Making compost with cardboard

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Making compost with cardboard

I can remember when I was a child, receiving a much valued item that came in a cardboard box. The contents would be taken out, with great care and would be the focus of my attention. There was a limit to the attention that the contents would have because, sooner or later, for some unexplainable reason, my attention would switch to the box. 

There’s something about a cardboard box that reaches out to a child’s imagination. But when all aspects of how it could be used or what it could possibly represent in a child’s world, have been exhausted, we go back to the basics of, ‘it’s a just a cardboard box’.

So, then we get to the bit where we decide how we’re going to dispose of the cardboard box. For most people the easy way is to flatten out their old boxes and put them out with the trash. We could go on about what percentage of landfill is made up of cardboard but we don’t need to. Let’s just say, it’s a lot. 

For those who plan and prepare, there is the option of sorting it into the right categories and sending it off for recycling. Recycling of cardboard does appear to be a viable option. Many of the cardboard boxes that we handle have been reduced to pulp then turned into ‘new’ cardboard. I would suggest that this should be our first option.

Here at Rolypig.com we consider all things composting. The obvious question for us then, is, can you put cardboard on compost? 

Cardboard will turn into compost. Some boxes are quite big. Can such a big and bulky item be converted into something as useful as compost?

It will rot if it’s allowed to become wet. It works well in any composting system. To get the best results it will help if you break it down or shred it into small pieces. This applies to most things that go into the compost bin, heap or pile. If you find it a struggle to cut a big box into small pieces, make it wet. Soggy cardboard will fall to pieces in your hands. 

Making compost from cardboard

There are no rules that say that cardboard has to be dry when you load it into the compost. Wet, mashed up, cardboard will work just as well as dry. It’s all going to get wet or damp as the compost forms. 

Cardboard is the perfect ‘carbon brown’. It ranks along with dead leaves and sawdust. You need a good supply of ‘carbon browns’ if you’re making compost from food waste. 

It makes sense to keep a store of flattened cardboard boxes for the purpose of ripping into pieces and adding it to the compost as you need it.

Is cardboard safe for compost?

I’ve used cardboard in compost for a long time and there’s never been any problems that have left me wondering about cardboard being safe for compost. We could question the effects that cardboard-glue may have but the quantities of this are so small that it’s difficult to see how it can have any adverse effect. 

Unless you have a piece of cardboard that’s been soaked in something that’s likely to inhibit the natural progress of composting, there shouldn’t be a problem. Even then, there are very few substances that we have access to that will render cardboard non compostable. The variety of microorganisms that reside in compost will overcome most substances, however challenging they may be.

Make compost from cardboard or recycle?

Is it better to compost recycled cardboard?

It makes no difference whether you have new cardboard or recycled. Either can be turned into compost. 

If you are skilful enough to identify that the cardboard you have is new rather than recycled, then send it to be recycled again if you can. It’s much better to make use of it for the initial purpose that it was intended for rather than sending it to a rotting heap.

Strong, solid cardboard will be more likely to be accepted for recycling. It will have ‘life’ left in it and will be worth pulping to be pressed out into ‘new’ cardboard. Soft and floppy cardboard has probably been recycled for the last time. 

You can tell if a box feels particularly weak and floppy. If they tear up easily and feel soft, these boxes can be torn up and put with the compost.

Is all cardboard recyclable?

All cardboard is recyclable. But there is a limit as to the number of times cardboard can be pulped again and put through the cardboard making process. This is due to the fibres in cardboard becoming shorter. Every time cardboard is recycled, the fibres are reduced in length and the cardboard loses its strength. 

Without a viable fibre content in the pulp, it’s difficult to establish a good quality, strong cardboard. Unless there is some other use for pulp that has little or no fibre content, when cardboard has reached its last use as cardboard, it will have to be dumped.

How long does it take to compost cardboard?

For cardboard to compost fully it will take a minimum of 4 months. This is the time it will take if there are no worms present. I notice in the Rolypig composter, cardboard will break down and disappear very quickly. This is because the Rolypig has a strong population of worms in it. The worms don’t need to wait for cardboard to rot before they start to eat it. When cardboard becomes wet, it’s soft enough for them to consume and they will do so very quickly. Wet cardboard can be reduced to worm casts in less than a week.

Can I compost cardboard egg cartons?

Cardboard egg cartons can be composted but you may find that these may be increasingly difficult to get hold of. Many egg cartons, these days appear to be made from transparent plastic.

Egg cartons that are made from cardboard, tend to be made from material that  has been recycled many times previously. You can tell by the look and feel of the carton quality.

The same applies to:

  • Toilet roll centres, these are compostable.
  • Cardboard food boxes, all compostable.
  • Pizza boxes, these may have remains of pizza in them. This would make composting the cardboard box an ideal option.

 Are Amazon boxes compostable?

Amazon tend to send a box that’s much bigger than the contents would initially need. This is actually done for efficiency reasons. If the box looks like a solid box and the cardboard feels of good quality; they usually are, then send it to be recycled.

Recycling an Amazon box is my first choice. Only send the weak and flimsy boxes to the compost heap.

Can you compost shiny cardboard?

Cardboard that’s got a shiny surface is usually high quality. You may want to consider sending this to be recycled as this would be a more productive use for it.

If that isn’t practical to do, then it will decompose and make compost. It may take a little longer because the shiny surface-finish will make the cardboard, up to a point, water proof. The smooth shiny surface on cardboard is achieved by using a process in the manufacture. It’s very similar to glossy magazines. The shiny surfacing process involves the adding of clay. This makes the surface tougher in addition to being shiny.

The clay factor involved here will not prevent the cardboard from breaking down completely. When enough moisture has gone into the shiny layer, the worms will be able to use the clay ingredient, because clay particles in a worm, aids the digestion of organic material.

Is waxed cardboard compostable?

Cardboard that’s coated in wax can be composted. Waxed cardboard can’t be recycled and made into new boxes because the wax can’t be separated. Any attempt to make recycled cardboard wouldn’t work. 

The fibres wouldn’t be able to stick together because there would be enough wax in the mix to keep them apart. Trying to make recycled cardboard from waxed cardboard would be like trying to nail jelly to a wall.

As for putting waxed cardboard in compost, there are no reports from anywhere that the wax on cardboard has any adverse effect on the composting process. Wax is an energy material and falls under the category of oil. Oil is often placed in the general pollution category but it’s amazing how microbes will consume it, provided that the conditions and concentrations involved are favourable.

Why do paper milk cartons take so long to decompose?

There was a time when drinks cartons were wax coated. They would hold in the liquid very successfully and no one complained. These cartons could be turned into compost and everyone was happy. 

These days, many cardboard drinks cartons have a layer of low density polyethylene (LDPE). For anything that’s going to hang around in storage for a while, there’s an inner lining of aluminium foil. This is to prevent the liquid product from having direct contact with the cardboard. 

Any such contact will, over time, risk a reaction between the two which may affect the flavour of the product.

It’s these added components that have the effect of preserving the carton when we may be trying to get them to rot down. When you look at an empty milk carton, it’s not immediately obvious that it’s not suitable for composting. They all look like the waxed cardboard cartons that we’re, historically, used to.

So, if you see a milk carton in the compost and it doesn’t appear to be making any headway in terms of rotting into oblivion, this is probably because a combination of polyethylene and aluminium are protecting the cardboard element. You will probably need to remove this from the compost and send it to landfill with the rest of the trash.

To avoid the problem you need to establish the make-up of the cartons that you’re handling. Then find out if there is an option, in your area, to recycle these types of cartons. 

The service to do this may not be everywhere. There are recycling plants that specialise in separating the cardboard element from the polyethylene and aluminium.

There is another breed of carton that’s worth looking out for that does away with the problem completely. This involves cardboard cartons having a layer of what’s become known as, ‘bio-plastic’. This isn’t plastic as we’ve always known it. It’s made from corn starch, making it ‘vegetable’ rather than anything man-made or synthetic.

A cardboard carton that has corn-starch added to take the place of polyethylene, is made for composting, after use. This is an ideal solution for those who are committed composters. 

There’s a standing debate about the whole subject of cardboard composting. Some see the composting route as a waste of a resource. They argue that cardboard, regardless of the extra components of polyethylene and aluminium, should be recycled. Cardboard can be recycled over and over again. Turning it into compost could be seen as a wasted opportunity of extended use. 

Image sources

Cardboard boxes

What else would you like to know?

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