Opening up the world of decay and rot

I’ve often commented on not leaving trash outside. I have explained that trash is dangerous to animals and birds. We have taken a plastic bag with us as we go for a walk and have picked up trash left by others. This is especially needed after New Year to clean trash created by fireworks and is a lot of fun for the kids.

I wanted to expand on this topic and introduce topic of decomposition (in Finnish: maatuminen). Decomposition is a process through which organic matter decomposes / is broken down into smaller particles. This happens through a) autolysis = living matter no longer living starts to break down, and b) putrefaction = bacteria and fungi break down previously living matter. Decomposition is something that happens to organic tissue meaning animals, plants etc. It does not happen to rocks or metals. It hardly happens to plastics either, which is why we have so much of plastics in our oceans and lakes etc. The plastic does break down into micro plastics (really small pieces of plastic) but it does not go away completely. Plant matter on the other hand decomposes and makes up new soil with plenty of nutrients.

To introduce this topic, we built a decomposition box. I took a plastic box with a lid. In this box we put plant matter, mainly potato and carrot peelings, which I happened to have around as I had made food with carrots and potatoes that day, and some cut flowers and stems etc. We also put in some tissue, toilet paper, cardboard, two plastic caps, a few rocks and a bit of tinfoil. Cutting stuff up was a lot of fun for my daughter so we took our time and filled the box entirely. As we were cutting stuff up and stuffing the box, I asked my daughter to make a hypothesis (= evidence based guess) about what would decompose and what would not. She thought about it and said that the plant stuff, tissues, toilet paper and cardboard would decompose, but rocks and plastic would not. She also thought the tinfoil would decompose. I just said that we would have to wait and see.

Decomposition experiment

Experimenting with decomposition: Put some plant matter, some plastic, rocks, paper, cardboard, tinfoil etc. in a plastic box and let decay.

We then placed the box outside in our garden shed and came back to it after one week and then after two weeks. First thing we noticed was that there was liquid on the sides and on the lid of the container and stuff just started to, well, decompose. We did not open the container, but let bacteria do their stuff.

Image shows the Decay box after two weeks. Liquid has condensed on the sides of the box and decomposition processes have begun.

Decay box after two weeks. Liquid has condensed on the sides of the box and decomposition processes have begun.

Then I (and therefore we) pretty much forgot about the entire experiment for about two months. I was supposed to take a picture of the box each week, but oh well. Life and such. Luckily this is an experiment where it does not really matter. After I again remembered about the experiment, the decay had progressed and the box looked like this:

Image contains the decay box, which is filled with brown stuff and liquid

Decay box after 2-3 months. Decay is quite far gone and different materials are hard to identify.

Finally it was time to end the experiment. The decay box had had three months of basically neglect and decay had progressed quite well. That is the thing with decay and decomposition. It happens on its own. Then we took some sticks, because there was no way I was touching that stuff or let my kid either. Before opening the box I reminded her what we had put in the box and what she had thought would compose and what would not compose. I asked her again what she thought would compose and she pretty much gave the same answer, but left out tinfoil altogether. Then we poked about in the box:

End result of the decay box. Plastic, rocks and tinfoil clearly visible, other stuff brown and decayed

End result of the decay box

Plant matter, tissues and cardboard had decayed into brown stuff. It is still quite far from soil, but clearly changed. Plastic caps, tinfoil and rocks (the red object between tinfoil and plastic cap in the image) were completely unchanged. I asked my daughter why she thought that tinfoil had not decayed. To this she could reply that it was made of metal. Metals do not decompose.


If you try these experiments at home and your child asks questions, please let me know what types of questions they ask in the comment section so I can further develop these instructions. If you have questions about these experiments or instructions, leave me a comment and I will answer and also improve these instructions. Also, please remember like and share if you find this useful.

Copyright text and images: Satu Korhonen. You are free to try these experiments out, use them in your teaching. But instead of copying the text or images, link back to this page.

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