Composting cardboard is a great way to get rid of old boxes that are taking up space in your home. Composting is environmentally friendly because it keeps the boxes and other paper products out of the landfill. They turn into nutrient rich hummus that you can use in your garden. They don’t release any harmful greenhouse gasses into the air or toxins into the soil. In this guide, I’ll explain how to compost cardboard boxes and paper for best results. I’ll also share some benefits and drawbacks of composting these materials.
Can You Compost Cardboard?
Yes. You can compost cardboard. It is made from organic materials that naturally break down over time. It will decay into nutrient rich compost that you can use in your vegetable garden and flower beds.
In composting, there are ‘brown’ materials and ‘green’ materials. Cardboard is considered a brown material because it is rich in carbon. To compost cardboard waste, you will need to mix it with some green materials, which are rich in nitrogen.
Which Types of Compost Can You Compost?
There are different types of cardboard. Not all are compostable.
- Corrugated cardboard can be composted if it is cut into small pieces. For example, you can compost moving boxes and most Amazon boxes.
- Flat cardboard like you would find in cereal boxes and shoe boxes can also be composted.
- Pizza boxes, even if they’re coated in grease, can be composted
- Toilet paper rolls and paper towel rolls can also be composted
Types of cardboard that you shouldn’t compost
- Cardboard that has been coated with plastic, wax, or metal foil shouldn’t be composted. Examples include plastic cups, ice cream containers, and some pet food bags. If you really want to compost these items, you can but you will need to remove the coating first. This could be a job.
- Cardboard that is covered in plastic tape or stickers shouldn’t be composted unless you remove them first.
- Cardboard that is coated in heavy dyes, like beverage containers, shouldn’t be composted.
- Whole boxes shouldn’t be composted. They need to be broken down first.
Why Compost Cardboard?
Composting cardboard keeps it out of the landfill. This is important because cardboard and paper make up about 26% of all municipal waste according to this interesting article. Landfills are some of the biggest emitters of methane and carbon dioxide. As waste decays, it releases gasses. Reducing the amount of cardboard in the landfill helps reduce the emission of greenhouse gasses.
Cardboard is also an excellent brown material to use to balance out green materials in your compost. Brown materials provide carbon while greens provide nitrogen. You need browns to balance out the greens. Some great green materials include grass clippings, kitchen scraps, and coffee grounds. Both types of materials are necessary to make quality compost.
Cardboard makes great compost. It does a great job of retaining moisture. Cardboard also gives your compost some structure. It helps create air pockets so your compost stays oxygenated. You can use the compost in your flower beds and vegetable gardens.
Why Not to Compost Cardboard
The only reason not to compost cardboard is because certain types of cardboard can introduce toxins into your garden. They can release heavy metals and petroleum products as they degrade. These toxins come from coating or ink on the cardboard, not the cardboard itself.
If enough of these toxins build up, they could harm your plants and slow their growth. They will stay in the soil for many years. For this reason, you have to be careful about the types of cardboard that you compost. It’s best to only compost clean cardboard that doesn’t have any type of coating or printing on it.
Some gardeners claim that you shouldn’t compost cardboard because it can contain formaldehyde. This can be a problem because formaldehyde can kill certain beneficial bacteria and fungi. This could slow down the decomposition process. The good news is that formaldehyde is a volatile substance. Most of it will break down and dissipate away before it contaminates your soil.
Composting Cardboard Vs Recycling
Most cardboard can be recycled or composted. Generally, composting is the more environmentally friendly option. It is clean and it doesn’t waste any resources. It doesn’t release anything harmful into the soil or use any fossil fuels. The cardboard decays into a nutrient-rich hummus that you can use to feed your plants.
Recycling is also a good option but it’s not as environmentally friendly. One problem with recycling is that some of the cardboard doesn’t actually get recycled. It ends up in a landfill somewhere or it gets burned. Sometimes recycling just isn’t economical.
Also, recycling itself isn’t the most environmentally friendly process. A lot of water and fossil fuels are required to process post-consumer paper into new products. Recycling plants actually use more fossil fuels than paper mills. The process of recycling paper also creates byproducts that are difficult to dispose of. If you want to save the environment, you’re better off reducing the amount of paper products that you use.
How to Prepare Cardboard to Compost
- Sort the cardboard- Before you start the composting process, remove any cardboard that has a glossy coating or excessive printing. Ideally, you should only compost clean cardboard. If it has a bit of printing on it, it’s okay.
- Clean the cardboard- Remove any materials that won’t decompose such as tape, staples, stickers, foil liners, cellophane, etc. If you’re not sure, remove it. You don’t want these in your garden because they could break down into microplastics or they could release potentially toxic chemicals.
- Break the cardboard into small pieces- Smaller pieces will decompose faster because they have more surface area for the microorganisms to work on. Small pieces are also less likely to clump up. If the cardboard is thin, you can tear it up with your hands. If it’s thick, you may need to use some scissors, shears, or a box cutter to cut it up. You can also soak the cardboard in water to make it easier to tear apart. You could also use a paper shredder if you have one that is powerful enough to shred cardboard.
How to Compost Cardboard
- After the cardboard is clean and cut into small pieces, you can add it to your compost heap. If you’re starting from scratch, add a layer of shredded cardboard that is about 4” thick. Add some other high-carbon materials such as shredded dried leaves, straw, wood chips, or ash. These carbon-rich materials are referred to as ‘browns’ in composting.
- Next, add some water. The pile should be moist but not wet. It should be about as damp as a sponge that has been wrung out. Microorganisms need a moist environment to start decomposing the cardboard, food waste, and other organic waste.
- Next, add a 4 inch layer of nitrogen-rich materials on top of the cardboard. You could use food scraps, coffee grounds, grass clippings, etc. These nitrogen-rich materials are referred to as ‘greens’ in composting.
- Continue adding more layers of brown and green materials. When you’re done, you can add a layer of soil on top if you choose but it is not required. This layering method is sometimes referred to as the lasagna method.
- After 5-7 days aerate the compost. Use a pitchfork to turn the compost. This will help add oxygen to your compost. The beneficial microorganisms need oxygen to decompose the cardboard and other materials. Aerating your compost can also help prevent it from matting. You should aerate your compost once every 5-7 days.
- Water the compost when it starts to get dry. You should check on it every 3-5 days to make sure it’s not drying out. When it is, use a hose or watering can to dampen it. You can use rainwater or regular tap water. Rainwater is preferable because more neutral. Be careful not to add too much water. You just want the compost to be moist, not completely wet. If you add too much water, it could start to smell and mold and attract pests. The best way to tell if your compost is too wet is to pick up a handful and squeeze it. If a few drops of water come out, it is the correct dampness. If water runs out, it’s too wet.
- Add materials as they become available. When you have some new kitchen scraps or yard waste, add them to your compost. Ideally, your compost should be 2-3 parts brown materials for every 1 part green materials. If you add too many greens, the compost will become a sloppy mess. If you add too many browns, it will take a long time to decay.
Other Ways to Compost Cardboard
Another way to compost cardboard is to start with a layer of sheets of cardboard at the bottom of the pile. You can then build a regular compost pile on top of it. Alternate green and brown materials. You can mix in more shredded cardboard if you choose. Over time, the cardboard at the bottom will slowly break down and become part of the pile.
You can also add a layer of cardboard sheets to the bottom of raised garden beds. The cardboard will help with weed control. Over time, it will decay away and add some organic material to the soil. The cardboard will also help hold some moisture. You can add several layers but you don’t want to add too much cardboard or it will take too long to decompose.
You can also place cardboard under your mulch. The cardboard will keep the weeds down. It works as a weed barrier, like landscape fabric. The mulch will hold the cardboard in place. Over the course of a year or so, the cardboard will decay away. For more info on this technique, check out my guide to sheet mulch.
Can You Compost Cardboard With a Glossy Coating or Printing On It?
Most people don’t compost cardboard that has a glossy coating or printing on it. The reason is that the inks and adhesives used to make these can contain petroleum products and pigments with heavy metals. They are not made from natural materials. If you compost these types of cardboard, they could contaminate your soil with potentially harmful chemicals. These chemicals would stay in the soil for a long time.
These days, you can compost some glossy and printed cardboard. Many companies are switching to more environmentally friendly inks and adhesives that are made from organic materials. They contain fewer harmful chemicals and are more environmentally friendly. They break down naturally. You could compost these if you choose. Some people do.
It is also possible to remove the coating in some cases. You may be able to wet the cardboard and scrape it off with a knife. If there is a foil coating, you may be able to separate it from the cardboard and tear it off. If you can remove the coating, you can compost the cardboard. Sometimes, it’s more hassle than it’s worth.
Personally, I don’t compost shiny cardboard if it has a glossy texture or if it has too much ink on it. I also remove any tape, stickers, or adhesive before composting it. I try to only compost clean cardboard. If it has a little bit of printing on it, I will sometimes still use it.
Composting Other Paper Products
You can compost other paper products such as newspapers and office paper. Junk mail is great for composting as well. Shred the paper and add it to your compost, just like you would use cardboard. Avoid composting glossy paper or paper with too much ink.
How Long Does it Take for Cardboard to Turn Into Compost?
In good conditions, it will take around 6-8 weeks for cardboard to turn into nutrient-rich compost. In less-than-ideal conditions, it may take 3-6 months. When composting in poor conditions, it could take one to two years before the compost is ready.
Exactly how long it will take for the cardboard to turn into compost depends on the type of cardboard and how active your compost bin is. Thinner and lighter cardboard will decay faster. Hot and active compost bins will also decompose cardboard faster than cold compost bins.
My Experience
If I buy a product that comes in a cardboard box, I often use the cardboard for compost. I only add clean cardboard to my compost. If it has some printing on it or if it has a glossy coating, I recycle it or throw it away. Before adding the cardboard to my compost, I remove any tape or labels and make sure it doesn’t have too much ink. I then cut it into smaller pieces. When I’m making a new compost bin or raised garden bed, I will line the bottom with a layer of cardboard. I also used some cardboard under my mulch when I expanded my garden.
Cardboard can make great compost. It can add some valuable nutrients to your compost. It also adds organic matter, which helps retain moisture. The resulting compost can be used in your flower beds and vegetable garden. Compost can help your plants grow stronger and healthier.
Do you compost cardboard? Share your experience in the comments below!
More from The Homestead Hangout!