concerns with using cardboard/newspaper as a mulch

Any soil test results?

I would never use these chemical laden paper or cardboard.
I don't even use the ashes from my wood stove if it has been started with such.

We have been using waste boards that come off of my sawmill.
There are plenty of them and they work well when lined up edge to edge.

They are culled boards because they warped or have other defects. 
Wood chips can go over these.

next spring I am going to drill holes in these boards to put the plants in.  That will hopefully make for less weeds.

Great thread!
We just laid down a few smallish sheet-mulch blankets in our garden being prepped for a long permaculture project. We clearly have the residues of non-organic practices by the previous owner, but reading Paul Stamets's Mycelium Running gave me hope: he considers fungi as the spiritual sentinels of Earth, and they indeed break down organic toxins and render metal contaminants less harmful—the mechanism for the latter is not delineated in the book. (Alkaloids in plants are the reservoirs of metabolic end-products: they are intracellular, inert crystals.) We need more research.

I think I will do a little private investigation in the Spring and will do comparative soil analysis from under the sheet-mulched area (a variety of paper was used). Of course, it may be inconclusive since the paper-mulch was not tested for toxic additives before it was laid down and a truly detailed analysis is probably expensive. Still, Paul (and Geoff and the Almighty Sepp) may have good reasons not to be terribly concerned about paper-mulch contamination.

Never ever ever ever had a problem with card stock/board as base layer... I've done a couple hundred sheet mulched beds now. Never an issue. But sure, use common sense..Rip tape/adhesive off.
Peace -

I made my own laundry soap and started with home made lie from ashes.  I read all the material and warnings, but I too never had any problems with it, I could put my hands in it, etc. I just didn't let it sit long in it's pour form on skin or clothes.  I was more afraid when I used store bought lie.

Let me see if I remember....... I think I could get two batches from one load of ashes.  Heat on the stove, very hot water and stir while they 'cook'.  Then let 'em sit in a bucket for a couple of days (24-36 hours) and they settle to the bottom, pour off the clear-ish liquid on top, add water and make another batch on the stove.  I really don't remember the details off the top of my head, I'll have to see if I can find my notes.  Anyway, my method was a lazy version of how they officially did it in days gone by with a fire, cooking and filtering.

I then used this liquid in the standard home laundry soap recipe with Naphtha soap, washing soda and something to soften the water.

I don't do all this any more as my very hard city water really worked against me.

But making your own lie water is easy 

Podcast review of Geoff Lawton's Urban Permaculture DVD: podcast

Paul explains his preference to not use cardboard.

This well laid out, comprehensive article adds to our research into the topic. Is newspaper toxic to your garden

Living Wind wrote:Never ever ever ever had a problem with card stock/board as base layer... I've done a couple hundred sheet mulched beds now. Never an issue. But sure, use common sense..Rip tape/adhesive off.
Peace -

Have to ask, how sure are you that this has not affected your soil, deep down long term. I am not a purist, more of a researcher seeking to find the truth. So, my question is really 'have you done a before/after test of your soil for toxins? I think that we are a pioneer generation and that many of the things we are struggling to evolve will prove guideposts for those coming after us. We are setting the scene for a permaculture world.. and if you're like me, you'll be impatient for it to happen and struggling with your own 'trespasses' and inabilities to be permie-pure in varying degrees!!! All we can do is try... and whatever you are doing Living Wind, I salute you for your amazing efforts. We just have to keep exploring, keep examining new evidence and changing what we do as well as we can.. balancing the effects. Your food is likely zillions of times less toxic than store bought.. I know that what I grow, whilst not in perfect soil, yet or completely devoid of some contaminants [it was a lawn before our tenure] is way better and less toxic to our bodies and the environment than that other stuff!

In my opinion, if one quarter inch thick cardboard is still intact after 5 years, the tree was obviously not getting enough water or attention in general. I've mulched with cardboard and newspaper for decades and have never had a problem with it. A healthy microheard can remediate just about anything, other than heavy metals, so unless cardboard and newspaper are loaded with too much heavy metal, I just don't see any issue. In my humble opinion.

Nick Garbarino wrote: A healthy microheard can remediate just about anything, other than heavy metals, so unless cardboard and newspaper are loaded with too much heavy metal, I just don't see any issue. In my humble opinion.

Nick, what is a microheard? I want to know about anything that can remediate just about anything!!!

smiles
sunny

Hello Sunny. So, a microheard is a nice short term for all of the microorganisms that make up a soil foodweb. That's bacteria, fungi, protozoa, nematodes, arthropods, and others. This is the cast of characters that work behind the scenes to make all of our plants grow. Without them, nothing would. When soil is full of nicely decaying organic matter like we organic gardeners and permies like to use, then the microheard is really healthy, robust, and it can really take on all comers. You know, it was naturally occuring marine bacteria that actually cleaned up the great majority of the BP oil spill in the Gulf of Mexico. And they are still there, waiting for another big opportunity to do their thing. The microheard really takes good care of us, and we need to treat it kindly. A great book on soil microbes as it relates to gardening is "Teaming with Microbes" by Lowenfels & Lewis. Have you ever noticed little tiny springtails hopping around on some nice compost? They're near the top of this food web, and their presence means that you made some great compost. Of course, earthworms are great indicators of the strength of your microheard too. Keep smiling!

Nick - is this microheard the Who that Horton Hears, or were you looking for micro-herd, which seems more like it makes more sense for what you are describing?

If the paper/cardboard isn't rotting, you need nitrogen and/or water (and some fungus would help, but they will find it soon enough if you make it nice for them.) The biggest "issue" with paper is that it's a substance that easily mats and has about a 400:1 C/N ratio - it needs help to rot.

The whole smear about one paper mill's pollution: well, that would be relevant if they were making special-purpose cardboard for mulch. Which would involve all the same nasty "scary" chemicals, because that's how papermaking happens. Since they make cardboard for boxes, and then the boxes become solid waste if they are not reused, irrelevant. Also damning whole industry with presumably the worst mill they could come up with. Go throw away all your books and stop using paper and things that are shipped in paper boxes (so, no computers or e-readers for you - oral tradition all the way) if you really have a bone to pick with the paper-making process. Don't forget your certified organic non-GMO corncobs, because you wouldn't want your nether regions to touch chlorine-bleached TP that was made by pulping trees in hot caustic (sodium hydroxide!) solutions. Yes, there are a variety of things that you don't want to get into in a paper mill - and essentially none of those go out the door in the end product. They actually strive to reuse most of them in-house - it's good old-fashioned economics. Not only do they, in fact, get fined if they exceed their permitted discharge, they also have to buy chemicals, and the more they can turn them around in-house, the less they have to buy as well as the less they are releasing.

As for my garden, free paper beats $5/bale straw 8 days a week. I probably get more pollution on my garden from coal fired power plants in the midwest than I do from newsprint and cardboard. Should I put up a greenhouse using petrochemical plastic or high-embodied energy glass (wait, the mica greenhouse - just the thing!) to keep the rain off so I can filter all the water before it reaches my garden? What about the air - perhaps I should filter that too? Sheesh. All those filters will probably be made in plants that pollute and use chemicals, and then they'll be shipped in cardboard boxes, and....

I'm actually playing with making some thick cast paper "tiles" for paths and around trees, as something that will stay put without needing stuff piled over it to keep it from blowing away. That will be repulping newsprint and egg-carton type material, if it works (I'm not going to be running that much paper through a blender, which is the "usual" home-made paper technique for repulping) and does not require too much effort. Try not to wake up the neighbors when being permaculturally pure in your outhouse - corncobs are bit on the scratchy side, the old-timers say - they thought the Sears-Roebuck catalog was a big step up.

Ha ha. Nothing like a little comedy in the morning. Micro-herd is probably a better way to spell it, but I've seen it in print as microheard, microherd, micro herd, micro-heard and micro heard. Then of course there's always the term "bugs". All in know is cardboard works well for smothering grass, dog fennel, etc and it's often sitting by the trash can ready to be put out at the curb, and by using it I don't have to go to Home Depot for Roundup, breathing the ozone in the city, and burning fossil fuel and contributing to climate change, and spending money contributing to a disappointing Christmas. Uh oh, I used the r word back there. This might start another whole new thread.

Not a question or an answer:

I had a high school chemistry teacher who had previously worked for Tacoma Simpson Craft. He started his story about his previous job by taking a piece of paper from a random student, folding it into a simple pouch, and then pouring quite a bit of water into it. He said his job had been to make paper more water proof. He did not go into what that entailed. I think he drank the water though.

paul wheaton wrote:This would be a good time to point out that one could create cardboard using 100% mechanical means, plus using organic corn starch for the glue.  So, I suppose there could be something called "organic cardboard".  Further, as Paul Stamets points out, the seeds of edible plants could be worked into the cardboard.  So when you get a package, you can bust open the cardboard and then toss it out on your lawn.  A few months/years later you can have all sorts of fun stuff growing there!

yay i love this =)

yes you can do this, i have done this, and people do in small scale production. i have made paper, something thick like cardboard, and even seed paper.
actually have considered i could probably make some money if i were to explore paper making again, but i get distracted among my many crafts...though this is one i have been wanting to get back into. it was one of the more profitable crafts that i did for money, but this unfortunately isnt saying much!
especially with the seeded paper, i think you could make that profitable but the paper would be expensive. and you could send a card to someone and then they could plant it =)

one of the issues here is that we use wood for paper making, because its a material unsuited to being a fiber it actually requires a lot of nasty chemicals to turn it into a smooth paper. o and theres lots added that arent needed, too, but the main problem is in using wood at all. of thousands of years of papermaking wood wasnt a fiber used for this purpose until only a couple hundred years ago. and even then it was considered inferior to other materials until a chemical process was invented, and grinding machines made it possible to mass produce wood pulp for paper. though people are so accustomed to wood being the fiber used for paper, as being THE paper fiber, it really sucks as a paper fiber. it becomes fairly obvious if you look at it, and think on it...if you wanted to get a bunch of fine particles all smooshed together...would you choose some thin stalks that break down fairly quickly and easily, flax for instance, or a large solid thick felled tree???

..but to be true when i was doing lots of papermaking and book binding, it was kinda difficult to find buyers who were willing to pay the extra money for a quality product like this...as paper is so common and cheap and many people didnt seem to care about the organic and non toxic aspect...though some would get into the "tree-free" aspect. it really is expensive paper/cardboard for someone to actually make a real wage with this craft if they are making handmade paper. having a larger set up, a big beater, a crew...setting it up as a small industry, working in large batches....would lessen the time involved and help make it a little cheaper, still its much more expensive, and the people making it would not be able to be paid much. we did so anyway, one of the communities i lived at was for papermakers and book binders, we used lots of different fibers, waste fiber from plants, sometimes plants that were cleared were put in (small percent, then with a good paper fiber in large percent)
and even made sensimilla paper (instead of "hemp") with free leftover stalks from the production of the medicine. in northern cal this was an abundant free source of fiber.

sort of off topic, a bit of a ramble there, but i felt inclined to share that.

on topic- i love sheet mulch, it works so well. i love the results. i love how the worms love it, and i love how its a free surplus material that people can get easily to add to their gardens. thats where all the nutrients have gone, this sucks! that our forest has been turned into cardboard and all the nutrients that got locked into these cardboard boxes! so no...not ideal for sure...but since it is that way, we can at least put them back into the ground by sheet mulching with cardboard, which as a bonus is free, easily obtained anywhere, blocks weeds, and makes worms happy.

also as been said, its not enough by itself, you do this in conjunction with other mulch/compost/straw/wood/grass clipping/manure/etc
i make these cardboard compost sandwiches, it seems to work well, placing unfinished compost in between two large sheets of cardboard, then putting mulch/straw/etc on the top of that and planting there.

it totally depends on your rainfall though...if you dont have the rainfall like we do here you have to seriously drench it constantly when its first getting going, other wise its not effective.

as far as the chemicals and such...i dont think that over all it is very much ...imo it dissapates and works itself out in the soil ...the worms probably also help work that out... but yes there may be some very small amount o weird stuff going on there...this is nothing compared to the pollution of its production. so the paper mills are very toxic, for sure, the chemicals shouldnt be used, for sure, and not ideal, wood pulp shouldnt be used at all. but considering this is how things are, this is whats available and being wasted, i think its a good thing over all and dont think the small amount of funky stuff in the cardboard makes a huge impact, though its best to use the plain boxes.

I got a bunch of cardboard without any ink on it from the local organic supermarket. Also took the labels and the plastic tape off, so I guess I minimised the risks. Sheet mulched with it, and threw a load of horse kaka, sourced from the nearby stables, on it. Fluffy soils in spring here I come

Hi Pam ,

I remembered reading about the mushroom detox thing and found the link to the post here
https://permies.com/t/1428/fungi/paul-stamets-saving-world-ways -

This is Rose's post explaiining it - the toxins are broken down molecularly and no longer exist

Well, to mention one case of detox, Paul Stamets says that oyster mushrooms, undo, dissolve or whatever, bonds between hydrogen and carbon in carbohydrates, bread for example and so why not get them to do the same with petrol a hydro carborate. They did and in a competition to clean soil between bio nerds filling the petrol filled earth with bacteria and some other nerds, it was Paul Stamets who won, he put oyster mushrooms to work on the petrol soaked soil and his fungi really turned petrol filled earth into beautiful top soil covered with mushrooms, that then died, which the insects then came and ate, which insects the birds came and ate, leaving plants seeds behind, so the earth then bloomed with plants.
Put Paul Stamets name in youtube and you can find several videos of this happening. Read his book and you can find out how to make fungal mats which will clean soils air etc. He writes well, its a very easy read.

Most inks used by newspapers are soy based which are non-toxic. Newsprint's are not bleached but bleach paper stocks are not toxic. Corrugated cartons are made with starch glues that comes from plant starch like corns.They are 100% biodegradable and non-toxic.

I'm not encouraged by soy inks and corn starch glues, since the grand majority of both corn and soy are GMO in the US.

I'm surprised that this has not been posted in this thread yet.

It seems to have come up more than once in the last week.

Our dear friend Kelly Ware posted this on Facebook:

Now I understand why Paul Wheaton hates using cardboard on the garden. It is often laced with fermaldehyde if it comes from China ( usually more flimsy or says made in China) this pile was pulled out of my sister's garden after three years used for mulching under straw and wood chips. Not one wormhole nor any fungi at all grew on it. She too hates cardboard in the garden. I was awestruck by the total in-biodegrability of it

Plus this close up also posted on Facebook:

Chinese formaldehyde-laced cardboard. three years in the garden, no signs of wear.

Wow, that's amazing. While I understand that I'm in a tropical region where it can make a difference, cardboard doesn't last more than a few months in my soil. When using cardboard to smother grass, I cover it with 2" layer of manure/compost or a 6-8" thick layer of fresh grass clippings. Perhaps that also makes a difference. Anyway, after six months the only cardboard pieces that are recognizable are parts that were on the surface where the sun dried them out. If I had been diligent to cover them with compost, then they would have degraded too, in assuming.

All I can say is....wow.

At the risk of sidetracking this thread, I thought I'd post here since it's been quiet for some time, and I think it adds to the discussion.

The risk of formaldehyde contamination from cardboard in sheet mulching has been well and truly discussed. What I have not seen anywhere is a discussion about using this same cardboard as a growing medium for mushrooms.

We know that mycelium are very good at absorbing toxins, and corrugated cardboard is a widely used growing medium for cultivating oyster mushrooms and other culinary strains. I know Paul Stamets hangs out in these forums sometimes, and I'd love his take on the implications of this.

[Mod, please move this to a more appropriate thread if you think there is a better place for it.]

Nick Kitchener wrote:The risk of formaldehyde contamination from cardboard in sheet mulching has been well and truly discussed. What I have not seen anywhere is a discussion about using this same cardboard as a growing medium for mushrooms.

We know that mycelium are very good at absorbing toxins, and corrugated cardboard is a widely used growing medium for cultivating oyster mushrooms and other culinary strains.

People seem to assume that failure to decompose is direct proof that Formaldehyde is present in a sample of cardboard. Firstly, we need to be much more concerned about its persistence in the air of our homes. If my cardboard actually did have Formaldehyde in it, then I would want it OUT of my house. I'll gladly place it outdoors where it can off-gas! But secondly, and more importantly, try researching the chemical itself. How does the compound react in the environment? "Given its physical-chemical properties, formaldehyde is degraded by various processes in air, with very small amounts transferring into water. When released to water or soil, formaldehyde is expected to remain primarily in the original compartment of release, where it undergoes various biological and physical degradation processes. Formaldehyde is not bioaccumulative or persistent in any compartment of the environment." - https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/ewh-semt/alt_formats/hecs-sesc/pdf/pubs/contaminants/psl2-lsp2/formaldehyde/formaldehyde-eng.pdf  (page 49)

I don't particularly want any extra exposure to it than is necessary. Even still, I'm not going assume that few poorly decomposed cardboard sheets means there is a highly concentrated level of Formaldehyde that has stalled all biological activity. That's completely baseless. "Low levels of formaldehyde occur naturally in a variety of foods, such as fruits." - https://www.atsdr.cdc.gov/ToxProfiles/tp111-c1-b.pdf  So should we stop composting old fruit for fear that we'll disrupt the ecosystem?

If you want the cardboard to break down you have to water it when you lay it down, otherwise it will not break down easily.

I came across this, which I thought was relevant to the discussion.

Formaldehyde is not expected to adsorb to soil particles to a great degree and would be considered mobile in the soil, based on its estimated Koc. According to Kenaga (1980), compounds with a Koc of <100 are considered to be moderately mobile. Formaldehyde can be transported to surface water through runoff and to groundwater as a result of leaching. Parameters other than Koc affecting its leaching to groundwater include the soil type, the amount and frequency of rainfall, the depth of the groundwater and the extent of degradatio n o f formaldehyde. Formaldehyde is susceptible to degradation by various soil microorganisms (U.S. EPA, 1985). Howard et al. (1991) estimated a soil half-life of 24-168 hours, based on estimated aqueous aerobic biodegradation half-lives.

http://hc-sc.gc.ca/ewh-semt//pubs/contaminants/psl2-lsp2/formaldehyde/index-eng.php

I've always been confident that chemistry and microbes will denature anything but heavy metals.

So, what about heavy metals? I understand that there is some significant traces of many heavy metals in cardboard itself, plus a greater concentration still in the inks.
In addition, recent studies have found some leaching of those metals into food packaged straight into a cardboard box (such as oats). (I can't find this study, but it was from Germany and I read it only a month ago.)

Not the above study, but a reference to an earlier incident in the EU: Packaging Chemicals

the chemical 4-methylbenzophenone,  this component of printing ink had slipped from the outside of the cardboard box and into the cereal. That is, until the European Food Safety Authority (EFSA) was asked to look into the matter.

Study of cardboard colorants and heavy metals

Study of cardboard colorants and heavy metals

In this study provided by Jondo, heavy metals are found in cardboard: 2.6 mg kg-1 Pb (lead), 2.8 mg kg-1 Zn (zinc), 0.094 mg kg-1 Cd (cadmium), 1.8 mg kg-1 Ni (nickel), and 25.4 mg kg-1 Cu (copper).

This is indeed rather alarming, as I was planning to make cardboard a large part of the feedstock for a worm composting system. This would put a lot more of the metals onto land than using cardboard as a one time mulch. (I'll have to say here that I don't actually find cardboard to be a very good mulch, for other reasons.)

However, I do have two questions about the above findings: 1. What do these numbers translate into as far as ppm in the soil (in other words, how many tons of cardboard would have to be applied per acre to raise the levels significantly) and, is US cardboard different that the Turkish cardboard used in the study?

Also, I wouldn't worry about zinc and copper, since they are, in small amounts, beneficial elements, and they level of cadmium is quite low.

I'll do some more research on those questions, and if I find answers I'll post them here.

If I've done the conversions right, 1 ton of this cardboard would contain 0.005758474288 pounds of lead, so a thousand tons of cardboard would add five pounds of lead to the soil. (Feel free to correct my math, I'm terrible at it!) Again assuming I'm converting properly, this will raise the lead concentration by 2.5 ppm on an acre of land.

Below 100 ppm of lead in the soil is considered safe, below 400 ppm needs cautious gardening, over 400 ppm the soil should not be gardened. Soils I've tested have usually had around 20-30 ppm. Thus to raise them to above 100 ppm, many thousands of tons of cardboard would be needed.

A thousand tons of cardboard is (roughly) a hundred thousand cubic feet, or roughly an acre covered two and a half feet deep in cardboard. That's some sheet mulch!

I think cardboard with tape removed and black and white newspaper is fine.  Color in newspaper is bad news.  The black and white has soy.  Possibly the color cardboard is not great for the same reason.  They use chemicals to produce the color.

I worked in a box factory for 6 months here in Oz. Flat packed box pieces loaded by hand in one end of a machine, glued and folded mechanically, stacked by hand onto pallets then wrapped and fork lifted away. Worst job I ever had because of the tedious monotony and meaninglessness of it (packing fruit in a pack shed at least involves food directly) I got incredible arm muscles though from loading as many flat packs as possible at a time, and doing estimated 2,000 squats a day while lifting was fantastic for my back and legs too, so yay serotonin from exercise but boo to mental non-stimulation.

I asked someone there about this additives in cardboard issue/question.

The head engineer did his apprenticeship down south for 3 years in a paper mill.
Where the cardboard was made from trees.
Trees grown in plantations (I presume pine, as it is in kiwi land, but can't remember if he knew actually what trees were used nor if it was more than 1 type.)
The trees were loaded into GIANT shredders ("each as big this whole box factory" and that was a BIG shed) and blended up.
Then, with just water added, made into pulp. and into cardboard in other machines.
Definitely no other things put in there.
I asked about the dyes in the print, and the glues added in the box factory, his reply was " I only worked in a cardboard factory, not a printing or glue factory." Funny guy.


The above story of boxes from China not breaking down makes sense. I guess in Oz they have lots of room for "forests" so they don't need to use plastic in the cardboard. It burns clean, and breaks down fine that I have seen.

The glue issue, some boxes (not the flash ones we were making though) have only a single line of glue and no print. This would be easy to cut off. The glue will be whatever is cheapest, so the cynical me thinks abattoir discards (bones or skin boiled down for gelatinous substance?) but the brainy me thinks plant waste (corn stalks [GMO], sugar cane bagasse [i could ring a local sugar mill in the season and ask where their bagasse goes]) because its waste/free/easy to deal with.

paul wheaton wrote:
Another problem is that newspaper/cardboard tends to not break down particularly fast.   And  since the mission is usually to smother something that is already there, it is placed in sheets.  If too thick, it could make a layer that cannot be penetrated by water or air - maybe for many years. 

I've never had issues with cardboard or newspaper breaking down properly.

paul wheaton wrote: Last spring I visited somebody's garden where an apple tree was doing poorly.  After digging around a little, a layer of newspaper was found about an inch under the soil.  It was about a quarter of an inch thick and had apparently been put down to kill weeds about five years earlier.  It killed the weeds.  And it was making the tree sick.  And it wasn't breaking down.

Seems like a post hoc fallacy to me. Further testing would be required to see if it would in fact damage the tree. I've also never had this issue, but I have seen apple trees dying due to poor soil drainage in heavy soils. This could be the problem, not the newpaper, which would explain why the newpaper didn't break down; no microbes where available to do so. Once again TESTING IS REQUIRED. Our speculations have no scientific merit.

Leah Sattler wrote:I prefer hay for alot of reasons. for me most of it is just practical.

Same here.
We love hay and use bailed green alfalfa. It smells so sweet when you spread it. It builds up successively decayed layers and makes the soil spongy.
Everything combustible goes into the wood stoves to start fires. Then the ash goes into the poo composters and the garden.

I placed cardboard down under about 6" of mulch in the front yard about 2 years ago. We got very little rain, just under 3" in the first 18 months, and the cardboard was still looking new for over a year. In the last 6 months we've had about 17" of rain, almost twice as much as normal, and the cardboard has mostly dissolved as a result with lots of happy worms underneath.

I did discover that the cardboard boxes I used had a fine plastic mesh built in so as I was digging holes for new plants, I was hitting this mesh with every scoop. So I would suggest testing any cardboard you use first, tear each box a bit and if it's too tough to tear, there's probably some unwanted extras hidden in the layers.

Kabir424 Hatfield wrote:I live in Alabama and I have used cardboard on a couple of different occasions to kill off grass and add carbon to the soil. I usually just lay out cardboard from boxes with all of the metal and plastic off and then top that with leaves, compost, grass clippings, etc. This has happened on 2 separate occasions when I start this in the early fall and then by early spring I can dig these areas up to mix in the organic matter. The cardboard is still recognizable as cardboard but it is easy to rip to pieces and include into the soil. One year later I haven't found any pieces of cardboard in the soil because it has all broken down. I don't know if this is because I live in Alabama and we have such a long time period for things to break down or if its because I have overly active soil buddies or if it is something else. But, I haven't really had a problem with 1 layer of cardboard breaking down within a year and a half. This doesn't address any issues of toxicity leaching from the cardboard if there are any.

I think how "brittle" the climate is might definitely make a difference as far as whether the mulch breaks down quickly or might become a stifling layer. We've used sheet mulching (usually cardboard with woodchips or straw on top) at pretty much every farm I've worked at -- around the Great Lakes, upstate NY, north-central CA, and southeastern U.S., and never had a problem with it not breaking down. In one garden, we would sheet mulch probably a half acre with newspaper, three sheets thick covered with hay from our fields, and cut holes into each seedling when transplanting. It seems an incredible tool for establishing a new area, especially with a lot of more perennial weeds and/or woody stumps and residue, as well as around perennials, especially those with roots close to the soil surface, where weed control can be pretty tricky. When removed, generally reveals rich dark soil and awesome fungal activity. The one occasion where I saw it fail miserably was at a garden in Santa Fe. NM. In this harsh dry climate, it just sat there and fossilized -- we were still finding chunks of cardboard and dessicated horse manure in beds they had initially tried to prepare through sheet mulching four years earlier.

The question of toxins is an interesting one to consider, I have never observed anything that suggested to me that it hurt the crops around it, but if there are substances that damage the soil ecosystem, or can be absorbed by the crops and then us, that would give me pause. Any other alternatives beyond just straw or hay? In my experience, I haven't found these to be nearly as effective at suppressing weeds (and indeed can contain plenty of weed seeds themselves), and we are always scrounging for every last bit of carbonaceous mulching material we can scrounge up for the trees, garden, and composting toilet as it is, certainly not enough to cover everything in a thick enough layer of mulch to suppress weeds, especially perennials. Meanwhile cardboard and newspaper can be diverted from the waste stream into a free, effective resource and tool. Definitely a lot of gross chemicals involved in paper products, I would be interested to learn more how much of a concern they truly are in a garden.

It seems like the perfect tool though...trash used in a variety of handy ways. However, the issues with paper/cardboard items and chemicals are real and complicated. This link should be enough of a starting point to go down the rabbit hole:

https://www.paperonweb.com/chemical.htm

So it isn't simply glues and absolutely not just wood pulp. The FDA in the US addressed 3 chems in wide use for things like pizza boxes. That only scratches the surface. Look on the bottom of a LOT of produce boxes. Many contain warnings regarding reuse. I agree with someone way back on this thread that cardboard shouldn't need these things.

We all make our own decisions of acceptability but I'm expending far too much effort and time to build long-term resources here to not consider the precautionary principle. I don't use paper in the compost. Usually what does come onto property as a result of shipping and/or transport leaves just as quickly. Almost anything could be used for something else or in new ways. I guess I'm trying to say I try not to let "can be doing" override "should be doing". I'm already dealing with decades of coal burning and don't feel like I need to be trading current legacy issues for future potential ones. YMMV.

The mechanical pulps are primarily used in newspaper and magazine paper and the chemimechanical pulps for cardboard and soft paper.

--wikipedia

I was trying to find a way to determine which kind of processing from the feel 9f the cardboard, but it doesn't seem likely.  And there have been multiple mentions of newspaper causing problems on this thread.  Hm.