Biodegradation Experiment Kids Can Bury for 60 Days

The US Federal Trade Commission has a rule about the word “degradable”. A marketer may not use it without qualification unless the whole product “will completely break down and return to nature within one year after customary disposal”. Read that, then look at the compostable bag in your kitchen drawer. This biodegradation experiment kids can run with a trowel and a kitchen scale puts that claim on trial: five materials, one flower bed, sixty days, and a weighing at the end. The result is usually not what anybody predicted, and the item people are most confident about is usually the one that disappoints.

Key Takeaways

• You will bury five labelled materials in mesh bags 15 cm deep, dig them up after 60 days, and compare dry weight before and after.
• The concept is biodegradation: microbes only break down polymers whose bonds their enzymes can cut, which is why cotton vanishes and polyethylene does not.
• Best for ages 7 to 14. Younger children handle the digging and photographing; older ones do the dry-weight maths and the percentage loss.
• The usual failure is losing the samples. Use mesh bags and a map, or you will spend an hour sifting soil in November.
• Sixty days is deliberately short. Some items will barely change, and that honest null result is the point.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Mesh bags	5, fine nylon	Laundry bags, or cut-up tights	Onion net bags, but mesh under 2 mm is better
Banana peel or apple core	1 piece, about 20 g	Kitchen	Lettuce leaf, carrot peel
Cotton square	10 × 10 cm, 100% cotton	Old T-shirt	A cotton cloth offcut. Avoid blends
Newspaper	One 10 × 10 cm square	Recycling	Plain uncoated paper
”Compostable” or “biodegradable” plastic	One 10 × 10 cm square	A compostable bin liner, a starch cutlery fragment	Any item labelled biodegradable
Ordinary plastic	One 10 × 10 cm square	A supermarket carrier bag or PET bottle wall	Any unlabelled plastic film
Kitchen scale	0.1 g resolution	Kitchen	A 1 g scale works, use bigger samples
Trowel, gloves, labels, ruler, phone camera	1 each	Shed and drawer	Plastic plant labels beat paper ones

Time: prep 30 min, then 5 minutes at each of four check-ins, 45 min at the dig-up Cost: everything is probably in your kitchen, plus a packet of mesh bags Mess level: do this outside

Do the Experiment

Step 1 — Dry, weigh and photograph every sample

Leave all five items somewhere warm and airy for 24 hours so they start at a comparable dryness, then weigh each one to 0.1 g and write the number down. Photograph each next to a ruler on a plain background. The banana peel will lose a lot of water weight on its own, which is exactly why the starting dry weight matters.

Step 2 — Bag and label

One item per mesh bag, one plastic label per bag written in pencil or permanent marker. Pencil survives soil better than most inks. Tie each bag with a long piece of string and leave 20 cm of string above ground when you bury it. This is a simplified version of the litterbag method soil ecologists use, and the string is the part amateurs skip and regret.

Step 3 — Bury them 15 cm down, in a row

Pick a spot with real soil, not a gravel bed, somewhere that will not be dug or mown. Dig a trench 15 cm deep, space the bags 20 cm apart in a line, cover them and pat the soil down. Sketch a map with distances from two fixed landmarks, such as a fence post and a downpipe. Water the strip if the soil is dry; dry soil has almost no microbial activity.

Step 4 — Check in at days 15, 30 and 45

Do not dig anything up. Instead record soil temperature 5 cm down with a kitchen thermometer, note whether the soil is wet or dry, and water it if it has been dry for a week. Keep these notes: they are how you will explain a slow result instead of blaming the materials.

Step 5 — Dig up at day 60, dry, weigh and rank

Lift each bag by its string. Rinse the contents gently in a sieve under cold water, lay everything out on paper somewhere warm for 48 hours, then weigh again and photograph against the same ruler. Calculate percentage mass loss for each item. Rank them, then compare the ranking with the predictions you wrote down on day one.

What you should see: The banana peel is usually gone or reduced to a thin dark film, often by day 30. The cotton square comes out holed, thinned and weak enough to tear with a finger, typically losing 30 to 80 percent of its mass depending on soil temperature and moisture. The newspaper is fragile and partly consumed. The compostable plastic is the surprise: in cool soil it often comes out almost unchanged, maybe slightly cloudy and more brittle. The ordinary plastic comes out looking like you buried it yesterday. Expect the whole range from near-total loss to zero in the same trench, which is the result worth having.

What’s Actually Going On

Biodegradation is enzymatic. Soil bacteria and fungi secrete enzymes that cut specific chemical bonds, and whether a material disappears depends on whether anything in the soil owns the right scissors. Cellulose, the main component of cotton and paper, is a chain of glucose units joined by glycosidic bonds, and cellulase enzymes are everywhere in soil because plant litter has been the main food source on land for hundreds of millions of years. Starch is easier still. Fruit tissue is sugar, water and pectin, and it goes fastest of all.

Polyethylene, polypropylene and PET are different in kind, not just in degree. Their backbones are long runs of carbon-carbon bonds with no hydrolysable linkages, and no enzyme in common soil has evolved to attack them, because until about seventy years ago nothing like them existed. Degradation of these plastics in the environment happens mostly through abiotic routes — ultraviolet light, oxidation and mechanical abrasion — which fragment the material long before anything mineralises it. Chamas and colleagues, surveying degradation rates across plastic types, open by noting that plastic waste is generated at a rate approaching 400 million tonnes a year while our understanding of its persistence remains poor. Buried 15 cm down, your carrier bag gets no UV at all.

So why does the compostable bag fail too? Because “compostable” is a certification against industrial conditions, not a promise about your garden. Industrial composting runs hot: the EPA puts a well-managed pile at 131 to 160 °F, 55 to 71 °C, and it is that sustained heat plus high moisture and a dense microbial population that hydrolyses polylactic acid and starch blends. A flower bed at 14 °C does not supply any of it. The material is not mislabelled, but the label means something narrower than most people read into it. That gap — between a technically accurate claim and the inference a shopper draws — is the most useful thing in this experiment, and it is why the FTC wrote a rule about the word in the first place.

How to Explain It to Your Kid

Ages 5–8: Who can eat it?

Frame the soil as a kitchen full of very small creatures who can eat some things and not others. Leaves, fruit and cloth are on the menu. Plastic is not, because nobody down there knows how to chew it. Ask them to guess which bag will be emptiest, then draw their five guesses in order before you bury anything. Digging the samples up two months later turns into opening presents, which is the best version of waiting that a six-year-old gets.

Ages 9–12: Percentage loss is the real answer

Introduce biodegradable as a word that needs a question attached: biodegradable where, and in how long? Have them compute percentage mass loss for each sample, which is (start − end) ÷ start × 100, then build a bar chart. The comparison that does the work is the compostable plastic against the cotton. Same word on the packaging in most people’s heads; wildly different numbers on the chart.

Ages 13+: Bonds, not vibes

Give them the chemistry. Cellulose and starch are joined by glycosidic bonds that hydrolase enzymes cleave; polyethylene is a carbon-carbon chain with nothing for a hydrolase to grip. Then ask the harder question: what would a soil microbe need in order to evolve the ability? The PETase enzymes described in the last decade are a real answer and a good rabbit hole. The extension that makes this a proper investigation is to run the same five materials in two environments at once, buried and in a warm compost heap, and compare.

The question to ask: “The plastic bag came out of the ground looking new. If we had left the same bag on the roof in the sun for two months instead, would it have come out the same, better, or worse?”

Why Teaching This Early Pays Off

This experiment attacks a specific and widespread wrong model: that biodegradability is a property an object either has or lacks, like being red. It is not. It is a relationship between a material, an environment, a timescale and a community of organisms, and the same bag is biodegradable in one place and inert in another. Smith, diSessa and Roschelle argued that children’s misconceptions are usually productive fragments of real reasoning rather than errors to be erased, and this one is a good example: “some things rot and some don’t” is true enough to survive, and precise enough to mislead.

The payoff shows up later in several places at once. School chemistry treats polymers and functional groups abstractly; a kid who has weighed a cotton square before and after has somewhere to put that. Recycling labels, carbon footprints and the whole genre of environmental marketing claims become readable rather than intimidating. The National Research Council’s K-12 framework lists “obtaining, evaluating and communicating information” as a core science practice, and comparing a package claim with your own measurement is that practice in its purest form.

Keep the claim modest. One trench does not build environmental literacy. It does give a child a concrete reason to ask “under what conditions?” when somebody uses a comforting word, and that habit is worth more than the data.

A Biodegradation Experiment Kids Can Run Safely: What Parents Should Know

Best age	7 to 14. Below 7, sixty days is an eternity, though a younger sibling can help dig up
Supervision	An adult picks the dig site and handles the trowel in unfamiliar soil. Gloves for everyone, and hands washed with soap afterwards
Real hazards	Buried glass, nails and wire in older gardens; animal faeces in soil, which can carry toxoplasma and roundworm, so gloves and no hand-to-mouth contact; tetanus risk from a puncture wound, so keep vaccinations current
Don’t	Do not bury batteries, medicines, electronics, meat, fish or dairy. Batteries leach metals, and animal products attract scavengers who will excavate your experiment. Do not dig on land that is not yours, and do not dig deeper than 30 cm anywhere near a buried cable or pipe

When It Doesn’t Work

• You cannot find the samples. The commonest failure by a wide margin. Mesh bags, long strings left above ground, plastic labels, and a sketched map with two measured distances. Do all four; any one of them alone fails.
• Nothing decomposed at all, including the cotton. Usually dry soil or cold soil. Below roughly 10 °C microbial activity falls off sharply, and bone-dry soil is nearly inert. Check your temperature and moisture notes before concluding anything about the materials.
• A sample has vanished entirely. Worms and beetles can drag soft material out through coarse mesh, and a fruit sample can genuinely disappear. Record it as near-total loss, not as missing data, and use finer mesh next time.
• The labels are illegible. Water-based ink dissolves, and paper labels pulp. Pencil on plastic plant markers survives sixty days in wet soil. Photograph the labelled bags before burying them as a backup.
• The compostable item looks unchanged and your child calls it a scam. It is not a scam, it is a certification against industrial composting conditions. This is the conversation the experiment exists to start, not a result to be embarrassed about.

Take It Further

• Two environments, same five materials. Bury one set and put an identical set in a warm compost heap or a wormery. The variable is the environment, not the material, and the difference in the compostable plastic’s fate is often dramatic. Pair it with our compost jar experiment to see the microbial side up close.
• Sun versus soil. Tape identical plastic squares to a south-facing wall and bury their twins. After sixty days, test both by stretching them until they tear. UV embrittles the exposed one noticeably while the buried one is unchanged, which separates photodegradation from biodegradation.
• Depth as the variable. Bury cotton squares at 5, 15 and 30 cm. Oxygen, temperature and microbial density all fall with depth, and the mass-loss curve shows it. Measure soil temperature at each depth to make the explanation yours rather than borrowed.

What to Watch For Over the Next 3 Months

• Week 4 after the dig-up: They read a package label out loud in a shop and ask “biodegradable where?” That one question is the whole return on sixty days of waiting.
• Month 2: The vocabulary appears sideways: asking why a landfill does not just compost itself, or why a wooden spoon in the garden lasts years while a cotton rag does not. Both are good questions with real answers.
• Month 3: The follow-up worth encouraging is about materials design: could someone make a plastic that microbes can eat? They can, and do, and the trade-offs between durability and degradability are a genuine engineering problem. A good next build is making bioplastic from cornstarch and glycerin, followed by burying a piece of it.

Frequently Asked Questions

Is sixty days long enough to see anything?

Yes for fruit, cotton and paper, which change visibly within weeks in warm moist soil. No for conventional plastic, and usually no for compostable plastic in a cool garden. That uneven result is what makes the comparison informative rather than a foregone conclusion.

Can we just bury things without bags?

You can, but you will lose the small and soft samples and you will not be able to weigh what is left. The mesh bag is what turns a burial into a measurement, and it is the same reason soil ecologists use litterbags.

Does it matter where in the garden we dig?

It matters a lot. Compost-rich bed soil has a far larger microbial population than compacted clay or gravel. Pick one spot for all five samples so the environment is a constant, and record what kind of soil it is.

Should we wash the soil off before weighing?

Yes, gently, in a sieve under cold running water, then dry everything for 48 hours in the same conditions. Adhering soil can easily outweigh what remains of a decomposed sample and will quietly ruin your numbers.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. U.S. Federal Trade Commission. (2012). “FTC Issues Revised ‘Green Guides’.” https://www.ftc.gov/news-events/news/press-releases/2012/10/ftc-issues-revised-green-guides
2. Chamas, A., Moon, H., Zheng, J., Qiu, Y., Tabassum, T., Jang, J. H., et al. (2020). “Degradation Rates of Plastics in the Environment.” ACS Sustainable Chemistry & Engineering, 8(9), 3494-3511. https://doi.org/10.1021/acssuschemeng.9b06635
3. U.S. Environmental Protection Agency. “Types of Composting and Understanding the Process.” https://www.epa.gov/sustainable-management-food/types-composting-and-understanding-process
4. Penn State Extension. “Soil Quality Information.” https://extension.psu.edu/soil-quality-information
5. Smith, J. P., diSessa, A. A., & Roschelle, J. (1994). “Misconceptions Reconceived: A Constructivist Analysis of Knowledge in Transition.” Journal of the Learning Sciences, 3(2), 115-163. https://doi.org/10.1207/s15327809jls0302_1
6. National Research Council. (2012). A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. National Academies Press. https://doi.org/10.17226/13165