Classic composting - part 2

Which raises the awkward question: what do you do with compostable material that accumulates meanwhile? Clearly, if traditional composting is to work at all, you must have at least two compost heaps. “Fill your compost bin with at least a cubic metre of waste.” Naturally, this assumes that you have a compost bin that will hold that amount. So how big are commercial compost bins?

Many retailers sell their own version of the classic, wooden “New Zealand” box; a quick check of catalogues and websites shows that the standard box bin varies from 0.3–0.75 cubic metre (11–26 cu.ft).

You can find larger bins, up to 1.3 cubic metres (46 cu.ft), but you have to look quite hard to find them.

Plastic compost bins, of the type often provided free or at a subsidized price by local government, are generally smaller. A leaflet from my local authority lists three bins, ranging from 0.23–0.6 cubic metres (8–21 cu.ft). Fancier options, such as bins disguised as beehives and tumblers, are smaller still. I’m forced to conclude that manufacturers of compost bins do not expect the average gardener to assemble a cubic metre of compost at one go.

In fact, although this is unlikely to happen to you, spontaneous fires at commercial composting sites are not that uncommon, and are usually caused by a large heap that is (at least

in part) too dry. The message is that moisture content is critical: it must be high enough to allow composting to occur, but not so high that heat is lost too quickly. On a domestic scale, the moisture content of a compost heap is difficult to measure or control: quite small variations in moisture content are probably responsible for the rather unpredictable behaviour of the typical heap. Finally, does it work? That is, if you have survived the assault course needed to assemble a compost heap in the required manner, will it do what it should do? The Royal Horticultural Society research described previously plainly shows that it probably won’t. The only simple way of ensuring a compost heap gets hot and stays hot is to make it larger than recommended by

the books, and certainly larger than a typical compost bin.

It seems clear that classical hot composting was designed by (and for) people with big gardens, plenty of space, and ready access to outside sources of compost materials, typically animal

manures. In such gardens, classical composting is still alive and well. At the RHS Garden, Wisley, in the UK, huge quantities of waste are chipped, shredded, and mixed by special machinery, then

blended into huge heaps, typically 2x4x12m (6x12x40ft) in size, or about 100 times the minimum recommended size of the domestic heap. This makes excellent compost in about four months, but it’s a process the ordinary gardener can only dream about.

Of course, I’m not saying it’s impossible to make a traditional, hot compost heap in an average bin. It’s just that you will have to take some elaborate precautions, probably including more than one of these steps:

• importing composting material from outside the garden

• trying to make compost only in summer

• installing effective insulation around your bin

• siting the compost bin in the sunniest, most sheltered spot

• moving to somewhere with warmer summers.

At which point, the average gardener could be forgiven for

concluding that the game is hardly worth the candle. Gardening

is supposed to be fun, after all.

Classic composting

The traditional advice for constructing a classic compost heap is quite simple. First, collect together a mixture of soft, nitrogenrich waste and tougher, carbon-rich material. Shred any tree and shrub prunings.

Second, start filling your compost bin with layers of different materials, adding a spadeful of compost or soil now and then – the right micro-organisms will colonize your heap eventually anyway, but there’s no harm in giving them a helping hand. Carry on until your heap measures at least one cubic metre (1 cu.yd), or more if possible. If the heap seems dry, water it. Cover it with the bin lid or a piece of old carpet.

Your heap should soon start to get hot. When it starts to cool, turn it and it will heat up again. When it starts to cool again, turn it for a third time, and leave until done. Sounds simple, doesn’t it? Unfortunately, it’s this stately home approach that caused generations of gardeners to abandon the whole idea of making compost. In fact, this

apparently simple advice is

riddled with weasel words

that gloss over real difficulties.

“Turn your heap when it starts to cool down.”

Modern gardeners are busy people, with their compost heap somewhere near the bottom of their list of priorities. Turning a large compost heap is hard work, and doing it twice sounds like adding insult to injury. There’s also the anxiety of whether you’ve got the timing right. Is it cooling down yet? Have I left it too long?

“Collect together at least a cubic metre of waste.”

Pardon?

How often does the owner of a modern, small garden have a cubic metre (cu. yd) of waste at one time? Pause at this point and try to visualize a cubic metre of garden waste (go and get a tape measure if necessary).

“Well then,” goes the advice, “gather the materials over a

period of time.”

OK, but where do you store this stuff while you are waiting to collect enough? An even more interesting question is how you stop the green waste from starting to compost before it goes on the compost heap. Keep it in the fridge maybe?

Something else the books never mention. As described, composting is clearly a batch process, like putting a load in the washing machine. A full load of compost material is assembled and, after a time, finished compost results.