Corrugated cardboard - is it ok for mulching?

I recently had a great question from a new organic allotmenteer called Doug, who said some very lovely things about my book, and then asked:

"You suggested the use of cardboard for weed suppressing/mulching - I have access to loads of it! But is it known if the adhesives used in the cardboard industry to stick the layers together break down to harmless elements? (Sorry if this seems overzealous). "

On the contrary, Doug, this is a darn good question and one I have occasionally pondered, so your email offered a great big kick up the backside to search out the answer before I use any more cardboard on my allotment, in pursuance of my mission to mulch, mulch, mulch this year. I should clarify at this point that what Doug was worried about was corrugated cardboard - the stuff with a wavy sheet of cardboard stuck between two flat sheets, and frequently used for boxes.

An initial, cursory Google search revealed very little of help, so I turned to the UK authority on all things organic - Garden Organic, formerly known as the HDRA. One of the benefits of being a member is free advice on such tricky matters, and a few days after submitting my query I got this response from Garden Organic adviser Carrie Pailthorpe:

"The type of cardboard you describe does not usually contain glue as it is made from cellulose fibres which stick together naturally. It is a great addition to your compost heap or can be used for mulching."

Well that is good news! I'd still advise removing sticky labels, tape and staples from your cardboard before use though.

In other exciting compost news: I have found a source of both straw for mulching and well rotted manure! A lovely lady called Laura swapped me bags of straw for some of my blackcurrant jam. I shall be popping back to her stables for some manure when I don't have the baby in tow ...

Comments

[James Heywood]

Thanks for mentioning cardboard in your book. At last, something I can use that doesn't cost me money! I'm forever on the lookout for boxes now. It's funny how allotments change your perspective on the world isn't it?

[Jane Perrone]

Thanks James! Will add a link to your blog from my allotmenteers blogroll. YOu have my sympathies over the waterlogging ...

[Natalie El-Barrawi]

Top tip:for free cardboard of the big kind-keep on the lookout behind fridge and cooker shops as they have almost bed sized boxes flat-packed and ready for the dustmen to collect.
I visit just before bin day and stash them on the lotty for future use.

[ricki]

There is a long fence line (wire) between our place and the neighbors. It gets a lot of sun, so the first year I planted tomatoes there, and cucumbers meant to climb the fence...complete bust. I then learned that Jim was in the habit of spraying Roundup along the fence (he likes things tidy). Once he (a very nice man) saw what I was attempting, he stopped spraying and weeds jumped in gleefully. Last fall, I put cardboard under the fence and covered it with cedar shavings...looks nice and my fingers are crossed, hoping for less work in the weeding department.

[Gordo]

I stumbed accross your article when I too was searching to find out about corrugated cardboard for mulching. I used it last year with GREAT SUCCESS but wasn't 100% sure if it was OK (even though I originally got the idea from an organic gardening show). I did more research - your quote says corrugated cardboard does not usually contain glue - we'll maybe its just a slight technicality - but what I found was that the corrugated cardboard manufacturers use "cornstarch glue" - however this is all natural and biodegradable, it comes from corn, they get it in powder form, and add water. More can be found in a google on "corrugated cardboard" "biodegradable" or "how corrugated cardboard is made". The good news is that it is completely biodegradable, and it works great for weed control, I will keep using it. Even the inks they are using for printing on the cardboard now are all natural, soy based and wax. The pulp used it usually pine.

[gregg thefarmguy]

i have used cardboard between our raised beds for weed supression and under the pumpkin and squash, wanted to find out if i was creating toxins in the soil, found your site on a google search, thanks for the information. yes those appliance boxs are great!

[Rachelle Ackerman]

Thanks for this info. I will now happily use corrugated cardboard without worries. However, I have another question for you: what about tag-board (like cereal boxes) type cardboard? I just came into these great, large sheets of it, unbleached and no tape, inks etc. and I'm wondering if it's just as benign as the corrugated kind? Thanks to whoever knows the answer!

[Emily]

Please help! My community garden just banned the use of corrugated cardboard in garden plots, claiming that it contains formaldehyde! I used corrugated cardboard boxes to begin my no-dig raised bed garden, so I am trying to find the truth to this claim (I have asked them and they have given me no links yet). I have searched the internet through and through and have found no information that says that corrugated cardboard contains formaldehyde (I have found information that paperboard and boxboard, which cereal boxes and such are made of, does contain it.) Ok, so my issue is this: the person who sent this email gave no reference to the source of the claim, no discussion as to the validity of the claim, no nothing, but all I can find is support and praise for cardboard in the garden (that's how I happened upon this site)! I am a Board Member of my community garden (a non-profit organization) and am also an organic gardener and grower (I started a mini-nursery along with a large garden operation this year for farmer's markets and such as a profession). So this is of particular interest to me, since the claim came from no-where (they discussed it at the board meeting last night apparently, but I missed it because I had a farmer's market to attend)... with no reference or links or any proof, and I have been searching all day for the proof but cannot find it (so am I just not "In the Know" or are they ignorant to the different types of cardboard?)... Any help?!

-Emily

[Jane Perrone]

Emily, I don't know the answer but will ask around and see what I can find out. Sounds as if they might be mixing up cereal boxes with corrugated cardboard ...

[Colin Hallahan]

I have been wondering the same thing. Some other info I've gathered suggests that the layers are glued, but with a starch based glue that should bio degrade.
http://en.wikipedia.org/wiki/Corrugated_cardboard

Some other thoughts:

Wooden shipping pallets from overseas (I'm in the US) I'm told are sprayed with an insecticide. Naturally, since so much global shipping is going on, one might wonder about the boxes on the pallets as well possibly having some spray on them.

Finally, many folks want to use free/recycled items, such as those shipping pallets for projects, including top bar bee hives and the like. Might we worthwhile to try to identify where one's recycle is coming from to avoid unknown chemicals.

[Eduardo]

We've only got a few cardboard boxes here, but some people want to throw them away... After Googling for info on cardboard and mulching, I found this page... Thanks for all the info... hopefully this is all the proof I need. ^^

[Dusty Williams]

I'm an opererator of a recycle depot in a small town on the edge of the Rockies. Since the crash of the recycle market a couple of months ago, we have been stockpiling our corrugated cardboard, which is growing at a rate of half a metric ton a day. We were thinking of shredding the product and using it for mulch on our parks gardens and such, as well as making it available to the public. My next question is; can the coloured corrugated cardboard be used? The shiny surface is usually a clay base with water or food based inks. Are you aware of this product being used, or of any health, or contamination concerns? Sure would be nice to at least utilize the plain brown cardboard for a start.