At a glance
- Compost is the best fertiliser you can get for free: garden and kitchen waste turn into dark, crumbly soil that feeds your soil life.
- The whole secret lies in one ratio: you mix green, nitrogen-rich material with brown, carbon-rich material. Too much green stinks, too much brown does not rot.
- Compost needs air and moisture. Damp like a wrung-out sponge and loosely layered, and the microbes work best.
- Not everything belongs in it. Cooked food, meat, diseased plants and seeding weeds have no place on the compost.
A good compost heap is the heart of a healthy garden. It turns what many throw in the bin into valuable humus soil and closes the cycle in the bed. And best of all: it costs nothing but a little attention.
Many shy away from compost because they fear a rotting, smelly corner. But that only happens when the balance tips. Understand the one decisive ratio behind it and you can always make a compost that smells of forest floor instead of rot.
What happens in the compost
In the compost, billions of bacteria, fungi, worms and tiny creatures are at work. They break down the organic material and rebuild it into humus, that dark, crumbly substance that makes soil fertile. Heat is produced along the way; a well-running heap can really warm up.
For these helpers to work, they need the right food and good conditions. That is exactly what composting is about: you put together a balanced menu for the microbes and provide air and moisture. They do the rest by themselves.
Green and brown: the decisive ratio
Everything compostable belongs to one of two groups. The art lies in mixing both, instead of piling up just one.
The four adjusting screws
- Green material (nitrogen)
Damp and nutrient-rich: kitchen scraps, grass clippings, fresh greenery, coffee grounds. It gives the microbes protein but compacts and rots quickly if it lies alone.
- Brown material (carbon)
Dry and loose: autumn leaves, straw, shreddings, chopped cardboard, thin twigs. It brings structure and air and is the energy source for the decomposition.
- Moisture
The heap should be damp like a wrung-out sponge. Too dry and the rotting stalls, too wet and it goes rotten. Water as needed or mix in brown material.
- Air
The good microbes need oxygen. Layer loosely, mix in coarse brown material and turn the heap now and then. Then it stays airy and smells pleasant.
How to set up the compost
Choose the right spot
Place the compost in part shade and with direct soil contact, so worms and soil creatures can move in. An open wooden composter or a thermal composter both work.
Start with a coarse layer
Right at the bottom goes an airy layer of twigs or shreddings. It provides ventilation from below and prevents waterlogging.
Mix green and brown
Add green and brown material in turn, always nicely mixed. As a rule of thumb, roughly equal parts, when in doubt a little more brown. Chop up coarse material and it goes faster.
Keep it damp and turn it
Check the moisture and water in dry spells. Turning the heap every few months brings in fresh air and speeds the rotting noticeably.
Recognise ripeness and harvest
After about six to twelve months the compost is ready: dark, crumbly and with the scent of forest floor. Sieve out the coarse bits and return them to the next heap.
This does not belong on the compost
Some things have no place on the garden compost. Cooked food, meat, fish and cheese attract rats. Diseased plants such as haulm affected by late blight or clubroot roots spread the pathogen further. Seeding weeds and root weeds like ground elder and couch grass germinate or sprout again. And cat or dog faeces, glossy paper and coal ash stay out too.
How to speed up the rotting
If you want finished compost faster, chop up the material, mind a good green-brown mix and turn the heap regularly. Every turn brings in oxygen and heats up the rotting. A handful of finished compost or good garden soil as a starter brings the right microbes along at once.
Green and brown in balance, damp like a wrung-out sponge and always nicely airy. Then the compost smells of forest, not of rot.
The core rule of composting
Frequently asked questions
Why does my compost stink?
Almost always because too much damp green material sticks together without air and goes rotten. Mix in plenty of brown, loose material such as leaves or shreddings, and turn the heap. Then oxygen gets in and the smell disappears.
How long does it take for compost to be ready?
Usually six to twelve months. With fine chopping, a good mix and regular turning it goes faster; an untouched heap takes longer. It is ready when it is dark and crumbly and smells of forest floor.
May I compost citrus peel and onions?
In small amounts yes. Large amounts of citrus peel rot slowly and acidify, and many compost worms dislike lots of onion. In moderation and well distributed, both are no problem.
Do I need a shop-bought compost accelerator?
No. A good mix, moisture, air and some finished compost as a starter are quite enough. You bring the necessary microorganisms along yourself, so expensive products are superfluous.
Can I compost on a balcony without a garden?
Yes, with a worm bin. In it, compost worms turn kitchen scraps odourlessly into valuable worm humus. That works in a small space and even indoors.
Sources
- German Federal Environment Agency: composting in the garden
- Bavarian State Institute for Viticulture and Horticulture (LWG): composting properly
- Related in the magazine: Feeding the soil organically and Planning crop rotation
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