👋🏼Hi there.
You may have seen 2xEDGE photos and video showing how we use cardboard to smother grass and weeds and create garden beds and paths.
I've used this method many times and a quick search online will likely reveal a lot of other DIYers and gardeners doing the same.
Well, guess what?
That cardboard we're all putting on - and ultimately into - the ground to make quick work of garden bed prep while feeling great about adding carbon to the soil and feeding earthworms with that delicious rotting layer of cardboard?
WRONG.
In prep to write this post I did a bit of research on the topic of cardboard uses in the garden. That led me to change the working title from "How To Make Quick Work of Garden Bed Prep with Cardboard" to the title you see above today.
Mea culpa! Apologies! I can explain!
First, some level setting.
What Is the Cardboard Method?
If you don't know about the cardboard method (sheet mulching with cardboard) here's what's what:
You want to create a new bed - vegetable garden, flower bed - in your garden. Or maybe you have an area in your yard where you envision a glorious new planting area covered with gorgeous organic matter and ready to offer good things from your compost pile to the roots of your plants. Heavenly vision!
Thing is, the area where you'd like to add this new garden bed isn't bare soil. It's covered in grass and/or weeds.
Hmmmmm.
You've heard about layering regular cardboard boxes on the ground and then adding a few inches of dirt and/or mulch over the top of the cardboard. (You've maybe also heard you can use layers of newspapers or brown paper…. Keep reading....)
These layers block all light from getting to the grass and weeds below, killing them off completely and making the area ready for your curated plantings.
You turn to the internet as we DIYers do 🤓 and find evidence all over the place from cardboard proponents that using cardboard in this way is a great solution for getting this job done with no negative effects.
Got a big area with a weed problem? No worries! It's just pieces of cardboard.
And it's so easy!🎉
No digging up grass or pulling weeds. The only tools you'll need are a box cutter and a garden hose. Bonus: you'll get excellent results since the cardboard will positively add to the soil structure as it breaks down.
So you collect plain cardboard boxes - no waxy or glossy finish, minimum to no ink - and feel great about returning cardboard - which is made from trees after all - to nature rather than using landscape fabric or sheets of plastic.
So you put down layers of cardboard in your designated area, soak them with water, then add a layer of dirt, and finally a layer of mulch.
And your new bed is ready for planting in the next growing season.
Done!👍🏼🙌🏼
Is The Cardboard Method Bad?
I have been here and I have done this.
I have felt great about the bed I've created.
I have put native plants into my new bed and marveled at all of the cardboard-to-carbon nutrients that must be available to my new plants.
Only thing is: uh uh. 😑
And: uh oh. 😐
Enter The Garden Professors
The Garden Professors (I'll call them The Profs from here on out) have been "advancing the science of gardening and other stuff since 2009".
Other than conceding one exception regarding using newspaper layers to sheet mulch vegetable gardens (see "Sheet mulching - benefit or barrier?"), The Profs are clear in their rebuttal of the cardboard method:
Don't do it!🚫
They're also clear in their suggestions for an ecologically positive way to handle the task of eradicating grass and weeds for new planting areas: Use wood chips.
Let's get into it.
The Cons of Using the Cardboard Method
(Per The Profs, there are no pros.)
Nurturing Isn't In Cardboard's Nature
In August 2015, The Profs published "The Cardboard Controversy". In it, they detail many of the problems that using cardboard in our gardens can create.
Cardboard boxes are meant to protect the items that are put into them and so are made from a material that is tough.
That tough protective layer aims to keep out moisture and gases and this, The Profs argue, makes cardboard unsuitable for nurturing soil life (bugs, worms, microbes - aka the wild things that are the best friends of the garden!).
Covering soil with cardboard decreases the gas exchange between the soil and the atmosphere. This has a negative effect on soil biology and the habitats of soil organisms.
Save the soil! Skip the cardboard!
We ❤️ Earthworms! Cardboard Doesn't.
I hated reading this in "The Cardboard Controversy":
"We've all observed that earthworms crawl to the soil surface during heavy rains; this is due in part to water filling their burrows and reducing oxygen availability…. Likewise, the reduction in oxygen movement from the atmosphere into cardboard-covered soil would cause worms to crawl upwards in an effort to find oxygen at the soil surface."
In other words, when we use the cardboard method we risk suffocating earthworms!🪱
Save the worms! Don't use cardboard sheet mulching!
Termites ❤️ Cardboard! Need I Say More?
In "Why I don't like cardboard mulch" The Profs" write:
"But there's one area where cardboard is tops compared to every other mulch material tested."
"Termites."
So skip the cardboard and skip inviting hungry termites to visit your property.
Diamonds 💎 Are Forever. And So Are Chemicals in Cardboard.😖
Even though we work hard to use clean brown cardboard to create garden beds, The Profs write that cardboard may contain chemical contaminants such as per- and polyfluoroalkyl substances or PFAS.
From the US Environmental Protection Administration's "PFAS Explained":
"Because of their widespread use and their persistence in the environment, many PFAS are found in the blood of people and animals all over the world and are present at low levels in a variety of food products and in the environment."
Repurposing cardboard for weed control and/or grass removal introduces these contaminants into the soil environment.
Howsabout: no!
Research, Research - Where Is the Research?
In March 2024, The Profs published "Cardboard does not belong on your soil. Period."
In this Q&A-style post, written nine years after "The Cardboard Controversy", the Profs argue that (not counting their 2019 peer-reviewed study) there continues to be a lack of research into the effects on people, critters above and below ground, and the environment when we use cardboard as organic material in our gardens.
In other words, we don't know what we don't know, or what we do know.
Proceed with caution.⚠️
And consider erring on the side of not suffocating earthworms or adding harmful chemicals into your vegetable beds!
So, Now What?
It Always Comes Back To Wood Chips, Doesn't It?
According to The Profs, the best way to kill off grass and weeds in prep to create a planting area is to dump a lot of wood chips directly onto the area where you want to start growing things.
To be clear, they suggest you dump 12-inches of wood chips. Yes: a foot of mulch! They say it will compact down to about 8-inches of mulch relatively quickly. Over a year it will likely compact down another 4-inches.
Depending on the size of the new areas you are creating, a foot of mulch might feel like an overwhelming amount both in terms of, well, amount and cost.
The good news is, you can get wood chips for free!
Check out our post, "Bagged vs Bulk Mulch vs FREE: Which is Best and Why?", which details a number of ways to get free wood chips - delivered even!
About Wood Chips & Nitrogen
Like me, you may have heard that you shouldn't use wood chips around your garden plants or trees until it's been aged because it will steal nitrogen as it seasons.
According to The Profs, this is not the case. See "Wonderful Wood Chips" where this is discussed in the comment thread.
Save A Step Or Three
Skipping the cardboard layer and going straight to wood chips saves you some steps:
- Collecting cardboard boxes.
- Cleaning up the cardboard boxes - removing tape, labels, staples.
- Breaking apart and spreading out the cardboard in overlapping layers.
I guess we can add a fourth step - the need for termite eradication. See above.
So, Now You Know
Who knew, right?
Well, clearly The Garden Professors knew. And now we do.
I hope that this post has been helpful to you. If it has and you're all in on wood chips and only wood chips to create your next gardening area check out "Bagged vs Bulk Mulch vs FREE: Which is Best and Why?". It includes more than a few tips on obtaining this magical mulch!
And on the topic of new gardening areas, we've got a fast and easy way for you to add borders to all that new gardening space. Check out 2xEDGE Staples and transform common two-by (2x) lumber into landscape edging and garden borders with just a rubber mallet. No digging or drilling.
Thanks for reading!
Photo Credit
Thanks toMarkus Spiske on Unsplash.