Compost kitchen scraps at home: greens, browns, moisture and turning
Kitchen scraps can become good soil once you know the green-to-brown ratio, keep the moisture right and turn the pile for air. Plus fixes for smells and flies.
- Compost needs four things - green material, brown material, moisture and air.
- Start at roughly 2-3 parts brown to 1 part green by volume, then adjust by smell and feel.
- A bad smell almost always means too wet or too much green. Add browns and turn.
- Finished compost is dark, crumbly, smells like soil, and you can no longer tell what went in.
Vegetable scraps, fruit peel and dry leaves from around the house can turn into the dark, crumbly soil vegetables love, with almost nothing to buy. There are only four things to get right: green material, brown material, moisture and air. This is the second lesson of the path “Start a pesticide-free kitchen garden”: the ratio, how to build the pile layer by layer, how to look after it, and how to fix the usual problems.
What “greens” and “browns” mean
The microbes that break down a pile need carbon for energy and nitrogen to build cells. Composters call these browns and greens. It is not about the actual colour. It is about whether a material is fresh and moist, or dry and tough.
| Greens (high nitrogen, fresh, moist) | Browns (high carbon, dry) |
|---|---|
| vegetable scraps, fruit peel | dry leaves |
| coffee grounds, used tea leaves | straw, dry grass |
| fresh grass clippings | torn cardboard, not glossy |
| seedlings thinned from the bed | sawdust from untreated wood |
What to keep out of a home pile
- Meat, fish, bones, dairy and oily food. They smell and attract rats, dogs and flies.
- Dog and cat faeces. They can carry germs that infect people; keep them away from food beds.
- Diseased plants, and weeds that have set seed. A small pile does not get hot enough to kill them.
- Glossy paper, plastic, and bags that claim to be compostable without clear details.
The ratio: start at 2-3 to 1
A common starting point is roughly 2-3 parts brown to 1 part green, by volume. No need to measure exactly, since every material is different. Let smell and feel guide the adjustments.
Example: one household kitchen for a week
Say a household produces about 1 litre of fruit and vegetable scraps a day.
- One week of greens = 1 × 7 = 7 litres
- At 2 parts brown to 1 green = 7 × 2 = 14 litres of browns
- At 3 parts = 7 × 3 = 21 litres
So you want about 14-21 litres of dry leaves or straw a week, roughly one medium bin bag. Keep a sack of dry leaves next to the pile from the start, so there is always some ready when you tip in scraps.
Build it in layers
- A base of twigs. Line the bottom of the heap or bin with small twigs, about a hand high, so air gets in from below.
- Alternate layers. About 10 cm of browns, then a thinner layer of greens, and repeat.
- Always finish with browns. Every time you add scraps, cover them with dry leaves. It stops smells and fruit flies.
- Chop things small. Small pieces break down much faster, especially tough peel and stems.
Moisture and air
Moisture: damp like a wrung-out sponge. Grab a handful from the middle and squeeze. One or two drops is right. Water running out means too wet; no water and dry crumbs means too dry.
Air: the microbes that work fast without smelling need oxygen. Turn the pile every 1-2 weeks, moving the outside to the middle, because the middle is the hottest and fastest part.
A pile that is big enough, about one cubic metre, with a good mix, heats itself to around 55-65 °C. That heat kills weed seeds and many germs, but only if it stays hot for several days and every part gets turned into the middle. A small bin at home usually doesn’t get that hot, so it is slower, and you shouldn’t rely on it to kill germs.
When is it ready?
In Thailand’s warm, humid weather, a pile turned regularly is often ready in about 2-3 months. Left alone, it may take 6 months or more. Signs it is ready:
- dark brown to black, and crumbly
- smells like soil after rain, not sour
- you can no longer tell what went in, apart from a few tough twigs
- it no longer warms up after turning
Sieve out large unfinished pieces and put them back in a new pile. The sieved compost can go straight into potting soil.
Fixing common problems
| Symptom | Usual cause | Fix |
|---|---|---|
| Rotten or ammonia smell | too wet, or too many greens | add browns, turn |
| Dry, not breaking down, not warm | too dry, or too few greens | water until damp, add scraps |
| Fruit flies | scraps showing on top | bury scraps in the middle, cover thickly with browns |
| Lots of ants | pile too dry | add moisture |
| Fat white grubs | usually insect larvae helping break things down | leave them if the moisture is right |
Compost is not a fixed recipe. Smell it, feel it, look at it, and adjust. After two or three rounds you will get the hang of it.
Using it in the vegetable bed
- Mix into soil before planting, about a third of the mix, as in the previous lesson.
- Top-dress during the season: a thin layer around the base of plants, then mulch over it.
- Before every new planting, add compost to the bed. Soil settles over time and organic matter gets used up.
Wash your hands after handling compost, and wear gloves if you have cuts on your hands.
FAQ
Can I add orange and lime peel?
Yes, but they break down more slowly than most scraps. Chop them small and don't add a lot at once.
I have a small home with no room for a big heap. Can I still compost?
Yes. Use a plastic bin with holes drilled around it, or a lidded basket. The principles are the same, but a small pile rarely gets hot, so it breaks down more slowly and will not kill weed seeds. Stick to fruit and vegetable scraps, leaves and paper.
Can compost replace all fertiliser?
Compost loosens soil, holds water and supplies a moderate amount of plant nutrients. Mix it into soil before planting and spread it on top during the season. Hungry crops such as fruiting vegetables may need extra organic fertiliser while they set fruit.
General information, not medical advice. If you are pregnant, take regular medication, or have a liver or kidney condition, ask a doctor or pharmacist before taking herbs beyond normal food amounts.