The Great Mulch Experiment
- Judith Paul
- Sep 30
- 5 min read
Updated: 2 days ago
From waste to worm food.
Someone once told me that bare soil is like a wound in the earth. It’s unnatural for soil to be exposed, so nature fills the gap, starting with weeds that grow from existing roots or from seeds carried by the wind. These weeds act like a scab, stopping soil from washing or blowing away and providing ground cover for insects, reptiles, and small mammals. From small beginnings, larger plants can grow, up to and eventually including the regeneration of forests.
With this in mind, it has been my practice for decades to mulch my gardens with pine bark because it benefits the soil, retains moisture, prevents weeds, and is aesthetically pleasing.
The problem with mulch is that it needs to be acquired and then applied. At 22yo, that was a big job but manageable. At 62yo, it’s a behemoth of a task that I absolutely loathe, and it’s not cheap! Over the years, I have spent thousands and thousands of dollars purchasing mulch, and then, to add insult to injury, damn near killing myself spreading it!
Over the last several years, I have been thinking a lot about alternatives to traditional mulching. I wanted a product that was cheap, lightweight, and readily available. As I was packing plants one day, I looked at the shredded cardboard I had recently started using to fill the voids in the boxes, and a light bulb went on. I had plenty of shredded cardboard – far more than I needed – and it was starting to become a nuisance. Remembering an article I had read about worm farmers using ripped-up paper waste and cardboard in their vermicomposters (i.e. worm bins), I wondered what would happen if I spread the excess shredded cardboard on my gardens.
In the past, I have used sheets of cardboard and newspaper, which worked well as a weed barrier, but it could be time-consuming to apply and definitely wasn’t a job for a windy day! Cardboard boxes often needed to be ripped apart (or cut with an old pruning saw) to fit around plants. Occasionally, those pieces would slide out of place and cover small plants or end up one on top of the other several feet away from where I had put them, along with the mulch on top of it. It was also doing the job twice – once for the cardboard and again with the mulch ‘topping’.
With two 5-gallon buckets of shredded cardboard in each hand, I headed for the gardens and spread them in an area that I could easily keep an eye on. My main concern was that the small pieces of cardboard would blow all over the place. It didn’t. I was worried it would block rain from reaching the soil, but it actually performed better than mulch or whole cardboard sheets; with the soil underneath the shreds damper than areas covered by aged pine bark mulch. It looked a bit unusual, with colored cardboard creating a confetti-like effect compared to the plain brown cardboard, but a sprinkle of plain brown shreds soon fixed that. I also wondered whether the shreds would ‘melt’ into the soil quicker than wood mulch, but six months later, the original area still has a covering of shredded cardboard, and although obviously composting into the soil, it is still noticeably there!
Am I worried about the ink, wax coating, sellotape, staples, and the plastics from shipping pouches going in the garden? To be honest, I was a bit concerned, but the worms are telling me they aren’t at all bothered by it. They’re loving the shredded cardboard, and it’s worm genocide if I need to turn over the soil in those areas.
Do I care about eating produce from the areas with shredded cardboard? Nope, not at all. By the time it’s composted and then processed by the plants, any undesirable trace elements (if they do exist) are likely to be so minimal that they would be insignificant. Walking on the footpath of a busy road would probably expose me to more contaminants than eating an apple from a tree that had shredded cardboard put at its base the year before.
What are the downsides of using shredded cardboard? So far, none. Some people may say that 4 x 5-gallon buckets at a time is too slow, but it suits me just fine because I don’t have the time to do all the gardens at once, nor do I need to because I don’t have a truckload of mulch sitting in the driveway. The pressure is off! Instead, I work on an area of the gardens in between other chores and whenever some spare shreds are available. It takes maybe 30 minutes to weed an area and spread the shreds from 4 x 5-gallon buckets. I can find that in my schedule more easily than a week of hard slog to weed all of the gardens, and then spend another week spreading wood mulch (oh, my aching back!)
Isn’t shredding cardboard a tedious job? Not really. I don’t do it for hours at a time. It only takes a few moments to split up a cardboard box that some cereal came in and put it through the shredder. Ditto for junk mail, Amazon and Chewy boxes, as well as all the other packaging that becomes ‘waste’ during the day. When shipments of plants arrive, it can take a bit longer to process all the cardboard boxes and packaging, but time to set up new arrivals has already been scheduled, and another 30-60 minutes for cardboard clean-up is now included.
There is an endless supply of cardboard and paper. On rare occasions, I run out of ‘waste’ to shred. Putting the word out to neighbors or picking up some unwanted boxes at a box store soon replenishes my supplies.
In Conclusion
My criteria for a mulch substitute were:
Lightweight
Cheap and readily available
Easy to apply
Fit well with my schedule
Eco-friendly
Were the objectives met?
Definitely lightweight. I can carry 4 x 5-gallon buckets of shredded cardboard effortlessly, and I could make multiple trips without any physical difficulties.
Zero cost. Other than a very reasonable and affordable investment in the mulcher (aka ‘The Mighty Muncher’), there is no cost in acquiring the raw material, and there is an endless supply of it.
Shredded cardboard is so easy to apply that it’s ridiculous. All I do is shake it out of the buckets and spread it around with my foot – no bending or shoveling!
Gone are the days of scheduling weeks of back-breaking labor or hiring helpers. When four buckets are ready to go and I have half an hour spare, another section of the garden gets attended to.
Despite initial concerns, the soil seems to be in better condition since I started using shredded cardboard, and I feel good about repurposing a waste material that would otherwise go out in the recycling bin. Water consumption has also been reduced.
Article by
Judith Paul
Hi, I'm Judith Paul, with a gardening style best described as “Oooo, there’s a gap over here!” My work history is equally unpredictable (possibly even quirky) and ranges from pulling eel-infested cow carcasses out of creeks to managing multi-million-dollar projects across various industries. I’m a Kiwi (referring to the iconic flightless bird of NZ, not the fruit) who has also lived in Australia. Currently, I run a licensed and inspected plant propagation nursery in North Carolina (USA) when I’m not teaching, writing, or editing.
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