The Centre for Alternative Technology (CAT) in Wales is championing a variation on ‘cold’ composting they are calling the ‘High Fibre’ method that utilises paper and cardboard as well as the normal greens and browns.

Peter Harper at CAT explains it this way:

“One undoubted success [at CAT] has been the use of nonrecyclable paper and cardboard as a bulking agent for putrescibles and soft garden wastes [in home composting]. For many households, kitchen wastes and grass clippings are the main organic arisings and these are ones that traditionally have given the most trouble to home composters, because they lack structure, are often too moist, and contain too little carbon [i.e., ‘browns’].

“The addition of cellulose in the form of balled or ‘scrunched’ cereal boxes, used tissues and kitchen towels, toilet-roll spindles, soiled newspapers etc, corrects all these deficiencies at a stroke. As it happens these materials are readily available in any household in more or less the right quantities, at the right scale, and the right timing to combine almost perfectly with the other organic arisings. Everything goes onto the heap ‘as it comes’. It does of course require another source-separation category unfamiliar to most householders, but is easily learned and incorporated into kitchen routines.

“This simple mixed system has been tested for five years in the trial household [at CAT in Wales], using large open containers with a floor area about 1m², on a yearly cycle, taking all kitchen waste including cooked material, plus household fines ..., soft garden wastes, weeds and spent composts.

“It differs from standard composting practice in that there is no attempt to establish a thermophilic [i.e., HOT] phase. There is some heating, but it does not seem important. Instead the entire mass is dominated by visible invertebrate decomposers, principally brandling worms but also woodlice, slugs, insect larvae, springtails and mites, plus carnivores such as centipedes and staphylinid beetles.

“There is no need for turning. A rich, dark layer of invertebrate frass builds steadily from the bottom, and in the summer is only a few inches below the surface under the fresh material. The process is slower in the winter but still vigorous. There are occasionally anaerobic pockets but they do not last long. Smells are minimal. There are fruit flies but in relatively small numbers, and they can be eliminated if necessary by a layer of fresh grass clippings. There have been no vermin problems!

“...This continuous system matches the typical pattern of household production of kitchen and non-recyclable cellulose wastes. Compost can be removed at any time from the bottom provided there is access, or the process can alternate between two containers, leaving one side to finish and act as store until the compost is required. The compost itself is fine enough for direct use. It usually does not require riddling, although pieces of plastic might need removing.

“...What are the snags? The most obvious one is that it does not deal with woody waste, which has different properties and a different breakdown cycle. Shredded woody waste could be used, and would be a useful bulking agent, but there would still be twiggy bits in the compost after one year.

“...Over the years we have refined the list of paper products that work best and which – such as drinks cartons – should not be used at all.

“Grass is slightly problematic. Grass clippings have similar characteristics to kitchen waste and in small quantities can be incorporated into the system without further ado. In fact they seem to be a positive asset. ...As all gardeners know, a large mass of grass clippings can turn to smelly slime in a remarkably short time. All this is especially true if the garden has big lawns.

“Several simple ways round this have been tried, the main one being a nearby store of ‘extra’ cardboard in the form of corrugated cartons. The cartons are crudely ripped and buckled to create complex surfaces and mixed with the grass to give cells of about 1-5 litres. This process can be mixed with the rest of the compost system, or carried out separately, which can give a very clean, usable compost in a under six weeks. ...

“The finished HFC compost is very pleasant to handle and can be used straight away as a potting medium without combining it with other media. In trials so far it has produced magnificent plants. It has succeeded both as seed and potting compost....”