Home composting is key to sustainable and organic gardening, as well as being the ideal way to recycle waste. CAT’s gardeners have tried out all sorts of composting methods over the years. It’s been vital for creating productive growing beds on our slate tip site.

Making your own compost saves you having to buy potting media, fertilisers and soil improvers. It therefore avoids the environmental impacts of processing and transporting these products – including the climate change impact of peat extraction.

Aim to make as much of your own compost and leaf mould as possible and add this to the soil at least once a year. Once a plot is established there is no need to dig the soil over. Simply add organic matter to planting holes, or as a mulch on top.

Easy composting

What a lot of households want is a compost bin or heap that doesn’t need much attention. However, a common complaint is that unattended compost turns into a sticky, smelly porridge. This tends to happen when you’re just adding stuff like kitchen scraps, green waste and grass clippings. Piled in together, they compress into a soft mass that squeezes out the air and stops the composting process.

You need to something else – something that will keep air spaces open in the heap, while also composting down. A simple solution is to add some types of paper and card, and make ‘high-fibre’ compost. This gives you a nice mix of nitrogen-rich green waste and fibrous, carbon-rich paper/card, and should lead to good compost.

Don’t add all paper waste, because paper and card that’s in decent condition should be recycled to save resources. Stuff at the top of this list is more suitable, because recycling collections don’t usually want stained or dirty paper. When you’ve got enough for your compost, the rest can be recycled.

• Tissues and kitchen towels
• Card or paper packaging with food stains
• Crumpled or balled paper, especially if dirty
• Toilet roll tubes
• Egg boxes (when no longer good enough to refill)
• Shredded paper packing
• Corrugated cardboard
• Cereal boxes and other food products

Avoid composting what is most suitable for recycling – such as newspapers and magazines, office paper and envelopes. Paper products that are waxed or lined with foil or plastic are not good for composting, but may also be difficult to recycle in some areas.

Starting high-fibre compost

Start with crumpled card/paper at the bottom of a container, about 20cm to 30cm deep. It’s great to add worm-rich compost from a previous batch or someone else’s compost. Then add the kitchen scraps and garden waste in roughly equal amounts to the paper and card. There’s no need to be too fussy, but make sure there’s plenty of air in the heap.

The composting process will begin over the next few months. If your compost heap is in the garden, beneficial creatures should turn up and multiply. Failing that, it’s possible to buy worms from a supplier of wormery systems. As you add waste at the top the zone of decomposer activity will move up with it. In a mature heap you’ll usually find a heaving layer of worms about 15cm below the surface, doing their decomposing work.

You should find that fine, crumbly brown compost accumulates at the bottom of the heap. If you have the space, you could fill one container and then start another one while the first finishes. Otherwise, choose a container that allows for a continuous process – removing the finished compost from below as you need it. If the finished compost is a bit wet, just leave it in the open for a few days to mature.

Traditional hot composting

The classic hot composting approach works well when you have a larger garden, and a lot of waste and time. In this type of ‘thermophilic’ (heat-loving) composting, the heat generated kills off most weed seeds and pathogens. Traditionally, you would layer cardboard and green waste in such a way that it heats up very quickly. It will reach 60-70°C in a matter of days, encouraging heat-loving microscopic organisms that will compost waste very quickly.

The heat is generated by bacteria and fungi reproducing quickly and consuming the easily available materials. After a week or so they either cook themselves to death or run out of air or easily accessible food. Therefore their activity declines and the temperature starts to drop. The process is restarted by turning or mixing the heap, adding water if needed. This might happen three or four times, with usable compost ready in about six weeks.

Hot composting bins

You can buy insulated compost bins that speed up the high fibre process by maintaining a high temperature. The bins include ventilation to keeps the mix aerated. Suitable carbon-rich ingredients include paper and card, dry leaves, and finely chipped woody waste.

Petra, one of CAT’s gardeners, has been using a 400 litre Aerobin here for about a year. She says it’s been great for putting all sorts of waste in, and it’s been working as intended, without problems. There have been no problems with rodents, the bin has plenty of worms in it, and it’s composting very well. Petra also gets good ‘compost tea’ liquid from a drain at the bottom.

Bokashi

This is a system for converting kitchen scraps into a nutrient-rich material.

The Bokashi method uses a specific blend of effective micro-organisms grown on bran and molasses. These are added to the kitchen scraps in small buckets, sealed tightly, and left for a few weeks to ferment. It can then be dug in to soil, or mixed in with compost. It usually relies on bought additives, but you can read about making a bokashi-like compost activator on our blog.

Compost without a garden

A wormery is self-contained composting system, and may be appropriate if you only have a yard or balcony. They use deliberately introduced worms to deal with small but regular amounts of rich food scraps. They often have a stacking design to give a few thin horizontal layers. The worms are at the top, the compost gathers in the middle, and ‘compost tea’ collects at the bottom. The juice is good for using on houseplants, and the compost for containers and window boxes.

They do need care and attention. For example you shouldn’t add too much food, or too little, or food that’s too acidic (like citrus or onion). There are likely to be ongoing costs, such as lime to counter acidity and protect the worms.

Further Information

CAT offers group visits and workshops. See also the nature and growing books in our online shop.