The Gardener's LogComposting at Home: A Simple Guide That Actually Works
Compost is the best thing you can add to garden soil, and you can make it from things you would otherwise throw away. Autumn is a good time to start, because there is plenty of material around: fallen leaves, spent plants, the last lawn clippings and kitchen waste. Home composting has a reputation for being complicated, but the basics are straightforward.
How composting works
Composting is the process of microbes, fungi, worms and other creatures breaking down organic material. They need four things: food (your waste), air, moisture and warmth. Get the balance of those roughly right, and nature does the rest.
Choosing a bin
You can compost in an open heap, but most gardens use a bin to keep things tidy, retain warmth and moisture and deter pests.
- Plastic "dalek" bins are cheap, widely available and good at holding moisture. They are fine for most gardens.
- Wooden bins or pallet bays allow more airflow and take bigger quantities, and a three-bay system lets you turn material from one to the next.
- Wire mesh bins are best for leaves (see clearing leaves).
Put the bin on bare soil, not paving, so worms and other organisms can move in. Choose a spot that is level, reasonably sheltered and accessible. If you can have a bit of sun it helps, but the shade is fine too.
Greens and browns
The key to good compost is a mix of two types of material.
Greens are nitrogen-rich and usually wet: vegetable and fruit peelings, tea bags (check that they are plastic-free), coffee grounds, fresh grass clippings, young weeds and plant trimmings.
Browns are carbon-rich and drier: fallen leaves, shredded cardboard and paper, torn-up egg boxes, straw, woody prunings (chopped small), and sawdust in small amounts.
A good rule of thumb is roughly equal volumes of greens and browns, though the exact ratio is less important than avoiding too much of one type. Too many greens give a wet, smelly slime. Too many browns slow everything down and the heap stays dry and inactive. If you only have grass clippings, mix them with shredded paper, or leaves, in layers of a few centimetres at a time.
What to avoid
- Cooked food, meat, fish and dairy: they attract rats and flies.
- Dog and cat faeces: health risks.
- Diseased plants: blight-affected potatoes and tomatoes, and club-root brassicas, can survive in a cool heap and spread disease.
- Perennial weed roots such as bindweed and ground elder, and weeds with seeds, unless you are sure your heap gets hot or you have dried them thoroughly first.
- Glossy magazines, coal ash, barbecue charcoal and anything plastic or synthetic.
- Treated wood or sawdust from treated timber.
Cooked food waste can be dealt with in a closed "Bokashi" bin or in the council food waste collection if you have one.
Get the moisture and air right
The ideal heap is as damp as a wrung-out sponge. If you squeeze a handful, a drop or two of water should come out. If it is too dry, add water or green material. If it is too wet and smelly, add more browns, such as shredded cardboard, and turn the heap.
Air matters, because without it the heap turns anaerobic and smelly. Chop up bulky material, mix coarse, woody stuff in with soft material, and turn or mix the heap from time to time. Many gardeners turn it every few weeks in the warm months, and less in winter. A garden fork or a compost aerator tool works fine.
Hot or cold?
Hot composting needs a large volume, at least about a cubic metre, plus a good mix and regular turning, and can produce usable compost in a few months. It reaches temperatures high enough to kill many weed seeds and some pathogens.
Cold composting is the easy, relaxed version. Add material as it becomes available, do not worry too much, and wait. It generally takes six to twelve months or more, and the compost may contain some weed seeds, but it works and takes little effort. Most home gardeners end up cold composting, and that is fine.
Winter composting
Composting slows down in cold weather but does not stop. Keep adding material, cover the heap with a lid, a piece of carpet or a tarpaulin to retain warmth and prevent it getting waterlogged, and chop up bigger items. Expect that the compost will be ready next summer or autumn.
How to tell when compost is ready
Finished compost is dark brown, crumbly and smells earthy, like a woodland floor. You should not be able to recognise most of what went in, although woody bits and eggshell may remain. Sieve it if you like and put the lumps back in the heap. The bottom of the bin is usually ready first, so remove the bin or open the hatch, and shovel from the bottom.
Using compost
- Mulch over borders, 5 to 7 cm thick, as a weed-suppressing layer. See controlling weeds in autumn.
- Soil improver dug into vegetable plots.
- Potting mix: home compost is usually too rich and variable for seedlings, but it can be mixed with sharp sand, grit or loam for larger pots.
- Lawn top dressing: sieved compost mixed with sand can be brushed in, in thin amounts.
Peat-free
If you buy compost, choose peat-free. Peat extraction damages valuable wetland habitats and releases carbon, and good peat-free options are now available. Your own compost helps reduce the need to buy any.
Common problems
| Problem | Likely cause | Fix |
|---|---|---|
| Smelly, slimy | Too many greens or too wet | Add shredded cardboard, turn it |
| Dry, nothing is happening | Too many browns or too dry | Add water and greens, mix |
| Flies | Exposed food waste | Bury kitchen waste in the heap and cover it |
| Rats | Cooked food or open bottom | Avoid cooked food, use a lid and fine mesh |
| Ants | Too dry | Moisten it |
A simple routine
- Keep a small caddy in the kitchen for peelings.
- Add them to the bin with a similar amount of brown material.
- Mix in grass clippings in thin layers.
- Check moisture occasionally and turn when you have time.
- Be patient.
If you are tidying up after trimming a hedge, or pruning, shred woody pieces before adding them. See hedge trimming for tips on disposal.