It’s no secret that cardboard is in no short supply. 41 percent of all solid waste in the United States is cardboard. This all-too-familiar brown paper product is used to transport nearly 90 percent of global shipments. When we go grocery shopping, a huge chunk of what we buy is packaged in this remarkably abundant resource. Fortunately, it’s also one of the most recycled items on the planet.

If you have a garden, you’ve probably also got yourself a compost pit, pile, or compost bin. Tending to your compost’s carbon-to-nitrogen ratio is the only way to produce rich, hot compost that will keep your plants happy and healthy. Compost should have a ratio of 30 parts carbon to every part nitrogen. Of course, you probably know this already.

Cardboard is an excellent source of carbon. Cardboard itself has a carbon-to-nitrogen ratio of roughly 250;1. Not all cardboard is created equal, however. If you want to start composting with cardboard, you’ll want to become acquainted with what types of cardboard can be composted, how to properly process the cardboard for your pile, and how much you need to add so you don’t overwhelm your compost’s carbon levels.

Let’s take a little stroll down compost lane together and get acquainted with the ins-and-outs of composting cardboard. I hope you brought your shovel!

Types of cardboard to compost

Not all cardboard is created equal. There are three main varieties of cardboard with varying degrees of compostability. Composting cardboard isn’t necessarily a free-for-all. It’s important to be aware of the variations before throwing all your cardboard straight into your pile.

Corrugated cardboard is your most common type. You might even say your garden variety. Think pizza boxes and shipping boxes. You likely have a copious supply of these lying around if you buy a lot of things online or order a lot of take-out. This type of cardboard is made with three layers. Two outer layers of thin cardboard enclose a ruffled piece creating the tell-tale corrugation pattern.

If your planning on composting cardboard, this is your most ideal variety as it is easy to process and has few adulterants. If you don’t have a lot to work with, you can always find a cornucopia of corrugated cardboard at retail establishments and restaurants. Ask a manager if you can recycle some of their cardboard boxes for your garden. Most businesses will be more than happy to part ways with a reasonable quantity if you ask nicely.

Paperboard is another type of cardboard that is easy to find as long as you know what you’re looking for. Shoe boxes, cartons, cereal boxes, and other food packaging are typically made of this kind of cardboard. Similar to corrugated cardboard in many ways, paperboard lacks the inner ruffled layer. Paperboard is composed of one sheet of stock. It’s easier to shred than corrugated cardboard but suffers by its tendency to being covered with undesirable additions such as inks and laminations.

Coated Cardboards have additional layers of wax or plastic added to increase their durability. These are used frequently to ship produce. They break down slower than corrugated cardboard or paperboard and thus they are the least sought after for compost. Some wax coatings are biodegradable so they can be used sparingly, while others are coated with petroleum-based plastics which you definitely don’t want in your garden soil.

Be sure that you never use foil-covered cardboard. Some food items and pet supplies use a layer of aluminum foil to preserve their contents. You might be able to peel this nuisance layer off before shredding the cardboard, but if it’s really stuck on there it’s not worth potentially harming your plants. Scrap it.

Processing your cardboard

You might be tempted to throw entire boxes into your compost and call it a day. Cardboard, unfortunately, takes quite a long time to break down without a little bit of processing. You want your pieces to be as tiny as possible. This sounds easier than it sounds. If you were to sit down and try to tear apart a cardboard box you’d quickly wind up with hand cramps and frustration.

Fear not my green-thumbed knowledge seekers. There a few things you can do that will lessen the burden of this process. You’ll still need to retain a bit of patience but I promise you that this is a situation where your patience will pay off.

First of all, make sure you remove all packing tape from your cardboard, especially if it was used as a shipping container. The tape is made of plastic and does not break down. Be on the lookout for stickers or shipping labels as well. You want clean cardboard for your compost. Brown cardboard is preferred as it is unbleached.

If you are using corrugated cardboard, you can actually separate it’s three laters pretty easily by starting with a corner and peeling. This will greatly aid in your shredding process.

Invest in a good set of scissors or shears if you don’t already have them. You’re going to want something a bit more heavy-duty, so forget about those safety scissors from grade school. Fiskars makes a great line of rugged scissors for cutting things with a thickness at a quickness.

Cut the cardboard into strips no bigger than 1″ thick. Try to keep their length short as well, aiming for 2″ to 4″ tops. The smaller your shreds, the faster it will break down, and the easier it will be to incorporate into your soil.

If you are struggling with cutting your cardboard by hand, you can try wetting it first. Carboard becomes quite flimsy when it is saturated. You can lay it flat and use an Exacto knife or a razor blade to cut into strips before shredding it finer. Take your time. This isn’t a race.

Some gardeners have repurposed electric paper shredders to aid in their cardboard shredding. Make sure that whatever shredder you attempt to use is suited for heavier tasks. Some are designed with this sort of functionality in mind. Don’t try to shred large pieces at once as this might put your shredder under too much strain and burn out its motor. This is the least advisable suggestion as it may potentially damage your equipment. Approach at your own risk and with some common sense.

Mixing cardboard into your compost

Cardboard alone won’t produce compost. As we already discussed, compost requires a delicately intentional blend of carbon and nitrogen-heavy ingredients for optimal results. With the right recipe, however, cardboard is an extremely useful ingredient.

There are two color-coded components to compost. Brown ingredients are carbon-heavy like leaves, sawdust, pine needles, ashes, paper, and peanut shells,

Green ingredients are nitrogen-heavy and they include things like fruit scraps, vegetable scraps, lawn clippings, tea bags, and coffee grinds.

Cardboard is of the brown variety. If you don’t get your ratio quite right, your compost will develop slowly. You might also notice a rather offputting aroma.

It’s recommended that for every part green, you add three to four parts brown. You’re not just making a compost salad. Instead of mixing your cardboard with your green material, it’s beneficial to layer it.

  • start with 2″ – 4″ of cardboard shreds
  • add 1″ – 2″ of green material (like food scraps)
  • cover with a thin layer of potting soil
  • turn your pile with a pitchfork or shovel every 3 to 4 days
  • repeat

If you aren’t producing enough green compost material a day to layer in this fashion, make sure that when you add your green material to your pile that you add 5 or 6 handfuls of cardboard for every cup of compost you add.

Keep your compost moist. It should be about as wet as a sponge, but should not be wet enough to start pooling. Water your compost with a hose if you need to. Your cardboard will surely absorb quite a bit of water. Moisture is vital for producing rich nourishing compost.

Cardboard Lasagna

Another way you can add cardboard to your garden and avoid having to till is by layering cardboard over grass or dirt and covering with a nitrogen-rich material like manure. You can add another layer of cardboard and manure if you desire before covering your layers with mulch and potting soil.

We already talked about how cardboard takes quite a long time to break down. If this lasagna layering technique serves as the base of your garden, over time the cardboard will eventually break down and turn to compost. In the meantime, this slow-to-degrade layer protects from grass and weed infiltration.

You can grow your own way

There is certainly a deep sense of satisfaction that comes with gardening. This sense of bliss is accentuated when you are able to add an extra layer of sustainability to the mix by recycling. There is no sense in letting all that usable cardboard pile up or go into your burn barrel when you could be using it to make killer compost.

Be patient, compost takes up to a year before its good enough to be mixed with your soil. There is no one right way to garden or to compost. You may need to experiment a bit and figure out what works best for your locale and climate. If you follow these simple suggestions, however, you’ll surely add an extra tool to your ever-growing gardening arsenal.

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