Why Composting Worms Love Cardboard—and How to Use It as Bedding

When people ask me what they should use for worm bedding, cardboard is almost always one of the first things I recommend. It’s inexpensive, easy to find, and works incredibly well in a composting worm bin.

Most of us have cardboard boxes sitting around from Amazon orders, deliveries, or trips to the grocery store. Instead of throwing them away, you can turn that cardboard into a comfortable home—and eventually food—for your composting worms.

At Utah Worm Company, we have used a lot of different bedding materials over the years. Some are more expensive, and some require a little more work, but plain brown cardboard continues to be one of my favorites.

Do Composting Worms Really Eat Cardboard?

Yes, composting worms will eventually consume cardboard—but there is a little more happening than simply watching a worm eat a box.

As moist cardboard begins to soften and break down, bacteria and other microorganisms grow on it. The worms feed on that decomposing material and the microscopic life living on its surface. Over time, the cardboard disappears and is converted into dark, rich vermicompost and worm castings.

Cardboard is made primarily from plant fibers, so it becomes another form of organic material inside the bin. Corrugated cardboard is especially useful because its fluted center creates small spaces where air can move through the bedding.

Why Cardboard Makes Such Good Worm Bedding

A worm bin needs more than food scraps. The worms also need a moist, breathable environment where they can move around, escape concentrated pockets of food, and receive enough oxygen.

Cardboard helps create that environment in several ways.

It Holds Moisture

Composting worms breathe through their skin, so they need moisture to survive. Damp cardboard absorbs and holds water without immediately turning into mud.

The goal is not to make the bedding dripping wet. It should feel like a wrung-out sponge. When you squeeze a handful firmly, you should see only a few drops of water. If water streams out, the bedding is too wet.

It Creates Airflow

One of the most common mistakes in a worm bin is allowing the bedding to become wet, heavy, and compacted.

Worms need oxygen just like we do. Shredded corrugated cardboard creates texture and small air pockets throughout the bin. This helps keep the bedding loose and reduces the chances of it becoming anaerobic, which is often when a worm bin begins to smell bad.

It Balances Moist Food Scraps

Most kitchen scraps contain a lot of water and nitrogen. Cardboard is a dry, carbon-rich material that helps balance those scraps.

If a worm bin is getting too wet, adding dry shredded cardboard can absorb some of that extra moisture. It can also help cover exposed food, reduce odors, and make the bin less inviting to fruit flies.

It Gives Worms a Safe Place to Live

Food scraps can sometimes become acidic, ferment, or briefly heat up as they begin decomposing. Bedding gives worms somewhere to move when conditions around a pocket of food are not ideal.

I like to think of food as the kitchen and bedding as the rest of the house. Your worms need both. A bin filled almost entirely with food does not give them enough safe living space.

It Is Inexpensive and Sustainable

Cardboard is one of the most affordable bedding materials available because most households already have it.

Using cardboard in a worm bin also gives it another purpose before it becomes finished compost. Instead of purchasing all-new bedding, you can reuse something that may otherwise be thrown away or recycled.

What Kind of Cardboard Should You Use?

Plain brown corrugated cardboard is generally the best choice.

Good options include:

• Plain shipping boxes
• Brown corrugated boxes
• Cardboard egg cartons
• Paper towel and toilet paper rolls
• Plain paper drink carriers
• Uncoated brown paper bags

Before using a box, remove:

• Packing tape
• Plastic shipping sleeves
• Staples
• Foam
• Stickers and labels
• Any other non-cardboard material

A small amount of ordinary printing is generally difficult to avoid, but I prefer using the cleanest, plainest cardboard available.

Avoid cardboard that is glossy, wax-coated, waterproof, heavily laminated, covered in foil, or contaminated with chemicals or greasy food. If you are unsure whether a piece belongs in the worm bin, it is perfectly fine to leave it out.

How to Prepare Cardboard for Worm Bedding

You do not need any expensive equipment to prepare cardboard. You can tear it by hand, cut it into strips, or use a heavy-duty shredder made to handle cardboard.

Here is the simple method I recommend:

1. Remove the Tape and Labels

Go through the cardboard carefully and remove anything that will not naturally break down. It is much easier to do this before the cardboard becomes wet.

2. Tear or Shred the Cardboard

Tear the cardboard into small strips or pieces. Pieces approximately one to three inches across work well, but they do not need to be perfect.

Smaller pieces absorb moisture more evenly and break down faster. They are also easier to mix into the bin without creating large, matted sheets.

3. Soak the Cardboard

Place the shredded cardboard in a bucket or tote and cover it with water. Let it soak until it becomes soft and completely moistened.

Depending on the thickness, this may take about 10 to 20 minutes. Thick corrugated cardboard may need a little longer.

4. Squeeze Out the Extra Water

Take handfuls of soaked cardboard and squeeze out the excess water. The finished material should be thoroughly damp but not dripping.

Remember the wrung-out-sponge rule: when you squeeze it firmly, only a few drops should come out.

5. Fluff It Up

Pull the wet pieces apart and fluff them before placing them into the bin. This is important because a solid mass of wet cardboard can compact and limit airflow.

6. Add It to the Bin

For a new worm bin, begin with approximately four to six inches of loose, damp bedding. Do not press or pack it down.

I also like mixing cardboard with another bedding material, such as aged compost, shredded paper, dry leaves, coco coir, or a small amount of finished worm castings. Using a mixture creates different textures and helps keep air moving through the bedding.

Can You Use Dry Cardboard?

Yes, dry cardboard can be extremely useful in an established worm bin.

If the bin is too wet, mix in handfuls of dry shredded cardboard. It will begin absorbing excess moisture almost immediately.

Dry cardboard is also helpful when adding watery foods such as melons, cucumbers, tomatoes, or thawed frozen scraps. Place some dry cardboard underneath or around the food to help manage the extra liquid.

However, when starting a new bin, I recommend moistening the cardboard first. Completely dry bedding can pull moisture away from the worms and will not provide the comfortable environment they need.

How Much Cardboard Should You Add?

There is no single amount that works for every bin. The right amount depends on the number of worms, the size of the container, how much food you add, and how much moisture the food contains.

Your bin should always contain visible bedding—not just food and castings.

Add more cardboard when:

• The bedding is disappearing
• The bin feels too wet
• The contents are becoming dense or compacted
• Food scraps are exposed
• You notice unpleasant odors
• Fruit flies are becoming a problem
• You harvest castings and remove old bedding

I would rather see a beginner use a little too much bedding than too much food. Extra cardboard gives the worms room to move and helps create a more forgiving environment while you learn how the bin behaves.

Use Cardboard to Cover Each Feeding

After burying food scraps, cover the feeding area with a layer of moist or dry shredded cardboard.

This simple step can help:

• Control odors
• Discourage fruit flies
• Absorb moisture from the food
• Keep the surface dark
• Maintain a healthy carbon balance
• Provide additional bedding as the old material breaks down

You can also place a flat piece of damp cardboard across the top of the bedding. Worms often gather directly underneath it because that area stays dark and moist.

Check beneath it occasionally, replace it as it breaks down, and make sure it is not forming an airtight mat over the entire surface.

Common Cardboard Bedding Mistakes

Cardboard is simple to use, but a few mistakes can create problems.

Making It Too Wet

If the cardboard is dripping, the bottom of the bin may become waterlogged. Wet bins lose airspace and may begin to smell.

Packing It Down

Always fluff the bedding. Worms need moist bedding, but they also need air moving through it.

Using Only Tiny Paper-Like Shreds

Very fine material can clump together when wet. Mixing different sizes and textures helps prevent compaction.

Forgetting to Add Fresh Bedding

Cardboard does not last forever. The worms and microorganisms continually break it down, so it must be replenished.

Using Coated or Contaminated Boxes

Plain brown cardboard is the safest and simplest choice. Avoid waxed produce boxes, glossy packaging, chemical containers, and greasy or heavily soiled cardboard.

Cardboard Is Bedding and Eventually Becomes Food

This is one of the most important things to understand: cardboard serves two purposes.

At first, it provides moisture, structure, airflow, darkness, and living space. As it softens and decomposes, it gradually becomes part of the worms’ food supply.

That is why it is so useful. It helps create the right environment today while eventually becoming part of the finished vermicompost tomorrow.

My Final Advice

If you are just beginning with composting worms, do not feel like you need to purchase a complicated mixture of expensive bedding ingredients. Start with plain brown corrugated cardboard, prepare it correctly, and pay attention to moisture and airflow.

Give your worms plenty of bedding, feed conservatively, and add more cardboard whenever the bin starts becoming wet or compacted. A healthy worm bin should smell earthy—not sour or rotten—and its contents should feel damp, loose, and full of air.

Cardboard may not be the most exciting part of raising composting worms, but it is one of the most valuable. Sometimes the best material for your worms is already sitting in your recycling pile.

—Calvin
Utah Worm Company