How to Make Compost at Home: 4-Week Hot Method vs 6-Month Cold Method — Which Suits Your Garden
Learn how to make compost at home — greens vs browns explained, hot vs cold methods, bin types compared, troubleshooting, and how to use the finished product.
UK households throw away around 6 million tonnes of food and drink every year — and according to WRAP’s 2025 Key Facts report, only about 17% is currently composted or sent for anaerobic digestion. [4] The rest goes to incineration or landfill. Compare that to Wales, where 45% of food waste is already diverted — proof of what’s possible when home composting becomes the default rather than the exception.
Good compost is worth the effort. Finished compost improves soil structure, feeds earthworms and beneficial microbes, helps sandy soils retain moisture, breaks up heavy clay, and delivers a slow release of balanced nutrients — all for free, made entirely from material you’d otherwise bin. When I started composting in a clay-heavy back garden, the difference after a single season was striking: the beds I dug compost into were markedly easier to work, and drainage improved noticeably through the following winter.
This guide covers everything a first-time composter needs to know — the two types of materials and why the balance matters, which method suits your situation, an honest comparison of bin types, what to put in and what to leave out, step-by-step setup, troubleshooting fixes, and a clear explanation of how to use the finished product effectively.
Greens and Browns: The Two Ingredients You Need
Every composting guide talks about greens and browns, but understanding the chemistry behind them is what separates a heap that works from one that stalls after a few weeks.
Seasonal Garden Calendar
Know exactly what to plant, prune and sow — every month of the year.
Greens are nitrogen-rich materials. Nitrogen fuels the bacteria and fungi responsible for decomposition. Without enough nitrogen, the microbial population stays small and the heap barely moves. Common greens include:
- Fresh grass clippings
- Vegetable peelings, fruit scraps, and kitchen prep waste
- Coffee grounds (up to 2% nitrogen by volume [8]) and tea leaves
- Annual weeds without seed heads
- Fresh plant trimmings and soft stems
- Nettles and comfrey leaves — both nitrogen-rich and effective as natural activators
Browns are carbon-rich materials. Carbon provides energy and, crucially, physical structure. It creates air pockets that keep the heap aerobic — a heap without browns quickly turns anaerobic, producing the distinctive rotten-egg smell that puts many people off composting entirely. Common browns include:
- Corrugated cardboard and cardboard packaging (remove tape)
- Cereal boxes and standard food packaging — Garden Organic confirms that vegetable-based inks are now standard on most printed cardboard and are safe to compost [2]
- Dry autumn leaves
- Straw and hay
- Shredded paper and newspaper
- Woody prunings (chipped or shredded)
- Egg cartons and egg boxes
Getting the Ratio Right
The target is roughly equal volumes of greens and browns, according to Garden Organic [2] — though the RHS recommends a slightly wider range: 25–50% greens to 50–75% browns. [1] In practice, most beginners accumulate too many greens (kitchen waste builds up quickly) and not enough browns. The simplest fix is keeping a supply of torn cardboard next to the bin so you can add it every time you put in kitchen scraps.
You might also find choose perfect first helpful here.
One specific warning from the RHS: grass clippings added alone will turn into “a slimy, smelly mess” quickly. [1] Always mix them with torn cardboard or dry leaves first — a thin layer of grass, then a layer of browns, then more grass. The same principle applies to any high-moisture green material.
Hot vs Cold Composting: Which Method Suits You?
These aren’t fundamentally different processes — they’re the same microbial decomposition running at different speeds and temperatures. Your choice depends on how much effort you want to invest and how quickly you need finished compost.
Cold Composting
Cold composting is what most home composters actually do. You add materials gradually as they accumulate — kitchen waste one day, some cardboard the next, grass clippings after mowing. The heap builds slowly, temperatures stay moderate, and decomposition happens without much intervention.
- Timeline: 6 months to 2 years, depending on material size, ratio, and season
- Effort: Very low — add materials, occasionally turn, wait
- Drawback: Does not reliably reach temperatures high enough to kill weed seeds or plant pathogens
- Best for: Most home gardeners; consistent year-round composting of kitchen and garden waste
Hot Composting
Hot composting means deliberately engineering conditions for rapid thermophilic (heat-loving) decomposition. An active heap generates significant internal heat — up to 70°C in a well-managed pile [3] — which dramatically speeds breakdown and kills most weed seeds and pathogens.
- Timeline: 6–8 weeks with sustained effort [2]
- Effort: High — fill the container completely in one go, chop materials small, turn regularly
- Pathogen destruction: Most plant pathogens are eliminated if the heap sustains 54–60°C for 72 hours, according to Cornell Composting’s research [7]
One detail that most beginner guides miss: if your heap climbs above 71°C (160°F), it can begin to self-sterilise — killing the beneficial microbes doing the actual decomposition work, stalling the whole process. [7] The fix is immediate: turn the heap to cool the core and reintroduce oxygen. Temperature recovers within 2–3 hours of turning. If you’re hot composting seriously, a compost thermometer is a worthwhile investment. The smarter approach is temperature-triggered turning — turn when the core drops below 55°C or rises above 70°C — rather than a fixed weekly schedule.
Compost Bin Types: An Honest Comparison
There’s no single best option. The right choice depends on your space, budget, and what you need to compost.
| Type | Cost | Speed | Best For | Key Limitation |
|---|---|---|---|---|
| Open heap | Free | Slow (1–2 years) | Garden waste, large volumes, prunings | Needs covering; can attract vermin if food scraps added uncovered |
| Closed plastic bin | Free–£30 (council subsidies common) | Moderate (6–12 months) | Mixed kitchen and garden waste; most common starter option | Access to finished compost at the base can be awkward |
| Tumbler | £50–£150 | Fast (4–8 weeks) | Kitchen waste; tidy appearance; faster results | Limited capacity; not suited to bulky garden waste |
| Wormery (vermicomposting) | £50–£100 | Moderate (3–6 months) | Kitchen scraps; flats and small gardens; patio use | Worms need management in extreme cold or heat; no large volumes |
| Bokashi system | £30–£100 + ~£25/year bran | 2 weeks fermentation + 4 weeks burial | All food waste including meat, fish, dairy, cooked food | Output is pre-compost — must be buried or added to a heap to finish |
Bokashi: The Exception to the Rules
Bokashi deserves special attention because it works on an entirely different principle. It’s an anaerobic fermentation system — not composting — that uses bran inoculated with beneficial microorganisms to ferment food waste in a sealed container. Its defining advantage is that it accepts cooked food, meat, fish, and dairy, which you can’t safely add to any open or standard closed bin.
The catch: the output is not finished compost. According to the RHS, the fermented material is still acidic and needs to be buried at least 30cm deep, with two to four weeks before planting in the same area. [5] GrowVeg recommends a two-bin system so one container can ferment while the other fills — essential for continuous use. [6] The liquid produced (“Bokashi tea”) should be diluted 1:100 for applying to soil. Budget around £50–£100 for a two-bin starter kit plus roughly £25 per year for bran.
What to Compost — and What to Leave Out
Safe to Add
Beyond the greens and browns listed above, most kitchen and garden waste composts well:
See also our guide to start garden from scratch: beginner’s.
- Fruit and vegetable peelings, including citrus
- Tea bags (paper-based) and loose tea leaves
- Coffee grounds and paper filters
- Crushed eggshells (break down slowly but add calcium)
- Fallen leaves — shred them to speed decomposition significantly
- Hair (human or pet), nail clippings, and untreated wool
- Old potting compost that wasn’t used for diseased plants
- Wood ash in small quantities (adds potassium; raises pH slightly)
Leave These Out of a Standard Heap
- Meat, fish, and dairy — not harmful to the compost itself, but will attract rats and foxes in any open or standard closed bin. Bokashi only.
- Diseased plant material — cold composting doesn’t reliably hit temperatures high enough to kill pathogens or fungal spores. Bag it and put it in the council bin, or place it in the hot core of a well-managed hot heap.
- Perennial weed roots — bindweed, couch grass, and ground elder roots survive cold composting and regrow. If you want to compost them, drown them in a covered bucket of water for several weeks until they’re fully dead before adding.
- Cat and dog waste — carries pathogens including Toxoplasma gondii not safely destroyed at cold composting temperatures.
- Coal ash and coke ash — contains plant-harmful compounds. Wood ash in small quantities is fine.
- Anything treated with pesticides or herbicides — slug pellets and insecticides kill beneficial organisms in the heap. [3]
- Fire-retardant or specialist cardboard — contains pollutants. Standard food packaging and cereal boxes with vegetable-based inks are perfectly safe. [2]
One widely repeated myth worth correcting: you do not need to add lime. The RHS is explicit that lime “provides no benefit” and is unnecessary when the green/brown balance is correct. [1] Save the money.
How to Start Your Compost Heap
Choosing the Right Spot
Site your bin in a sheltered position in partial or full shade, positioned directly on bare earth if possible. The RHS recommends this approach because earth contact lets worms migrate up into the heap naturally and supports drainage — both important for an active, healthy pile. [1] Avoid full sun, which dries the heap too quickly in summer.
Size Matters More Than You’d Expect
This is one of the most consistently overlooked points in beginner guides: volume drives temperature, and temperature drives speed. The RHS recommends a minimum of approximately 1 cubic metre (1m × 1m × 1m) for efficient decomposition. [1] Smaller heaps simply struggle to generate and retain enough warmth for active microbial work. The standard council-provided plastic bin holds around 220 litres — about one-fifth of that volume — which is why council bins produce compost slowly. They work, but expect cold-composting timescales.
Building the Heap Step by Step
- Base layer: Lay a few woody branches or stems on the bare earth first. This creates air channels at the bottom and supports drainage throughout the heap. [3]
- Alternate greens and browns: Build up in alternating layers — roughly equal by volume. No single layer should be deeper than about 10–15cm before being balanced with the opposite material type.
- Moisten as you go: The heap should feel like a wrung-out sponge — damp throughout but not dripping. If your greens are fresh and wet, the browns will absorb much of the moisture. In dry weather, water each layer lightly as you build.
- Cover the top: An old piece of cardboard, a sheet of polythene, or a proper lid retains moisture in dry spells and prevents waterlogging in heavy rain. Garden Organic notes a bin isn’t even strictly necessary — a covered heap on bare earth works just as well. [3]
For hot composting, the approach is different: fill the bin completely in a single session rather than adding gradually; chop all materials into pieces no longer than 5–10cm; mix greens and browns together before adding rather than layering; and water thoroughly as you fill. [2]
Do You Need a Compost Activator?
Walk into any garden centre and you’ll find commercial activators promising faster results. The honest verdict: a 2008 Which? investigation found no significant benefit from proprietary activators when the green/brown ratio was already balanced. [8] The RHS agrees — activators are unnecessary when materials are correctly proportioned. [1]
For more on this, see make christmas wreath.
If your heap is genuinely sluggish, the best free alternatives are things you likely already have:
- Comfrey leaves — nitrogen-rich, widely available in UK gardens, and one of the most effective natural activators
- Fresh nettles — equally nitrogen-rich and free from most hedgerows
- A spadeful of finished compost — introduces exactly the right microbial community to kick-start a new heap
- Diluted urine (1 part to 10 parts water) — rarely mentioned in mainstream guides but genuinely effective on a dry or slow cold heap, and completely free
Troubleshooting: Fixes for Common Problems
Most composting problems have a straightforward cause and a quick fix once you know what to look for.
| Problem | Likely Cause | Fix |
|---|---|---|
| Wet, slimy, smells of ammonia or rotting | Too many greens; insufficient browns; poor aeration | Add torn cardboard, straw, or wood chip; turn to introduce air; cover the top [1] |
| Rotten-egg smell (sulphurous) | Anaerobic conditions — oxygen-deprived heap | Turn thoroughly; add browns to open the structure; check the base has air gaps [3] |
| Dry, fibrous, barely decomposing | Too many browns; not enough greens; too dry | Add fresh greens; water thoroughly; mix in grass clippings or nettles [1] |
| Ants nesting in the heap | Heap is too dry — ants only colonise dry material | Water the heap well; turn to moisten and disturb the core [3] |
| Decomposing too slowly | Materials too large; wrong ratio; heap too small; cold weather | Chop or shred materials smaller; correct the green/brown balance; add a natural activator in spring |
| Flies around the bin | Exposed fresh kitchen waste on the surface | Always cover kitchen scraps with a layer of garden material or torn cardboard; bury scraps into the heap centre [1] |
The ants point from Garden Organic is one I find genuinely useful — most beginners see ants in the heap and assume it’s a pest problem. It’s not: it’s a diagnostic signal that the heap is too dry and needs water and turning attention. [3]
Related: make wildlife garden: attracting birds.
How to Know When Your Compost Is Ready
Finished compost is dark brown, crumbly, and smells like damp woodland — not remotely like rotting food. [1] It has a loose, friable texture and you shouldn’t be able to identify individual ingredients. Some woody fragments may still be present; these can simply go back into the new heap.
Timeline expectations by method:
- Hot composting: 2–3 months with regular turning and correct materials
- Cold composting (standard bin): 6–12 months
- Open heap: 12 months to 2 years
- Tumbler: 4–8 weeks when used correctly with a balanced mix
- Wormery: 3–6 months for the first castings harvest
Garden Organic recommends allowing a further 1–2 months of maturation after the heap appears finished. [2] Partially broken-down compost contains elevated concentrations of organic acids that can inhibit germination — particularly a problem if you’re planning to use it around seedlings. When in doubt, let it rest a little longer.
How to Use Finished Compost
Soil Improver
This is the primary use for most gardeners. Dig 5–10cm of compost into planting beds in autumn or spring, working it into the top 20–30cm of soil. It improves structure on both extremes: heavy clay becomes more workable and drains better; sandy soil retains moisture and nutrients for longer. This is also the most effective way to enrich the soil in raised beds and productive containers at the start of each growing season.
Surface Mulch
Spread compost at least 5cm thick over bare soil around established plants in late winter or early spring. The RHS recommends this for suppressing weeds, retaining moisture through summer, and feeding the soil without digging. [1] Earthworms pull it down naturally over the following weeks. Pull mulch a few centimetres back from plant crowns and stems to avoid creating conditions for rot.
Potting Mix Ingredient
Homemade compost can be used as one component in a potting mix, but should never be used neat in containers — it’s too nutrient-dense and often too moisture-retentive on its own. A reliable starting ratio is 1 part compost : 1 part sharp grit or perlite : 1 part topsoil or multipurpose compost. This dilutes the intensity, improves drainage, and creates a balanced growing medium.
Important for seedlings: do not use neat homemade compost in seed trays or plug trays. The concentrated nutrient levels can inhibit germination and scorch tender roots. Use a purpose-made seed compost instead, or limit homemade compost to no more than 20% of a seed tray mix.
Compost Tea
Compost tea is water steeped with finished compost to extract beneficial microorganisms — bacteria, fungi, protozoa, and nematodes — for use as a liquid inoculant and plant feed. The actively aerated version (AACT) uses an aquarium pump running for 24–36 hours, with a tablespoon of unsulphured molasses added to feed the microbes as they multiply. Apply immediately after brewing — beneficial populations crash once aeration stops, and beyond 36 hours there is a real risk of pathogenic bacteria including E. coli and Salmonella proliferating. Use rainwater or tap water left overnight (chlorine off-gasses naturally): chlorinated water kills the microbes you’re cultivating. Apply as a soil drench or foliar spray in the morning, before direct sun reaches the leaves — UV light degrades the microbial populations within hours.
Try our free Raised Bed Soil Calculator to get personalized results for your garden.
Build your perfect mix with our Compost Recipe Builder to get personalized results for your garden.
Frequently Asked Questions
Can I compost in winter?
Yes — decomposition slows significantly below 10°C and effectively pauses below 4°C, but the heap doesn’t die. It stores materials through winter and returns to activity as temperatures rise in late February and March. Keep adding material through winter, and insulate the bin with a piece of cardboard or old carpet on top in sustained cold spells.
How often should I turn my compost?
For cold composting: every four to six weeks is adequate. For hot composting: use the temperature-triggered method — turn when the core drops below 55°C or rises above 70°C, rather than on a fixed schedule. [2] Turning more frequently than necessary in a cold heap provides minimal benefit; the most common mistake is not turning enough.
Do I need a compost bin, or will a heap work?
A bin is not essential. Garden Organic explicitly notes that a heap covered with a sheet of polythene or cardboard works just as well. [3] The covering is what matters — it retains moisture in dry weather and prevents waterlogging in wet weather. A bin primarily keeps things tidy, helps retain warmth, and reduces vermin access if you’re adding kitchen scraps.
Can I compost pet hair, human hair, and nail clippings?
Yes — human and pet hair and nail clippings are nitrogen-rich and fully compostable. They decompose slowly and tend to mat, so mix them well with browns before adding rather than adding in clumps. Dog and cat faeces should not be composted in a standard heap — only the hair.
How do I know if my heap is actually working?
Three reliable signs: (1) the volume reduces noticeably over weeks as material breaks down; (2) there’s warmth in the core — an active cold heap typically runs at 20–30°C, a hot heap at 45–70°C; (3) you find worms when you dig into the lower layers. No warmth, no volume reduction, and no worms after several months points clearly to a green/brown balance or moisture problem.
What’s the difference between compost and mulch?
Compost is a finished organic material spread for its nutritional and structural benefits. Mulch describes the practice of covering soil with any material — compost, wood chips, leaf mould, or straw — to suppress weeds and retain moisture. Compost can be used as a mulch, but not all mulches are compost. When you spread a 5cm layer of finished compost over a border in spring, you’re doing both at once.
Key Takeaways
- Aim for roughly equal volumes of greens and browns — keep torn cardboard ready to add alongside every batch of kitchen scraps
- Grass clippings alone create a slimy, smelly mess — always mix with browns first
- Hot composting (2–3 months) requires filling all at once and regular turning; cold composting (6–12 months) suits most home gardeners with minimal effort
- Volume matters: below roughly 1 cubic metre, decomposition slows considerably [1]
- Meat, dairy, diseased plants, perennial weed roots, and pet waste all stay out of standard heaps
- Ants in the heap means it’s too dry — water and turn it
- Commercial activators show no benefit when greens and browns are balanced — comfrey, nettles, or finished compost work better and cost nothing
- Finished compost smells like damp woodland; it’s dark brown and crumbly
- Never use neat homemade compost for seedlings — dilute with grit and multipurpose compost
Sources
- [1] RHS. “Composting.” Royal Horticultural Society. rhs.org.uk
- [2] Garden Organic. “How to Make Compost.” gardenorganic.org.uk
- [3] Garden Organic. “Composting Overview.” gardenorganic.org.uk
- [4] WRAP. “UK Food Waste & Food Surplus — Key Facts.” July 2025. wrap.ngo
- [5] RHS. “Bokashi: How to Recycle Food Waste.” rhs.org.uk
- [6] GrowVeg. “Bokashi Composting: Cooked Food Waste for Your Garden.” growveg.co.uk
- [7] Cornell Composting. “Compost Physics — Factsheet 5.” Cornell University. compost.css.cornell.edu
- [8] Carry on Composting. “Compost Activators and Accelerators.” carryoncomposting.com
