Many beginners ask this question when they start out composting.
The terms Browns and Greens can be a useful description for the carbon-rich and nitrogen-rich organic materials that are needed to provide composting creatures with a good diet.
These insects and micro-organisms have basic requirements for food just like the rest of us. If the balance is wrong they won’t be as happy and won’t decompose the organic material as effectively. But don’t let this put you off. Anyone who composts is constantly figuring out how much carbon to add to the bin. It becomes an interesting hobby and – dare we say it – fun.
Nobody is going to come round giving your finished compost marks out of 10 (unless that’s the way you roll) and it’s unlikely you’ll get a mob of angry worms waving placards at your door. (If you do, be sure to upload the footage on YouTube.)
The micro-organisms need protein (which is rich in nitrogen) for growth, and sugar (rich in carbon) for energy, much of which is released as heat.
Dead leaves and woody waste, such as twigs and branches, are rich in carbon, and green grass and green leaves are rich in nitrogen. So, we think of carbon as Browns and nitrogen as Greens.
When it comes to garden waste, it’s easy to remember that dead leaves and branches are Browns while fresh leaves and grass are Greens. But confusion can arise when it comes to waste that’s not from the garden. Not every brown item is carbon-rich and not all Greens are green in colour. For example, coffee grounds and manure might be brown but they’re not composting Browns; they’re rich in nitrogen, so are classified in composting terms as Greens.
Nancy Birtwhistle says in her book The Green Gardening Handbook that she finds the traditional Browns and Greens compost terminology confusing, preferring to think in terms of Wet and Dry contents.
Michael Kennard, of the food-waste composting organisation Compost Club, makes the same point in his booklet How to Hot Compost – The Basics. He encourages beginners to think in terms of nitrogen and carbon content (C:N ratio).
The ideal C:N ratio is considered to be 30:1 but it would be difficult to calculate this exactly as every item has a different ratio. Most plant materials are a mixture of both, but more carbon than nitrogen as they get older and tougher.
A good guide is to simply add equal amounts of carbon to nitrogen, then observe and make adjustments if your compost lets you know something is wrong. For example, if it starts to smell, there’s too much nitrogen (and poor aeration). If breakdown is very slow, there’s too much carbon.
Here’s a quick guide to common organic materials for composting:
GREENS: NITROGEN
- Food waste
- Fresh grass clippings
- Fresh annual weeds
- Flowers
- Plant debris
- Seaweed/kelp
- Coffee grounds/filters
- Tealeaves, tea bags (non-plastic)
- Natural fabrics (cotton, wool)
- Herbivore manure
BROWNS: CARBON
- Dead leaves
- Shrub prunings – twigs, branches, stalks
- Cardboard – tape and stickers removed
- Pine needles/ cones
- Corn cobs (may have to go through the composting process several times)
- Brown paper bags, scrunched up
- Sawdust from untreated wood
- Straw
- Cardboard egg boxes
- Wood chips
- Newspaper and junk mail
Keeping carbon
A little planning goes a long way when it comes to having enough carbon content to hand. Gardens usually provide plenty of nitrogen in summer and carbon in autumn. Many people bag up and store dead leaves in autumn so that they’re readily available throughout the year. Store these leaves and other carbon-rich content near your compost bin in lidded containers or tied bags so they don’t get wet and start to break down. Then when you add food waste or grass cuttings to the bin, you can add your carbon at the same time.
Grass mowings are a good compost activator but if a large amount is added at one time the compost can become too wet and the grass can clump together. So, add grass in thin layers, alternating with layers of dead leaves or paper.
Remember that chopping or shredding Browns increases the surface area in contact with microbes in the pile, which makes for faster breakdown. Smaller pieces also make turning the pile easier.
A chipper/shredder can save time and effort or use a pair of hedge clippers to chop materials on a board.
