How to make compost at home in 5 steps: a complete guide

Home compost turns kitchen and garden scraps into the best fertiliser you can add to your soil — a complete, balanced organic amendment full of soil life — and it does it for free. Along the way, it halves the organic waste you take out of the house and avoids the methane that waste would generate in landfill. You don't need anything sophisticated or any paid activator: a corner, a simple composter and understanding a single rule, the balance between "green" and "brown" materials.

This guide has the complete process in five steps: choosing the system and the site; the green/brown rule with lists of what to and what not to; how to build the pile in layers; how to aerate it and control moisture; and how to know when it's ready and what to use it for. Plus a troubleshooting table (odours, flies, ants, rodents), how to make leaf mould separately, and the frequently asked questions.

Step 1. Choose the system and the site

The system

• Closed plastic composter (300-600 L): the most practical for a private garden. It keeps in heat and moisture, keeps out rodents, contains odours and looks tidy. With a lid on top to add and a hatch at the bottom to take out the finished compost. Most councils sell them subsidised or give them away.
• Pallet or wooden bay (2-3 compartments): for people with plenty of space and plenty of garden material. It lets you have one "under construction" pile, another "maturing" and finished compost, and turn from one compartment to another to aerate.
• Tumbler composter (drum): aerated by turning a handle, with no need for a fork. Fast and clean, and raised off the ground (rodent-proof), but low capacity and more expensive.
• Wormery (worms): the indoor version for flats and balconies. Red wriggler worms (Eisenia) process kitchen scraps and produce very high-quality castings and a leachate ("tea") that is diluted for watering. It doesn't smell if used properly and not overloaded.
• Trench or "in situ" composting: burying kitchen scraps directly in a furrow in the veg garden between rows of crops. Zero infrastructure, but only good for small amounts.

The site

Place the composter directly on soil (so the worms and soil microfauna can come up), in part shade (in full sun it dries out constantly, in full shade it goes very slowly and cold), with easy access from the kitchen so you have no excuse, and near a water source to wet it when needed. Leave room around it so you can turn it with the fork.

Step 2. The green/brown rule

Aim for a rough ratio of 2 or 3 parts brown to every 1 of green by volume (not by weight). If in doubt, add more brown: an excess of green is what makes the pile cake, run out of oxygen, rot and smell bad. Always keep a store of brown material (a bag of dry leaves or shredded cardboard) next to the composter to cover each kitchen addition.

Never add: meat, fish, bones, dairy, oil and fat, cooked scraps with salt or sauce, bread in quantity, dog or cat faeces (pathogens), nappies, coal ash, very diseased plants, or weeds with mature seeds or with rhizome (couch grass, bindweed, nutsedge). They attract rats, generate bad odours or spread problems to the garden when you use the compost.

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Step 3. Build the pile in layers

1. Start with a layer of twigs or coarse prunings at the bottom (10-15 cm) so air can circulate underneath and drain off excess water.
2. Alternate a thin layer of greens (5-8 cm) with a double layer of browns.
3. Chop up everything you can before adding it: the smaller it is, the more surface for the microorganisms and the faster the process. A whole branch takes a year; the same branch shredded, a few weeks.
4. Every time you add kitchen scraps, cover them with a good handful of brown material or soil. That's the trick that avoids fruit flies, bad odours and rodents.
5. Every now and then add a handful of finished compost, garden soil or manure: it seeds the pile with microorganisms and works as a natural activator, for free.

You can build the pile all at once (if you have plenty of material at the same time, such as after a big prune) or add to it bit by bit (the normal thing at home). The all-at-once one heats up more and goes faster ("hot" compost); the continuous-addition one is more convenient and gives "cold" compost that takes longer but works just as well.

Step 4. Aerate and control moisture

Compost needs two things to break down well and not rot: oxygen and a moisture level like a well-wrung-out sponge.

• Aeration: every 1-2 weeks, turn it with a fork or a key aerator to get air in and mix the edge (cold, not very active) with the centre (hot). If you have a pallet bay, turn all the material from one compartment into the next.
• Moisture: squeeze a handful of the material. If water drips out, there is too much moisture: add dry brown and aerate thoroughly. If it crumbles to powder and won't form a ball, it's too dry: water lightly with the watering can and turn it.

A well-balanced pile heats up to 40-65 °C in the first few days (put your hand in or stick a pole in for a few minutes: it should feel clearly hot in the centre). That heat is the sign that aerobic decomposition is going well, and it also destroys weed seeds, larvae and pathogens. When it stops heating up after turning, the active phase is over and maturation begins, slower and at room temperature.

Step 5. Harvest and use the compost

In 3-6 months (more in winter, more if you don't aerate, less if you chop well and turn often) you'll have mature compost. You recognise it like this:

• Dark brown, almost black colour.
• Smells of woodland soil, pleasant, with no trace of rot or ammonia.
• Crumbly texture, spongy, not compact.
• No recognisable remains (the odd twig, an avocado stone or a nut shell is normal; they go into the next batch).

Take it out through the bottom hatch or remove the unfinished top part (which goes back into the pile), sieve the coarser bits with a 1-1.5 cm mesh, and use it:

• Nutritious mulch: 2-4 cm over the surface of beds and under trees and shrubs, once or twice a year (spring and autumn). Don't dig it in: let the worms incorporate it.
• Planting mix: in equal parts with the soil from the hole of each new plant.
• Potting mix: 20-30% well-matured, sieved compost, mixed with universal growing medium and perlite.
• Compost tea: one part compost to ten of water, steep for 24-48 h while stirring, strain and water demanding plants with it or spray the leaves (it supplies beneficial microorganisms).
• Seedlings: only very mature compost, finely sieved and mixed with sand or vermiculite; young or "hot" compost scorches seedlings.

Troubleshooting

Leaf compost (leaf mould) separately

Autumn leaves break down slowly and mostly with fungi, not bacteria, so they don't do well in large amounts in the normal composter (they cool it, cake it and slow everything down). It's best to make leaf mould separately: pile the leaves in a corner, in a wire cage or in black bin bags with a few holes, water if they're dry, and leave them one or two years untouched. You'll get a dark, spongy mulch, excellent for acid-lovers, for seedlings and for improving soil structure. Chopping the leaves by running the mower over them speeds up the process a lot.

Hot compost versus cold compost

For home use, cold compost is the practical one. Save the hot method for when you want to "sterilise" scraps with weed seeds or for a large one-off amount.

Wormery leachate and "compost tea"

The leachate is the dark liquid that drips from the bottom of a wormery. Collect it, dilute it 1:10 (one part leachate, ten of water) until it's the colour of weak tea, and water with it. It's a mild liquid fertiliser; undiluted it can be too concentrated and sometimes contains poorly aerated compounds.

Compost tea is prepared separately: put mature compost in a stocking or a mesh bag, submerge it in a bucket of chlorine-free water (let tap water stand for 24 h), stir or bubble with an aquarium aerator for 24-48 h, and water or spray straight away. It supplies beneficial microorganisms that colonise the leaf and the rhizosphere. Use it the same day, don't store it.

What to do with the compost by season

• Autumn: the best time to spread compost as mulch over the whole garden. The rains and worms incorporate it over winter and by spring the soil is ready.
• Spring: compost under fruit trees and in the hole of new plantings; compost tea to get the veg garden going.
• Summer: a thin layer around the most demanding plants, as a nutritious mulch that also keeps in moisture.
• Any time: as a component of potting and seedling mix (always well matured and sieved).

Frequently asked questions

Can I compost in winter?

Yes, although the process slows down a lot in the cold (the microorganisms work less and the pile doesn't heat up). Keep adding scraps as normal; in spring, with the warmth, it restarts on its own. A closed, well-filled composter holds its internal heat better over winter.

Can you compost kitchen paper and used napkins?

Yes, if they only have food remains or light vegetable grease. They count as brown material. Don't compost paper with a lot of coloured ink, foil, waxed paper, or napkins with meat remains or plenty of oil.

How much compost comes out of a composter?

The volume shrinks enormously during the process: from a composter filled to the top you get around a third of its capacity in finished compost. The rest leaves as water vapour and CO₂ during decomposition.

Can I add citrus and onion peel?

In small amounts, yes. In excess they acidify the pile and worms reject them. Chop them and spread them among other materials. If you compost with worms (wormery), limit citrus, onion, garlic and spice a lot.

Do I need a bought compost activator?

No. A handful of mature compost, garden soil, manure or fresh nettles acts as a natural activator by supplying microorganisms and nitrogen. Commercial activators speed up the start a little, but they're not essential and they're expensive.

Does home-made compost have "bugs" in it? Is that bad?

A healthy compost is full of life: worms, springtails, woodlice, beetles, centipedes, fungi. That's exactly what you want, and that fauna is what breaks down the material and then enriches your soil. Don't confuse that beneficial microfauna with a pest: it won't attack your plants.

Can you compost chicken or rabbit droppings?

Yes, it's an excellent "green" very rich in nitrogen. Chicken droppings are very strong (lots of ammonia and salts): use them in small amounts and well mixed, or let them compost separately for several months before using them, because fresh they scorch roots. Rabbit droppings are milder and can be used almost straight away.

Can I compost plant remains that have had pests or fungi?

Remains with pests (aphids, whitefly) yes, no problem. Those that have had serious fungi (downy mildew, black spot, bad powdery mildew) or quarantine pests, better in the bin, unless your compost reliably reaches 55-65 °C throughout the mass, which destroys the spores.

Does compost "scorch" plants?

Only immature compost, still "hot" and with an excess of ammoniacal nitrogen, can scorch roots and seedlings. Mature compost (black colour, woodland smell, no remains) is safe for any plant and in any reasonable amount.

How long does stored compost last?

Mature compost keeps well for months in a closed or covered bag, in a cool place. Over time it loses some soluble nutrients (nitrogen) but keeps its value as a soil improver. If it dries out completely, moisten it before using it.

Can I have a composter if I have a dog?

Yes, with a closed composter. Never add the dog's faeces (pathogens such as Toxocara that aren't destroyed at household temperature), and make sure the dog doesn't dig in it if you add kitchen scraps; a closed lid and never adding meat prevent this.

That compost is the best way to improve any of the soil types and fits squarely into a sustainable garden that generates no green waste and doesn't depend on bought fertilisers.