Composting in the UK: A Complete Beginner Guide

What Is Composting?

Composting is the controlled decomposition of organic matter by bacteria, fungi, worms and other soil life. The end product is humus, a dark brown crumbly material that looks and smells like woodland soil. Humus improves soil structure, holds moisture, and feeds plants slowly and naturally.

In nature, leaves fall to the woodland floor and rot down over years. In a compost bin, we create ideal conditions for the same process to happen in months rather than years.

What to Compost

Green materials (high in nitrogen)

• Fruit and vegetable peelings
• Tea bags (check they do not contain plastic)
• Coffee grounds
• Grass cuttings
• Soft green prunings
• Annual weeds that have not gone to seed
• Cut flowers
• Poultry and horse manure (in moderation)

Brown materials (high in carbon)

• Shredded paper and cardboard (no glossy print)
• Egg boxes
• Toilet roll inners
• Autumn leaves
• Twigs and prunings (shredded)
• Straw and hay
• Sawdust and wood shavings (from untreated wood)
• Cotton and wool (in small amounts)

What NOT to compost

• Cooked food (attracts rats)
• Meat, fish and bones
• Dairy products
• Cat and dog faeces (risk of parasites)
• Diseased plant material
• Perennial weed roots like bindweed and couch grass
• Plastic, glass and metal
• Coal ash (contains toxins)
• Glossy magazine paper
• Treated wood and sawdust

Diseased plant material and perennial weed roots should be burned or put in the council bin, not composted. The average home compost heap does not get hot enough to kill them. See our guide to preventing weeds in garden beds for dealing with perennials.

Choosing a Compost Bin

Plastic Dalek bins

The classic UK compost bin is a black plastic cone about a metre tall. They cost 30 to 60 pounds, or are sometimes available free or cheap from local council recycling schemes. They are small, neat, and keep heat in well. The downside is the small opening makes turning the compost difficult.

Wooden bin boxes

Wooden bins made from slatted timber look better and are easier to manage because you can remove the front slats to get to the compost. They cost 80 to 200 pounds for a single bay, or 200 to 500 pounds for a 3 bay system. Timber bins blend into the garden better than plastic.

Hot composters

Insulated hot composters like the Hotbin reach temperatures of 40 to 60 Celsius, hot enough to break down cooked food, meat and weeds. They produce compost in 30 to 90 days rather than 12 months. They cost 200 to 350 pounds but they are a serious piece of kit for serious composters.

Tumblers

Compost tumblers are rotating drums on a stand. You turn the drum every few days to mix the compost. They are good for small gardens and produce compost quickly, but they are expensive (100 to 300 pounds) and have limited capacity.

Open heaps

The cheapest option is just a heap in the corner of the garden. It works, but slowly, and looks untidy. Rats and other wildlife can get to it easily. Best for large gardens where appearance does not matter.

How to Build a Compost Heap

Layering

The classic method is to add materials in layers. Start with a 10cm layer of twigs or coarse material at the bottom for drainage. Then alternate 10cm layers of green and brown material. A handful of garden soil or finished compost between layers introduces the microbes that do the work.

In practice, most people add materials as they come. The trick is to keep an eye on the balance. If the heap is wet and slimy, add brown material. If it is dry and not breaking down, add green material and water.

Size matters

A compost heap needs to be at least a metre cubed to generate enough heat to decompose quickly. Smaller heaps still work but more slowly. A small Dalek bin works because it is insulated; an open heap that small would just sit there.

Position

Site the bin on bare soil, not on paving or concrete. This lets worms and other soil life move up into the heap. Choose a sheltered spot in sun or partial shade. Avoid full shade because the heap needs some warmth to work.

Hot versus Cold Composting

Cold composting

Most home compost heaps are cold heaps. You add materials as they come, the heap slowly decomposes at ambient temperature, and you get compost in 9 to 18 months. Cold composting is easy and forgiving but slow.

Hot composting

Hot composting requires a balanced mix of green and brown, enough moisture, and regular turning. A hot heap reaches 50 to 70 Celsius and produces compost in 6 to 8 weeks. The heat kills weed seeds and plant diseases.

To hot compost, build the heap all at once with the right mix of materials. Turn it every week for the first month. The heap should be steaming in the morning. If it is not, add more green material and water.

The RHS has detailed guidance on composting for those who want to dig deeper.

Common Compost Problems

Smelly, slimy heap

Cause: too much green material, usually too much grass.

Fix: add brown material like shredded paper, cardboard or dry leaves. Mix it in with a fork. The smell should go within a week.

Dry heap that is not breaking down

Cause: too much brown material, or the heap has dried out.

Fix: add green material and water the heap until it is damp like a wrung out sponge. Cover with a piece of old carpet or cardboard to retain moisture.

Rats in the heap

Cause: cooked food or meat in the heap, or the heap is too dry (rats like dry nesting sites).

Fix: never add cooked food. If rats are present, stop adding material for a few weeks, soak the heap to make it less attractive as a nest, and consider a sealed bin like a Hotbin.

Flies around the heap

Cause: fruit waste exposed on the surface.

Fix: bury fruit waste under a layer of brown material or soil. The flies will disappear.

Slow decomposition

Cause: heap too small, too dry, or wrong mix.

Fix: make sure the heap is at least a metre cubed. Add water if dry. Add green material if there is too much brown. Turn the heap to introduce air.

Using Your Compost

As a mulch

A 5cm layer of compost around plants in spring suppresses weeds, holds moisture, and feeds the soil. This is the simplest and most effective use. See our article on preventing weeds in garden beds for how mulching fits into weed control.

As a soil improver

Dig compost into the top 20cm of soil when preparing new beds. This improves clay soil structure and adds organic matter to sandy soil. See our guide to improving clay soil.

As a potting mix

Sieved home compost can make up to a third of a potting mix. Mix 2 parts compost with 1 part loam and 1 part sharp sand for a general purpose mix. Do not use pure compost for seedlings because it can be too rich and introduce disease.

As a top dressing for lawns

Sieved compost spread thinly over a lawn in autumn improves the soil under the grass. See our article on why lawns get mossy for how soil compaction affects lawns.

Making Leaf Mould

Autumn leaves are too slow to compost with other materials. Instead, make leaf mould. Collect leaves into black bin bags, punch a few holes for drainage, tie the top, and leave for 2 years. The result is a dark crumbly material that makes an excellent mulch and soil improver.

Alternatively, build a simple leaf pen from chicken wire and posts. Fill it with leaves in autumn and forget about it for 2 years. See our autumn garden checklist for when to collect leaves.

Composting Through the Year

Spring

The heap comes back to life as the weather warms. Turn it to introduce air. Start adding grass cuttings as the lawn starts growing. Balance with cardboard or paper.

Summer

Peak composting season. The heap should be warm and active. Keep it damp in dry spells. Add weeds before they go to seed.

Autumn

Lots of material available: leaves, spent plants, grass. Separate leaves for leaf mould. This is a good time to start a new heap with the autumn clear up.

Winter

Decomposition slows right down. Keep adding kitchen scraps. Cover the heap to keep the worst of the wet off. Use the cold months to turn last year's heap.

Costs of Composting

• Plastic Dalek bin: 30 to 60 pounds
• Single wooden bay: 80 to 200 pounds
• 3 bay timber system: 200 to 500 pounds
• Hotbin: 200 to 350 pounds
• Compost tumbler: 100 to 300 pounds
• Home made from pallets: free if you can find pallets

Most councils in the UK offer subsidised compost bins through schemes like Get Composting. Check your local council website for offers before buying at retail.

Common Mistakes

Adding too much grass

Grass cuttings are 80 percent water and very high in nitrogen. A heap of pure grass turns into a smelly slimy mess. Always mix with brown material.

Not adding brown material

Most households produce far more green waste than brown. Shredded paper and cardboard are the easiest way to balance this. Keep a bin of shredded paper next to the compost bin and add a handful every time you add kitchen waste.

Letting the heap dry out

In dry summers a compost heap can dry out completely and stop working. Water it occasionally, or cover with carpet to retain moisture.

Expecting compost too quickly

Cold composting takes 9 to 18 months. Be patient. If you want fast compost, you need a hot heap with regular turning.

Final Thoughts

Composting is one of those habits that becomes second nature. Once you have a bin going and you see what comes out, you will wonder why you ever threw kitchen scraps in the bin. Good compost is the foundation of a good garden: it improves soil, feeds plants, suppresses weeds, and costs nothing but a bit of attention.

Start with a single bin and a balanced mix of green and brown. After a year you will have your first batch of compost. After three years you will wonder how you ever gardened without it.

Garden maintenance service

Frequently Asked Questions

Can I compost weeds?

Annual weeds are fine. Perennial weeds like bindweed, couch grass and ground elder should not be composted because the roots survive and regrow. Either burn them, drown them in a bucket of water for 6 weeks, or put them in the council bin.

Can I put citrus and onions in compost?

Yes, in moderation. The old advice to avoid citrus and onions was about wormeries, where they can be too acidic. In a normal compost heap they break down fine.

How do I know when compost is ready?

Finished compost is dark brown, crumbly, and smells like woodland soil. You should not be able to recognise the original materials. If you can still see whole leaves or sticks, it needs more time.

Do compost bins attract rats?

Only if you add cooked food or meat, or if the heap is very dry and provides a nesting site. A well managed heap with no cooked food is no more attractive to rats than the rest of the garden.

Further Reading

• How to improve clay soil in your garden
• How to prevent weeds in garden beds long term
• Autumn garden checklist
• Garden maintenance service

Sources and citations

This article draws on the following sources. Specific claims are cited inline where relevant.

1. CGM field records (2024-05. Site observations from gardens across Oxfordshire, Buckinghamshire, Berkshire and Bedfordshire.
2. Royal Horticultural Society (2024). RHS Gardening Advice and Plant Finder. Available at rhs.org.uk.
3. Met Office (2024). Regional climate averages, South East England. Available at metoffice.gov.uk.
4. British Geological Survey (2024). Soil parent material data for the Chilterns and Thames Valley. Available at bgs.ac.uk.