of finished compost.

I feel, for the most part, wood chips break down and return to the soil.

At our place, we put the wood chips on paths.  I find that they somehow work their way from the back of my house where the garden is to the front of the house.  Maybe they are carried away when we get heavy rain or when we have strong winds.

This is my favorite thread about wood chips so I hope you or other folks will enjoy it too.

https://permies.com/t/120453/Great-Wood-Chips

Some of it gasses off as CO2, but I have no idea what the numbers are. I have a pile of chips that was on our property (embedded in bramble) when we bought the place four years ago and it hasn't substantially shrunk, though the stuff at the bottom is rich humus. I wonder how much the answer depends on climate.

I agree - there's a reason why many experts are seriously concerned with the world wide depletion of topsoil due to poor farming practices!

1 inch (2.5 cm) of topsoil can take between 500[17] and 1,000 years[18] to form naturally, making the rate of topsoil erosion a serious ecological concern.

https://en.wikipedia.org/wiki/Topsoil

Topsoil is a mix of decomposed biological matter (organic carbon) from above and minerals from below. It takes about 500 years, in an undisturbed temperate forest or prairie, for natural processes to create one centimeter of topsoil.

https://sfbiochar.com/?p=en.topsoil

On the other hand, I've read about how quickly that can be turned around by farmers such as Greg Judy, Gabe Brown, Mark Shepard etc by using polycultures, mob grazing, low to no tilling, and most importantly, adding lots of carbon to the soil. However, are they actually "adding" inches of soil? Or are they simply turning poor soil into fantastic soil? Fantastic soil grows healthier plants and holds much more moisture.

So to answer the OP's question - it takes a lot of organic matter to build soil. Have you considered less wood chips in favor of living polyculture plants? Is rainfall washing away your hard won carbon? (big problem in my biome as we get rain all winter when there's not enough light for plants to grow... ) Or is your soil growing in depth downward rather than upward? Have you considered adding mushroom spawn to the wood chips to help grow soil that way?

Christopher Weeks wrote: I wonder how much the answer depends on climate.

My guess would be a pretty great deal. I don't think you can keep wood chips (uncovered, in piles) in the Southern US without them disappearing relative quickly. With our heat and humidity wood chips don't last long. Took me a while to make sense of this, there's lots of people that want you to believe wood chips is THE answer, it's just a part of it. Within a calendar year my piles have shrunk significantly and they are full of webs of mycelium and usually ants. If you have lots of active biology in your soil wood chips will disappear even more quickly, worms will come in and help. I've got a worm farm in my garden just by droppin chips everywhere. There are piles of wood chips/logs/sticks and leaves around all of my fruit trees... leaves will decompose quickly, wood chips/sticks relative quickly, and the logs will decompose slowly over a few years. (Michael Phillips bless) And of course there is charcoal in/around every plant hole I've ever made in the last 4 years.

We have a wood chipper that has been really handy but not the right tool to make enough chips for a few acres. If you plan on using wood chips for your garden make sure you have a good supply. I had a good ole boy dump a truck load of chips last year around this time and it lasted me an entire year and I've been able to mulch my beds, trees, my ole ladys trees and give some mulch to neighbors. But I'd need a dump truck load every year if I wanted to top everything off, which just isn't practical. But I'll take the chips as they come, as I can make them. They are an extremely useful resource. If I could have two piles that stayed topped off, I would happily choose wood chips and charcoal.

Good question by the way, OP. I would just say they get gobbled up by biology. That's how I would explain it to anyone that asked me, anyways. But what do I know?

Also, I haven't done the experiment but would like to just to observe on my own the difference in how fast difference types of wood chips break down. Side by side, huge piles, hard and softwoods. With enough gumption I'll make that happen and probably learn a great deal.

Christopher Weeks wrote:Some of it gasses off as CO2, but I have no idea what the numbers are. I have a pile of chips that was on our property (embedded in bramble) when we bought the place four years ago and it hasn't substantially shrunk, though the stuff at the bottom is rich humus. I wonder how much the answer depends on climate.

Exactly.  Don’t know the numbers either, but it is a lot.  Long seasons of hot humid weather oxidize organic matter very quickly.  We live in the Appalachian foothills, and you can readily see the organic matter in the soil increase as you travel to higher elevations with shorter, cooler summers.  Ways to preserve carbonaceous matter include submerging it underwater to exclude oxygen, turning it into biochar, and shading it to keep it cool.  Tillage of any sort accelerates the oxidation process.  Drying it out also slows decomposition, but not really what we want for food production.

This may be up for debate, but in these parts, trees produce significantly more organic matter versus grass.  The woodlands always have deeper, darker soils, than the artificially maintained (mowing/grazing) grasslands.  

Gray Henon wrote:Exactly.  Don’t know the numbers either, but it is a lot.

I believe it's about 95%. It makes sense, really. If it pulled most of its mass from the ground, it would sink an equivalent amount into the ground that it had pulled from it.

Where have all the woodchips gone? Gone to flowers, every one….

A new verse to a great old campfire song;)

Really though, much like water, the off gassing Co2 and other plant growth stimulating compounds is partially reabsorbed by plants above the decomposing mulch.  The higher and more complex the plant matrix from understory to canopy, the higher proportion reabsorbed. This is an under appreciated facet of why old growth forests not only sequester megatons of carbon and water, but also absorb more and more each year they grow and become ever more complex. In the our garden soil, fungi are also, but to a lesser extent, breaking down the woodchips to absorb their carbon and nutrients which are exchanged within the soil food web to grow more plants and other biota.

In a complex forest forest garden where biomass is kept on site, I would bet that the extra biomass accumulated on land covered in woodchips would be closer to the mass of the wood chips spread than one might think. The less permanent over-story and root mass we have, the less this would be true as erosion, leaching, and off gassing to the atmosphere increases.

Donning my teacher’s hat ……………….sorry but you’ll have to put up with me.  I just returned from conducting an evening beginners gardening class in town. I haven’t returned to "normal mode" yet.


"My mulch just disappears" is a very common statement I hear from novice gardeners. And my standard response is "you better hope it does or you’ll never get soil to garden in."

I live in the tropics, so we have year around decomposition going on. As a result, beginning gardeners are struck by just how fast their mulch or compost disappears. Some novices give up in disgust when they see their $300 truckload of mulch mostly vanish in a year or two. Others have enough curiosity to try figuring out what’s going on and what changes they see.

As mentioned already, coarse organic material has a lot, lot, lot of air space. As that fluffy mulch or compost decomposes, it loses a lot of the air spaces. So that’s one reason for the mulch layer getting thinner and the bare ground starting to show——or hopefully, the weeds growing up through the mulch. That’s far better than bare ground, believe me, though novices don’t think so.

Fresh organic material often has internal structures (think scaffolding) in leaves and stem, plus "water" in between those structures. As the scaffolding collapses, the leaves and stems flatten out. I use banana trunks as a visual example. People can readily see the scaffolding in the cross section of trunk and see the liquid running out of a freshly cut banana trunk. So…pile up a ten foot deep mound of banana trunks (covered up so that the rain cannot wash the material into the lava below) and you will end up with a couple inches of wet, blackish material after a year or two of decomposition. This is normal.

Losing air spaces isn’t the whole story. As long as the right microbes are present,  plus the soil stays moist much of the time, the microbes and fungi will be eating away at the organic material. The microbe "poop" gets eaten by other soil life, with eventually the plants benefiting along the way. The microbes include all sorts of soil life, and the more organic material present, this soil life increases, thus decomposition increases. But microbes alone don’t make your mulch disappear. There are a multitude of soil critters also at the mulch buffet. Not just worms, but also plenty of "soil bugs" and slime molds that novice gardeners fail to realize are actually beneficial and necessary for fertile soil. Millipedes, sow bugs, certain beetles, and plenty more. Dung beetles, earthworms, and ants actually transport lots of organic material underground. I’ve watched a wet pile of sheep dung totally disappear in 5 days! Just gone!  By disappear, of course we mean that it was transported underground.

As mentioned already, during the decomposition process, gasses are released, some of which end up in the air. CO2 and nitrogen are major ones that can gas off. So think about it, if you don’t have enough soil life and plant roots, you could be losing some of your precious nitrogen. Thus my comment about weeds……plant roots help capture that valuable nitrogen, plus provide a stage for decomposition by the soil life. In my opinion, a light growth of weeds is beneficial. Far better than bare soil. But weeds should not so thick as to hog the moisture and nutrients, thus crowding out your veggie plants.

If your mulch and compost don’t gradually disappear, your soil is in trouble. It doesn’t have the microbes, slime molds, fungi, soil critters, and moisture that it needs. Sometimes the soil pH can be way wacky and needs adjusting. Sometimes the mineral content is wacky. This is where a full chemical soil analysis becomes important.

Rejoice if your compost and mulches disappear! It means that you are improving your soil. But it is an ongoing task, one that can take at least 3 years to see significant visual improvement. Every year I apply generous amounts of compost and mulch to my soil. My soil keeps getting better and better.  And yes, it all eventually "disappears’ into the top several inches of my garden soil.

Su Ba wrote:Donning my teacher’s hat ……………….sorry but you’ll have to put up with me.  I just returned from conducting an evening beginners gardening class in town. I haven’t returned to "normal mode" yet.

What a lovely lesson Su! I think this is a lesson that new gardeners need to hear several times in various different formats before they realize the profound truth in it. Weeds are our friends (well, maybe not Himalayan Blackberry in the Pacific Northwest) and they help us even if sometimes we need to whack them down for the sake of what we want to grow!

Thank you, Jay. Yes, lessons are best taught from multiple angles. Not everyone learns or understands in the sane way.  Repetition is good. ……….. And weeds can be good. It is simply a case of too much of something that becomes a problem.

This is a lovely discussion.
My own experience is mostly with leaves.
Every year I fill new beds with autumn leaves, and a year later they are an 8th to a 4th of what they started with.
Spread out over a lawn and they decay with no noticeable increase in depth.
Woodchips have been much the same.
I now treat my walking spaces as places to harvest biomass from, rather than add biomass too.
Whatever grows in walking spaces is added to the beds as mulch.

If I get woodchips again, they will get the same treatment, piled 2-4 feet deep in beds and planted directly into.should
Potatoes and beans, mostly with no anticipation of a crop.
A year later and it should be fit for tomatoes, onions, etc.
The nutrients do leak into the surrounding soils, but I am planting comfrey a
ound the base of the raised beds to catch and recycle that bounty

William, I love using comfrey in the garden and grow lots of it. I have it growing around the perimeters of the compost bins and chicken pens. Plus in patches here and there around the farm. I suspect that it does indeed capture the errant nitrogen. I harvest the leaves by chopping off the entire plant an inch above the soil. It readily grows back. The leaves make a wonderful seed free mulch for around the base of veggie plants.

William Bronson wrote:This is a lovely discussion.
My own experience is mostly with leaves.
Every year I fill new beds with autumn leaves, and a year later they are an 8th to a 4th of what they started with.
Spread out over a lawn and they decay with no noticeable increase in depth.
Woodchips have been much the same.
I now treat my walking spaces as places to harvest biomass from, rather than add biomass too.
Whatever grows in walking spaces is added to the beds as mulch.

If I get woodchips again, they will get the same treatment, piled 2-4 feet deep in beds and planted directly into.should
Potatoes and beans, mostly with no anticipation of a crop.
A year later and it should be fit for tomatoes, onions, etc.
The nutrients do leak into the surrounding soils, but I am planting comfrey a
ound the base of the raised beds to catch and recycle that bounty

How do you get enough chips to get them that deep?

I've  used Chipdrop and made some local connections via Craigslist.
I haven't done it in quite a while, chosing to focus on leaves and brush instead.
I have some of these resources on hand and they need to be dealt with, so developing ways of using them is more useful than seeking out woodchips.
I could even see getting paid to remove leaves and brush as a seasonal gig.

Moving woodchips can be a challenge compared to bags of leaves or bundles of brush .
I might build a three sided corral of chainlink fence for the truck to dump into if I ever order anymore.
By shoveling the chips out if the way I could add a 4th side, and just use the chips where they are.
Chipdrop offers loads that include logs, very large ones.
If I had the wherewithal I would choose this option and use the logs to make beds.

If there were a simple way to burn or  pyrolysize arborist woodchips and capture the heat they would be way more valuable to me.
Unlike wood shavings or pellets,  they are pretty wet, and most reports I've read of using them in tluds or retorts have been negative.
The trench method seems to work on everything,  so maybe it would work on arborist woodchips.

Gray Henon wrote:
...
This may be up for debate, but in these parts, trees produce significantly more organic matter versus grass.  The woodlands always have deeper, darker soils, than the artificially maintained (mowing/grazing) grasslands.  

As you say, this is highly dependent on different factors: on the grazing management, the soil, which part of the organic matter is taken into account, etc.

To go back to the organic matter which decomposes: one way of making it stable, is by producing biochar. The Kon-tiki is a way of doing so

To not lose the carbon in the soil, keeping it covered and with living plants at all times is important.

The soil also has its importance: when the soil contains clay, the organic matter can combine with it, creating stable clay-humus complexes. In sandy soils, this isn't the case

Super excellent post!

Su Ba wrote:
If your mulch and compost don’t gradually disappear, your soil is in trouble. It doesn’t have the microbes, slime molds, fungi, soil critters, and moisture that it needs.

Or it just wasn't very biodegradable in the first place, which amounts to the same thing -- if it's not disappearing into the soil, it's not doing the soil any good, because whatever nutrients are in it are still chemically bound up and are not available.

Rez, you brought forth a good point. ….. not biodegradable in the first place. Can that be? Well, in a sense. If the proper microbes/fungi are not there in the first place, then the wood chips don’t decompose.

This point was revealed to me when I moved to hawaii. Back in New Jersey I used chopped wood bark, most likely pine, for my flower beds. Every year I had to replenish the beds a bit because the chunks gradually rotted away. Then I moved to Hawaii and promptly purchased bags of pine bark chunks for my new flower beds. 20 years later most of the chunks are still readily discernible !
They haven’t rotted away. So, what’s different? While Home Depot shipped in bags of pine bark, the bark did not have the species specific microbes/fungi capable of decomposing pine bark.  OR, if it did carry them, those microbes/fungi were not able to survive my Hawaiian soil conditions. Therefore, the microbes, probably a fungi, are not here and thus the pine bark does not rapidly decompose. I find this to be quite interesting. I had naively thought that any microbes/fungi would do, but in the case of these landscaping pine chunks, it hasn’t proven to be the case.  So in effect, the pine chunks are not biodegradable here. Interesting case.

A good example of how it pays to know what's native to your own conditions. Compost that vanishes overnight in the desert may last forever in Hawaii, and v.v.

I remember my tenant being amazed that in the desert, dog poop doesn't turn to white powder and disappear as it does in milder climes; rather, it petrifies.

Su Ba wrote:Rez, you brought forth a good point. ….. not biodegradable in the first place. Can that be? Well, in a sense. If the proper microbes/fungi are not there in the first place, then the wood chips don’t decompose.  

Yes, I've noticed the same thing only with me it's cedar.

All over the place, I see people saying things along the line of "don't use cedar near growies". If you live in an area with no live cedars - or even just a minimum number, I would agree. However, here on the Pacific Wet Coast, I'm surrounded by cedars. They're indigenous trees and the microbes and bugs have all adapted to the chemicals that discourage plant growth.

That doesn't mean that I'd use cedar chips in my veggie garden, however, I used loads and loads of them on a path up my back field where it got hugely muddy in the winter. I did this year after year. You can't even see the path this year. The grass and forbs have grown over the area and the chips have been turned into soil and the area's high enough now that last winter it didn't turn into a mud-hole.

It seems the old adage, "for every rule, there is an exception" includes permaculture!  

The opposite can also happen -- the chemicals that discourage competition only apply in the native environment. Case in point, black walnuts -- I read about how they kill off everything under them, but here in south central Montana, where they're not native and are a marginal tree, everything grows under them just fine.

I cut wood to heat with- nearly 100% oak and hickory. Also have a chipper that eats anything up to three inches .
I use the chips less (than an inch in size ) in my dear wife’s flower beds. They last about 2 year s and I move everything to the raised hugelculture beds  and replace with new chips. If I had a way to transport my chipper to the wood cutting farm I would shred the smaller stuff.

I have no clue about the chemistry but she likes the looks and I like the results. In my raised bed.

My wife and I had this discussion a few days ago.

Last year, we created a new garden space with at least six inches of mulch at the thinnest part. This year we walked out and realized that the mulch level was relatively level with the non-garden lawn.

We added more chips this year, about a foot deep, and every time we were getting tired and thinking about quitting at 6" or 8" we kept saying to each other "It disappears fast, another wheelbarrow load!"

When it doubt, I mulch it THICKER.

Timothy Norton wrote:When it doubt, I mulch it THICKER.

And then if you can, add mushroom spores. Local or imported, they will help bind and hold all the nutrients released by the mulch decomposing.

Gray Henon wrote:This may be up for debate, but in these parts, trees produce significantly more organic matter versus grass.  The woodlands always have deeper, darker soils, than the artificially maintained (mowing/grazing) grasslands.  

It's also that grass can grow on thin marginal soils (which also hold little water), while most trees cannot.

I see this right in my back pasture, which is pretty much whatever random trees and grass want to grow there. Trees seed here and there, but only succeed along the lower edge where the accumulated soil is much thicker (being downhill from the rest). Grass scrapes by even where there's so little soil the rocks poke through. Even sage rarely gets a foothold in that part.