Creative ideas on turning cardboard into dirt/mulch?

April 12, 2022 11:18 AM

I have a lot of cardboard. I live in the middle of the woods and many things are shipped to me. I have a gigantic pile of non-glossy cardboard that I would like to turn into dirt or mulch (which will eventually be dirt). None of my attempts have worked very well.

Things I have tried already:

I purchased a used Echo Bearcat SC3206 used from facebook marketplace. After getting the blades sharpened, it works pretty good on branches, but not so good on cardboard. The leaf shredder functionality doesn't handle the cardboard well, and the wood chipper chute is very difficult to jam the cardboard into. The best experience I had was carefully rolling the cardboard into a branch-shaped-cardboard-log and shoving that into the chipper. It was very slow.

I have used cardboard as sheet mulch in some places, and then covered it with rotten hay or straw. This works pretty good, but it is very work intensive and requires some other kind of mulch-topper or the cardboard will blow away. I tried using lawn staples to hold the cardboard in place, and while this does work, it is still really work intensive and also extremely ugly.

I don't have a tractor, so I do not have access to PTO solutions. Though that would be really nice, honestly. At this point though, I have nowhere to house a tractor.

What I want is some solution where I can buy or rent some machine that will turn this gigantic pile of boxes into a medium-to-large pile of shredded cardboard that I can use as mulching. I don't have infinite money, I think I could get $700 for the bearcat if I wanted to trade up to something else. Rental would be ideal. Or someone I could hire, but I don't even know how to describe what I want or what business would have a tool to do this.

posted by pol to Home & Garden (29 answers total)

Because shredded cardboard is just shredded paper, it will be blown away unless contained.

Give you want mulch, I guess wetting down the corrugated cardboard a little is not viable, huh? That would make the cardboard bit more pliable and thus a bit easier for the shredder. Don't need a lot.
posted by kschang at 11:28 AM on April 12, 2022

I wonder if any landscaping companies near you would have an idea of whether their bigger chipper-shredders would work? Might be worth a phone call. Seems like the kind of thing you could hire someone to come do for a few hours for a similar price as an equipment rental.

Another idea: stack it up, weigh down the edges and cut with a chainsaw. Then take the smaller pieces, put them in a big garbage bin and shred further with a weed whacker. (Put the weed whacker in the bin as if it's the mixing paddle and the bin is the mixing bowl.) Please wear plenty of protective gear!
posted by purple_bird at 11:30 AM on April 12, 2022

Best answer: Wet it down and turn it into mush. You can experiment with a 5 gallon bucket and a paint mixing bit on a drill. Use lots of water to start and see how much cardboard you can mix in. Do you want it to be clean? Then pour it over a screen. If it doesn't matter, just pour it over some dirt and the water will drain away. Mix as it dries and you basically have cardboard compost.
posted by soelo at 11:35 AM on April 12, 2022 [3 favorites]

Best answer: If you are in the woods, how about just a big pile of compost? I don't do this with cardboard, but I basically take all of my yard and lawn materials and (green and brown) and throw it into a big pile in the woods and add to it all season. Then the next season I start a new pile. I'm on a three-year cycle now as it takes about 3-4 seasons for a pile to become compost as I am not using best composting practices (like turning and aerating) but it's maintenance free other than throwing onto the pile and I just let nature and time do it's thing. You need some space for this and enough "green" to add to the cardboard to make it actually become compost, but I tend to throw all of my grass clippings and kitchen veggie scraps into it.
posted by archimago at 11:37 AM on April 12, 2022

Response by poster: Ooh, I did not think of getting it wet and turning it into mulch-paste! I shall try that. This is a good idea. Should I use a kiddie pool or stock tank for the cauldron? OR should I just use the ground? I feel like it would need to soak.

My only concern with "forest piles of cardboard" is that the woods aren't extremely close to where I want to use the cardboard, and it sounds ugly. Hm. Maybe I could find a way to make a tidy "mulch reactor" (something to contain the cardboard pile). I could maybe come up with a chicken wire cylinder or something similar to keep it from being a sprawling mess. This is also a good idea and I will experiment with it.

To clarify, it is totally fine if this takes a year or three to start making mulch or dirt. I just want a workflow.
posted by pol at 11:48 AM on April 12, 2022

This won't help with your current pile, but for future deliveries: I have a 12-sheet paper shredder that handles the average cardboard shipping box with ease; I shred each box shortly after it arrives at my house so I don't accumulate a backlog and then enjoy a steady supply of shredded cardboard to mulch plants with or add to my kitchen waste compost tumblers.
posted by Tuba Toothpaste at 12:24 PM on April 12, 2022 [1 favorite]

I shred cardboard and put it on my compost pile and in general, it doesn't fly away. Especially after it gets some rain on it. I just throw it on top and consider it a "brown" in the compost lasagna ingredient list.

My paper shredder says it handles up to 12 sheets of paper but I hear it working hard on that much so I usually try to do about half. Cardboard/cardstock sheets go in fine but for corrugated cardboard, I usually peel it apart and put each half in separately. If you have a huge mound, a better shredder will probably be what you want but I don't think it needs to be a crazy expensive industrial one or anything like that.
posted by dawkins_7 at 12:25 PM on April 12, 2022 [1 favorite]

Response by poster: Shredding people! Can you let me know what specific equipment you are using to shred cardboard successfully?
posted by pol at 12:40 PM on April 12, 2022

Response by poster: My only fear with non-commercial paper shredders is that my volume will destroy it and I will have created an additional waste problem for myself (and e-waste is by far my least favorite problem to deal with waste-wise).

I did find some commercial ones that look great, but I have no idea where I would put it (nor do I think it makes sense to house something of that magnitude). I might be able to convince my town to buy one though if it is less than $5k and we could use it to make municipal cardboard mulch for all.
posted by pol at 1:09 PM on April 12, 2022

Something you could try is using a box cutter to slice a few of your cardboard bits into pieces maybe half the width of your lawn mower's cutting circle, then running the mower back and forth over a pile of those to see what happens. I've found that my own lawn mower makes a much faster job of reducing piles of sticks and small branches to mulch than any machine that wants them hand-fed, and it seems to me that if you cut your cardboard just small enough to get its edges sucked up into the whirling blades of death without being held down by the wheels, you might well find that the same applies to that.

Might also be interesting to see what happens if you run a lawn mower over a pile of cardboard that's just been hosed down enough to get properly floppy.
posted by flabdablet at 2:12 PM on April 12, 2022

Yet another thing you could try is making some fairly tall raised garden beds, then using cardboard sheets as-is to fill most of their volume, with maybe nine inches of topsoil over the top. Over the course of several years the cardboard would really have no option but to break down and become incorporated into the soil as humus. As a high-carbon, low-nitrogen material it would undoubtedly bind up nitrates from anything it was immediately in contact with as it broke down, so you'd probably want to include a layer of a fairly hot manure (chicken would be ideal) every few layers of cardboard.

You could even bang in some fairly closely spaced wooden stakes or star pickets, then use multiple thicknesses of cardboard sheet supported by those to build the walls around the raised beds. They'd get soggy and bulge a lot after the first rain or thorough watering, but since they'll be rotting from the inside out they should last at least a couple of growing seasons, after which you could re-use the now completely tattered outsides as the innermost or undermost layers in another raised bed, leaving the remnants of the old bed as a simple mound garden.

Earthworms will certainly appreciate all the corrugated cardboard's pre-fabricated earthworm habitat once it's been nicely dampened under soil. Plus, you could keep an eye out in your garden beds for signs of termite activity, possibly getting warned early about possible forays into any wooden buildings on your place.
posted by flabdablet at 2:37 PM on April 12, 2022 [1 favorite]

Best answer: If you can find sets of four or five boxes that nest reasonably well without even being flattened, you could fill the innermost one with topsoil and use them as container gardens for herbs, strawberries, cherry tomatoes, chillies and whatnot.

I'd expect that by the time they got rotten and pulpy enough to tear and leak soil, you could shovel the whole container straight into a compost heap, soil and all, to finish breaking down.
posted by flabdablet at 2:54 PM on April 12, 2022 [3 favorites]

Response by poster: Yeah, I have had some good success integrating cardboard into my various soil building and mulching projects, I am just dissatisfied with the amount of work to use it as a general purpose mulch medium. I have a keyhole bed that I grew potatoes in last year (and will again this year) that is composted almost entirely of yard waste and cardboard. It's my go-to location for dumping cardboard now and again, but it takes a lot of work to tear up the cardboard (otherwise it takes SO LONG to decompose).

One of the machines that came up during some thread research was the commercial machines that turn cardboard into packing material. I didn't know that these existed, but they would probably do what I need. I would bet that the processed cardboard would probably not blow around if they were hit with a bit of water, and would decompose a bit better than leaves. But these are so expensive, and they want a commercial space not a cluttered garage.

I am going to try the wet-processing, forest compost pile, and if I can find the right combination of size and sturdiness, the "biodegradable pot/bed" ideas. These are some great ideas to try this year.

Even trying all three I will still have more cardboard, so any other ideas are appreciated. :)
posted by pol at 3:01 PM on April 12, 2022

Dig a long trench, bury a bunch of roughly similar sized sheets of cardboard stacked nicely, put the soil back on top, you've got something akin to hügelkultur.
posted by SaltySalticid at 3:07 PM on April 12, 2022 [5 favorites]

Best answer: It unfortunately involves buying more stuff, but I would secure a good-sized raised garden bed (something like 4m x 1m x 1m) and, using a combination of tightly-nested and completely flattened cardboard boxes (and branches and other organic detritus), fill the bed about 1/3 of the way with cardboard, absolutely soak the lot of it with water, fill the rest in with topsoil, add a fertilising compound, and plant some seasonal fruits/herbs/vegetables in it. The cardboard will be taken care of by the critters in the soil.

Cardboard as a mulch rarely works very well. It takes a LONG time to break down, looks awful, and if it's shredded it will get blown all over the place. Cardboard needs to be IN the dirt or IN the compost to be most effectively gobbled up.
posted by turbid dahlia at 3:22 PM on April 12, 2022 [2 favorites]

Our Amazon basics 24 sheet shredder handles corrugated cardboard just fine. Have to rip it into strips narrow enough to fit in a shredder, but otherwise easy. The shredded cardboard goes into the compost, where it helps get us to the right brown to green ratio and size to make hot composting achievable. The compost can be stopped early and used for mulch, if desired.
posted by deludingmyself at 3:34 PM on April 12, 2022 [1 favorite]

Another option might be to offer the boxes whole to a family who are moving houses, and ask them to try to pass them on after use too. Reusing is better than composting!
posted by nouvelle-personne at 3:54 PM on April 12, 2022 [1 favorite]

You need some greens. Cardboard is like 500:1 C:N so it breaks down very slowly. If you can find or save some coffee grounds they will help a lot. I think building a cage out of chicken wire, alternating layers of cardboard and some higher-nitrogen material, and keeping it damp will work eventually. The good news about cardboard is that it's full of air so you don't need to worry about it going anaerobic until it's quite broken down. Worms love cardboard as mentioned above so they could speed the process up but they're not necessary.
posted by goingonit at 6:36 PM on April 12, 2022

Response by poster: Hmm... yeah, if I had a tractor or something that would allow me to dig a pit or trench easily, just burying the cardboard (or making a worm pit) would be the best. But without a digging machine, it would be some serious work to bury the amount of cardboard that I have.

Even so, a cardboard-hugelkultur mound/berm would be interesting. I am just not sure I am up to effort of moving so much soil manually.

Thanks for the tip on coffee grounds, I will start collecting them separate from the other compost to use in the experimental cardboard reactor.
posted by pol at 8:35 PM on April 12, 2022

Given that corrugated cardboard has so much structure it seems a pity to waste that deliberately. You might want to experiment with taking advantage of the corrugations to use it directly as a growing medium.

I'm thinking bales of cardboard about the size of typical straw bales, tied together just like straw bales using the same polypropylene baling twine, made from sheets arranged so that when the bale is sitting flat on the ground, all the corrugations run vertically.

Now I'm thinking four of those bales laid side by side, to make a platform with about the footprint of a single mattress, and two or three inches of compost-enriched topsoil shovelled over the top to cover them.

It seems to me that the outermost parts would both retain less soil above them and tend to dry out faster than any other part of the bales, so that over time most of the cardboard breakdown would be happening in the wetter centre. It also seems to me that even well before the cardboard began to break down, plant roots would happily follow the nutrient-rich drainage from watering the bed down through the corrugations, and you'd end up with deep-rooted, happy plants.
posted by flabdablet at 3:21 AM on April 13, 2022

it takes SO LONG to decompose

You say that like you think it's a bad thing :-)

I'd encourage you to use your accumulated experience with HOW long it takes to decompose, to help you think about building stuff out of it that's deliberately designed to decompose eventually but also takes advantage of whatever structural properties it retains along the way.

Waste should be thought of as a verb, not a noun, and corrugated cardboard's cunningly engineered structure is absolutely a resource.
posted by flabdablet at 3:33 AM on April 13, 2022 [2 favorites]

Those cardboard bales could also be used as platforms to lift container gardens to a comfortable working height, then switched over to being directly soil covered once drainage from the containers had begun to rot them.
posted by flabdablet at 3:37 AM on April 13, 2022 [2 favorites]

And if the containers themselves were also made of cardboard, then by the time the rot set in and the whole works got a bit collapse-prone, you could probably just smoosh the containers and the soil they no longer retain very well over the top of what was left of the platforms using a steel rake. This would involve lifting very little soil, so it would be a fairly low-effort process.

In my world, effort is a scarce resource and wasting it counts as sin.
posted by flabdablet at 3:41 AM on April 13, 2022 [3 favorites]

Also, if I were contemplating turning a huge pile of assorted corrugated cardboard into semi-structural bales, the first thing I would do is use a bit of scrap timber to construct a baling jig to help me stack and bind sheets into bales, and a cutting jig to make slicing randomly sized boxes into sheets sized nicely for the baling jig fast and easy.
posted by flabdablet at 3:54 AM on April 13, 2022

Best answer: You can use cardboard to grow mushroom spawn and also mushrooms themselves
posted by olopua at 8:06 AM on April 13, 2022

Cardboard takes a long time to decompose because, among other things, it is extremely high in carbon. The microorganisms that decompose/make compost need nitrogen as well: the ideal C/N ratio for compost is 30:1. That means if you just put cardboard into your garden beds the microorganism breaking it down can remove nitrogen normally available to plants, in order to do their work. This can result in nitrogen deficiency in that soil.

Cardboard and newspaper have a C/N ratio of 560:1. This means to compost it/break it down properly (not just pulp it, but make it become a part of healthy soil without sucking the nitrogen out) you'll need to mix it with lots of green waste (grass clippings, vegetable scraps, coffee grounds) -about 5 times the amount in weight of vegetable trimmings to cardboard if you want it to compost efficiently.

So, to break down the cardboard without removing nitrogen from your soil: soak the cardboard until it is wet, and tear by hand in 6" or smaller pieces; or cut dry with a box cutter into 8 inch sheets and shred with a heavy duty shredder. Mix with green vegetable scraps/grass clippings/ coffee grounds at a 5:1 ratio of green to brown stuff. Pile in loose piles about 3'x3'. Keep as wet as a wrung out sponge. Stir the piles every few days. Depending on the weather it takes 2-6 months to compost cardboard in this way. Without composting it can take 6 months to a year or more.
posted by oneirodynia at 1:23 PM on April 13, 2022

Forgot to mention: some people have had success soaking cardboard for a couple weeks in a tub and then using a paint mixing attachment on a drill to shred the wet cardboard.
posted by oneirodynia at 1:26 PM on April 13, 2022

Response by poster: Upon further thought, My question was not very good, because I don't need soil.

I have two problems that I want to solve:
1. too much cardboard
2. not enough mulch (i have lots of soil/growing space)

The decomp time is a great benefit as a mulch medium, which is really what I need. I don't have enough mulch material unless I am willing to strip-mine the surrounding forest for leaf litter (which I would prefer to leave intact for the forest floor ecosystem and it's difficult).

The excellent flabdablet ideas about turning the cardboard into growing zones are, in retrospect, solving a problem I don't have. I want a mountain of slow-to-decompose mulch for weed control, moisture retention, critter ecosystem, and I just like mulching.

I think that the wet cardboard slurry would probably turn into a kind of paper mache, and this is interesting to me as it might make an interesting mulch. Or it might dry into a horrible impermeable poop emoji. It seems interesting enough to try regardless. Though _weeks_ of soaking is slow going. We will see! I also plan on trying the cardboard mulch tower (though I don't hold out as much hope for this one).

I don't have enough green compost to offset the mass of cardboard I want to process without a lot of collection effort. I would need 5x as much green as I have cardboard and I have a LOT of cardboard. While this is the "right" way to make cardboard into soil, it might not matter as much for cardboard-as-mulch. It looks like cardboard is about 20% more carbonic than wood chips, and I think that is fine, I use as much wood chips as I can find.

Oh! And I am a fungus enthusiast, I am annoyed I didn't think about cardboard as a mushroom substrate. That will totally happen, I will probably set aside the least inked of the sheets to process into shrooms. FUN.

These ideas are inspiring! Once Ramadan is over, I am going to get to it.
posted by pol at 1:37 PM on April 13, 2022

What power tools do you already have?

And could we see a photo of the existing cardboard stockpile, to get a sense of the scale of what you're dealing with?
posted by flabdablet at 11:30 PM on April 13, 2022