Composting
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40 free Composting trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Composting looks like the simplest job in the garden: pile up scraps, wait, and collect dark, crumbly food for the soil. Underneath, it is a busy piece of biology and chemistry, with countless microbes and a cast of small animals doing work that farmers have relied on since ancient times. This quiz covers the basics every composter learns, such as what counts as a green or a brown, why a pile heats up and what should stay out of it. It then moves on to worm bins, unusual methods from around the world, the people who shaped modern composting and the places that now require it by law. The opening questions are pitched for beginners, families and classrooms, so children learning about recycling and soil can join in. Later ones are for keen gardeners who know their way around a heap. Every answer comes with a short explanation.
30 of 40 questions with answers and explanations. Play the quiz
Q 01Which naturalist's last scientific book, published months before his death, was a study of earthworms?
Charles Darwin
Charles Darwin called it a small book of little moment, yet it sold thousands of copies within weeks of going on sale in October 1881.
Q 02A no-dig garden bed built by stacking wet paper, compost and other layers is nicknamed after which Italian dish?
Lasagna
Lasagna gardening needs no spade: the bottom layer kills the plants already growing there and suppresses weeds while everything above rots into soil.
Q 03Which kitchen leftover does the EPA say to keep out of backyard compost because it can attract animals?
Meat and bones
Meat and bones sit on the avoid list with fish and dairy, partly because a backyard pile rarely gets hot enough to break them down fully.
Q 04Which worms, native to Europe and found on every continent except Antarctica, are the usual choice for home worm bins?
Red wigglers
Red wigglers thrive in rotting vegetation instead of deep soil, and their species name fetida, meaning foul-smelling, comes from the pungent liquid they ooze when roughly handled.
Q 05According to the EPA's rule of thumb, a healthy compost pile should feel about as damp as which of these?
A wrung-out sponge
A wrung-out sponge is the target because microbes need water to stay active, while a soggy pile loses its air pockets and starts to smell.
Q 06Earthworms in a compost bin have no lungs, so which body part must stay moist to let them breathe?
Skin
Skin does the job: gases pass straight through it into the blood, and mucus-making cells keep the surface wet enough for that to work.
Q 07Food scraps rotting without air in a landfill give off which greenhouse gas, far more potent than carbon dioxide?
Methane
Methane makes up roughly half of the gas a landfill gives off, and keeping scraps out of the dump by composting them cuts those emissions.
Q 08The liquid plant feed made by soaking finished compost in water is named after which everyday drink?
Tea
Tea is the name because the mix is left to brew, typically one part compost to between four and ten parts water, with an occasional stir.
Q 09Which common compost-heap residents are crustaceans, not insects, that lose water fast and need damp, dark places?
Woodlice
Woodlice, known in North America as pill bugs or sow bugs, chew through rotting wood and dead plants, and one desert species lives in the driest habitat any crustacean has conquered.
Q 10Large compost piles and damp haystacks share which fire hazard, caused by heat building up from microbial activity?
Spontaneous combustion
Spontaneous combustion begins with heat from bacterial fermentation, which can run away until the pile ignites; large manure heaps have caught fire the same way.
Q 11Lawn clippings and vegetable peelings, the 'greens' of a compost pile, are valued mainly for supplying which element?
Nitrogen
Nitrogen is what the microbes need to grow and multiply, while the carbon in the browns is their energy supply and the fuel for a pile's heat.
Q 12Which of these compost ingredients counts as a carbon-rich 'brown' rather than a 'green'?
Cardboard
Cardboard is a brown, yet coffee grounds are a green despite their color: the labels describe what an ingredient feeds the pile, not how it looks.
Q 13Turning a compost heap with a fork keeps the microbes working mainly by supplying more of which gas?
Oxygen
Oxygen keeps the aerobic bacteria going, which need a level above 5 percent; in a compacted, airless heap other microbes take over and the smell turns foul.
Q 21Which kitchen method, named with a Japanese word, ferments food scraps in an airtight bin using a special bran?
Bokashi
Bokashi pickles waste in lactic acid instead of rotting it, and Japanese dictionaries give the word an older meaning: the shading or gradation in woodblock prints.
Q 22Which permaculture technique plants a raised garden bed on top of a buried heap of rotting logs and branches?
Hügelkultur
Hügelkultur is German for mound culture, a term first printed in a 1962 gardening booklet; its advocates say the buried wood soaks up water and releases it to the crops above.
Q 23The larvae of which insect devour food scraps so fast that farms raise them as protein for fish, pets and livestock?
Black soldier fly
Q 14What name do gardeners give to worm droppings, the end product of a worm bin that is sold as organic fertilizer?
Castings
Castings come out of the worm holding fewer contaminants and more concentrated nutrients than the scraps that went in.
Q 15Which word, Latin for 'earth' or 'ground', names the dark, stable organic matter that compost adds to soil?
Humus
Humus is what remains once rotting is finished; scraps still breaking down are technically detritus, and fully formed it looks uniformly dark and jelly-like.
Q 16The 'spent compost' sold to gardeners is a by-product of growing which crop on composted straw and horse manure?
Mushrooms
Mushrooms exhaust the mix for commercial cropping after one cycle, yet it still holds organic matter, nutrients and living microbes, so farms sell it on.
Q 17Eggshells, which gardeners crush into compost, are made almost entirely of a compound of which mineral?
Calcium
Calcium carbonate makes up 95 to 97 percent of a chicken's eggshell, which is why shells dissolve in vinegar and could even be turned into lime.
Q 18Worms, fungi and bacteria that break down dead material all play which role in an ecosystem's food web?
Decomposers
Decomposers release the nutrients locked in dead matter back into their surroundings, which is the whole point of a compost heap.
Q 19What is the gardening term for a layer of compost, bark or straw spread over the soil surface instead of dug in?
Mulch
Mulch laid thickly in a no-dig garden is pulled down into the soil by worms, insects and microbes, so the gardener never has to turn it in.
Q 20Which ingredient of traditional potting compost is dug from bogs that rank among the planet's biggest carbon stores?
Peat
Peat holds 42 percent of all soil carbon while covering just 3 percent of the land, which is why peat-free mixes swap in bark, wood fiber or coir.
Black soldier fly larvae also leave behind frass, a granular, odorless residue of droppings and shed exoskeletons that is used as fertilizer.
Q 24Which US state was the first jurisdiction to legalize human composting, known in law as natural organic reduction?
Washington
Washington requires the finished soil to be tested for arsenic, lead, mercury and other toxins, and one provider says each person yields about 1,000 pounds of it.
Q 25Which US city was the first in the country to require every home and business to separate food scraps for composting?
San Francisco
San Francisco saw composting jump 45 percent after the rule took effect, sending nearly 600 tons of scraps, soiled paper and yard trimmings to be composted every day.
Q 26Which Asian country banned food waste from landfills in 2005 and went on to recycle about 95 percent of it?
South Korea
South Korea recycled just 2 percent of its food waste in 1995; a 2013 rule made paid biodegradable bags compulsory, and the scraps become animal feed and fertilizer.
Q 27Terra preta, the fertile dark earth made by ancient farmers in the Amazon, gets its color from which added material?
Charcoal
Charcoal from low-temperature fires stays in the ground for thousands of years, holding on to nutrients that heavy rain would otherwise wash away.
Q 28PLA, the compostable plastic used for compost bags and food packaging, is usually made from the starch of which crop?
Corn
Corn starch is the usual starting point, but the plastic only breaks down properly in hot industrial composters and can linger for decades in a home pile.
Q 29Which household material, torn into strips, is a standard bedding for worm bins, since most of its inks are non-toxic?
Newspaper
Newspaper also rescues a bin that has turned too wet: mixing in fresh, dry strips soaks up the excess moisture from juicy food scraps.
Q 30Which Australian bird hatches its eggs in a huge mound of rotting leaves, testing the heat with its beak?
Brushturkey
Brushturkey males build the mound up to 4 meters across and add or remove material to hold it at 33 to 35 °C, in effect running a compost heap as an incubator.