Cardboard Composting Increases Soil Quality

There is something fascinating about the process of taking all these materials, combining them together and turning them into useable soil, in particular when you can make use of a common item that would otherwise clog our waste stream. Learn how sorting the “garbage in” results in “garbage out” that improves the quality of your gardening soil. Let’s talk cardboard composting. But first . . .

What is Composting?

Composting is an easy way to turn waste into useful soil. Basically you add brown stuff to green stuff with water, air, time and heat and eventually you get compost — dirt that can be rich in nutrients that plants need to grow. Materials that you might otherwise throw away include dead leaves, straw and wood chips, shavings or sawdust (sawdust from wood not chemically treated) along with grass clippings (grass not treated with an insecticide, weedkiller and/or non-organic fertilizer), vegetable scraps, coffee grounds and tea bags. If you are interested in starting to compost, check out our blog post Why Composting is Important and our LivingOnThePatio Starter Kit includes a worksheet for instructions on building an outdoor compost pile (heap). Get it here.

Why Do People Compost?

People begin to compost for various reasons: 

• A city or county may require a reduction in the garbage or trash taken to a landfill. Banning organic waste (leaves, straw, vegetable scraps, etc) reduces that amount by one-third according to the Frontier Group. 
• As more concern grows about global warming, some seek to use composting to reduce their carbon footprint.  
• Others worry about the use of synthetic chemical fertilizers which can deplete the soil in the long run.  
• Most often compost becomes important to the person becoming a gardener or a plant parent as compost can be used as mulch for gardens, fertilizer for potted plants, and as a soil conditioner.  

What Makes Good Compost?

If you, as I am, are looking to use compost to grow vegetables and herbs as well as the blooms in your garden, you will want to make sure that you use certain trash materials that will help your plants thrive. For example, for years I would happily accept any and all of our friends and neighbors’ grass clippings and dried leaves to add to my compost pile — that is, until I learned that one lawn was habitually sprayed with an insecticide, weedkiller and fertilizer. Yikes! This was not what I had in mind for my garden. As I began to pay attention to the source and care of the materials put in my compost, there were some things I learned along the way.

Be Choosy About the “Garbage In”

Know what leaves to compost.

Some leaves compost more effectively than others and the best are those lower in lignin (the chief substance in wood) and higher in calcium and nitrogen. These include maple, elm, ash, birch, cottonwood, poplar, cherry, and other fruit tree leaves which will typically break down in about a year. Avoid the leaves of the black walnut, horse chestnut, beech, oak and holly according to Simple Garden Life. 

Know what paper to compost.

Most of the time, it is recommended that you use untreated paper for your compost. Newspapers work, despite the ink, as do some types of already recycled paper. What about paper with computer, pen, or marker ink or dyes on it? If the ink used is vegetable-based, soy-based, or non-toxic, then it’s safe for the compost according to Green Matters.

Know what tea bags to compost.

The paper used in high quality tea bags is fully compostable. The vast majority of brands on the shelves have mesh tea bags that are composed of 20-30% plastic which will release microplastics and nanoplastics. The string used in standard tea bags is fully compostable. The staple that secures the paper tag to the string is not. The adhesive used to heat-seal the edge of the paper tea bag is not compostable according to Recycle A Cup.

Know what cardboard to compost.

Uncoated boxes (not shiny) with no heavy dyes. Unfortunately, that shiny cardboard is coated with plastic that cannot be composted. Remove all the tape or labels as these are not compostable, either. Shred or tear the cardboard into smaller pieces according to packmojo.com (more on this later).

Ways to Use Cardboard in the Garden

So now what? After learning which materials to be choosy about, it became obvious I was going to have to find another source of “browns”. As you recall from our previous post, browns are the materials high in carbon and low in nitrogen (the opposite of the “greens” which are high in nitrogen and low in carbon). I live in an area where most of the trees are oak and walnut. However, like most, I had an excessive amount of cardboard boxes, and happily turned my attention to cardboard composting.

There are many ways cardboard boxes can be used in your garden as cardboard composting:

1. Small cardboard boxes can be great to start seedlings and protect plants from weeds when the whole box is set in the ground. 
2. Larger boxes can be the base layer in the sheet composting method or the “lasagna method” of compost (uses a layer of cardboard or newspaper positioned in the yard adding soil with mulch on top; the cardboard helps to smother existing weeds and seeds). This method is mostly useful in building up garden beds, especially as it takes longer for the cardboard to break down.

But if your household is like mine, every online purchase brings a box that is a great candidate to become a “brown” in your compost pile. It’s best if the cardboard box can be reduced to smaller pieces. The thing is, have you ever tried to cut, tear or shred a cardboard box by hand? After a while, it’s difficult — my hands hurt either using scissors or trying to tear along the folds, and soaking the boxes in water (a recommendation from packmojo.com) was too messy for me. 

Is Shredding Cardboard Feasible?

Thus began a search for an affordable way to shred cardboard. For all the increase in online purchases as well as the chatter about keeping cardboard out of landfills, it was not an easy task. Cardboard is NOT just lots of paper stuck together. Waste corrugated cardboard is mainly composed of 52% cellulose, 7% hemicellulose, and 11% lignin – think tree trunk material. We tried using a chipper-shredder from a national retailer, thinking that if it could grind up sticks and branches, cardboard should be no problem. It jammed on the first run.  There was a high-end shredder designed for cardboard but it was $700, really for warehouses or distribution centers that apparently reduce lots of boxes daily. So I intensified my online research to find something cheaper; useful for a household but able to shred the cardboard for my cardboard composting pile. We selected the Bonsaii 3S30 and it works great! It’s available at Amazon.com. Look at the lovely shreds destined for the compost heap!

Keep That Shredder Running

The Bonsaii 3S30 does a great job shredding your cardboard boxes, but it needs some maintenance to keep it running in good shape. First, remember to remove all the labels, tape, and staples from your boxes. You will need to cut the cardboard box to a piece the size of the hole at the top of the shredder feed. After you have filled the shredder basket twice, use the Bonsaii Shredder Lubricant Sheet (also available at Amazon.com) to keep the blades well-oiled. Because the shredder produces dust, we make sure to use an air purifier in the same vicinity – we use a MOOKA Air Purifier, available at Amazon.com.

Remember the Other Composting “Don’ts”

• Don’t add fish, meat, dairy products, bones, baked goods, fatty foods or grease to your compost pile. These food scraps do not easily decompose and may attract unwanted animals.
• Don’t use diseased plants or plants that are toxic to other plants. Also, avoid weeds, which produce abundant seeds, because they may not be killed during the composting process.
• Don’t add pet feces or used kitty litter. Although they may eventually break down in compost, they also harbor bacteria, germs, viruses and parasites.
• Don’t use sawdust from treated wood, coal fire ash or synthetic fertilizer, because they can harm your soil and plant health. 
• Don’t add glossy or coated paper. Also, avoid composting sticky labels on fruits and vegetables, because they are not biodegradable. 

Cardboard Composting FAQs

 Is cardboard good for compost?

Yes, you can compost cardboard. In fact, cardboard waste makes up over 31 percent of landfills according to the United States Environmental Protection Agency. Cardboard composting is a practice that is becoming more popular now that people are beginning to realize the benefits of composting.

How long does it take for cardboard to decompose in compost?

If you do nothing to your large pieces of cardboard, then it can take them naturally about six to eight months to break down completely. Obviously, if you shred your cardboard it will decompose quicker.

Does cardboard need to be shredded for compost?

Cardboard is very good for improving the structure of compost because it helps introduce air pockets. Oxygen is an important ingredient because the composting microbes need it to do their job. In my experience cardboard needs shredding. If it’s not shredded, large sheets will stick together in a big damp mass.

Check It Out

Check out our blog post Why Composting is Important and Our LivingOnThePatio Starter Kit includes a worksheet for instructions on building an outdoor compost pile (heap). Get it here. And remember, every day is Friday on the patio! Kick back with an adult beverage and a snack and watch your garden grow with your own rich compost.

Please Leave a Comment: Cardboard Composting

Leave a comment below and tell us if this information was of value to you or let us know what we missed and can add to this post. Do you compost? Do you practice cardboard composting? If so, how is it working? Do you shred your cardboard? Please post a photo of your compost heap — we’d love to see your garbage!

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